A study of more than 19,000 teens and adults across the UK provides some of the first compelling, peer-reviewed, and large-scale evidence that you need both doses of two-dose vaccines to get good protection from the Delta variant.
The findings from Public Health England suggest that vaccine protection against Delta is very strong when people get both shots.
When patients were fully vaccinated, with two shots both given at least two weeks to take effect, Pfizer’s COVID-19 vaccine became about 88% effective against symptomatic COVID-19 from the Delta variant, while AstraZeneca’s vaccine was 67% effective against it.
In their comparison of a patient’s vaccination status, their COVID-19 test results, and variant sequencing to determine whether their infection was caused by the Alpha (B.1.1.7) variant or Delta, researchers were able to determine how well the Delta variant evaded vaccine protection.
With only one shot on board, Pfizer’s vaccine was just 36% effective against symptomatic Delta cases, while AstraZeneca’s vaccine was 30% effective, the researchers found.
Getting two shots of a vaccine gives the body a chance to develop a more robust immune response to COVID-19, which ramps up its attack on the virus.
“That’s the reason why the second dose is much more reactive,” professor Akiko Iwasaki, who studies viruses at Yale, previously told Insider. “This is a sign that your immune system is working because you develop a much worse response the second time, based on these antibodies and T cells that are detecting the viral antigen and attacking your own cells.”
Even with Delta prevalent, all the usual pandemic protocols, including masking, distancing, and limiting exposure, still help.
“Even modest mask use combined with vaccination can really put the brakes on even the Delta variant,” Christopher Murray, the director of the Institute for Health Metrics and Evaluation, previously told Insider.
The data for how well COVID-19 vaccines work against the Delta variant isn’t clear cut.
The World Health Organization said Tuesday, July 6, that COVID-19 vaccines from Pfizer-BioNTech and AstraZeneca worked well against severe COVID-19 caused by Delta, in comparison to other variants. But the vaccines may offer less protection against symptomatic illness – rather than severe disease – caused by Delta compared to other variants, it said.
Here’s how much protection COVID-19 vaccines give you against symptomatic Delta infections, based on the best available data from four studies.
A UK-based study from May found that two doses of either AstraZeneca or Pfizer’s vaccine were highly effective against the Delta variant, from two weeks after the second dose.
33% effective after one dose, 88% effective after two.
33% effective after one dose, 60% effective after two.
Canadian study: Pfizer 87% effective after two doses, Moderna 72% after one dose
A Canadian study posted on Saturday, July 3, found that two doses of a COVID-19 vaccine worked as well against Delta as they did against the Alpha variant, which was previously dominant in the US.
The study hasn’t been scrutinized by experts in a peer-review.
56% effective from 14 days after first dose, 87% effective after two doses.
67% effective from 14 days after first dose. Not enough data for two doses.
72% effective from 14 days after first dose. Not enough data for two doses.
Israel study: Pfizer 64% effective after two doses
The Israel Ministry of Health said on Monday, July 6, that Pfizer’s vaccine worked slightly less well against the Delta variant than previous estimates. The number of people who got infected during the study period was small, and the figure may have included asymptomatic infections.
64% effective after two doses.
Scotland study: Pfizer 79% effective after two doses, 60% for AstraZeneca.
A Scotland-based study published as a letter to the Lancet medical journal on June 14 found that Pfizer’s vaccine offered “very good” protection against the Delta variant.
79% effective after two doses, at least 14 days after the second dose.
60% effective after two doses, at least 14 days after the second dose.
Why the numbers vary
Percentage efficacy for vaccines is the proportion of people that get full protection after a vaccine. With 80% efficacy, 80% of people have full protection, and 20% don’t.
It becomes harder to measure how well vaccines work in the real world compared with trials, because you can’t control who gets vaccinated and who doesn’t. Other differences between the two groups could influence the risk of getting sick from COVID-19. For example, those who chose not to get vaccinated could also be more likely to put themselves in risky situations that may expose them to the virus.
The numbers can also vary because they depend on numerous factors, including what you’re measuring, when you measure it, the age of the population you’re measuring it in, and whether there’s been previous COVID-19 infections.
Stephen Evans, professor of medical statistics at the London School of Hygiene & Tropical Medicine, told Insider that in general, the more severe the illness caused by Delta, the better the COVID-19 vaccines appeared to work against it. But the evidence on vaccines’ effectiveness wasn’t strong, he said.
The evidence in favor of a mix-and-match approach to coronavirus shots is growing.
Early data from a UK study, though not yet been peer reviewed, indicates that mixing the Pfizer and AstraZeneca vaccines yields a greater immune response than two doses of AstraZeneca’s shot. The researchers measured antibody levels among 830 volunteers who received either two doses of the same vaccine or a combination of Pfizer and AstraZeneca, four weeks apart.
Volunteers who got AstraZeneca’s shot followed by Pfizer’s showed nearly the same antibody levels – and an even higher number of T-cells – as those who’d received two doses of Pfizer. By contrast, volunteers who got Pfizer’s shot first and AstraZeneca’s second had slightly lower antibody levels than the reverse combination. But those levels were still were roughly five times higher than the antibody response after two doses of AstraZeneca.
“Mixing these two vaccines not only appears to be safe, but can give a higher immune response than the standard dosing regimens,” Deborah Dunn-Walters, a professor of immunology at the University of Surrey, said in a statement.
There are some caveats, though: The UK study examined immune-system responses, not real-world infection rates. Plus, research has shown that AstraZeneca’s vaccine is more effective when the doses are given 12 weeks apart. So the UK team is running a separate trial based on that interval, and those results haven’t been released yet.
For now, though, some experts think it might be beneficial to recommend a booster shot of Pfizer’s or Moderna’s mRNA vaccine for people who received a different initial shot.
“From this study, people who have had a first course of AstraZeneca should probably be offered the Pfizer vaccine (or possibly Moderna or Novavax dependent on the future trial data from this study) in the autumn rather than a repeat AstraZeneca,” Paul Hunter, a medicine professor at the University of East Anglia, said in a statement.
“People who had a Pfizer first course may not need an autumn booster,” he added, “but if they do, then it probably does not matter much which vaccine they are offered.”
Some countries already let residents mix and match
Even before coronavirus vaccines came out, some research had already indicated that mixing and matching vaccines in general could yield better results. Johnson & Johnson’s Ebola vaccine, for instance, uses an adenovirus shot followed by a modified version of a poxvirus. Researchers have tested different vaccine combos for a future HIV shot, too.
Already, some countries have started allowing residents to mix and match coronavirus vaccines.
Canada announced earlier this month that the Pfizer and Moderna shots could be used interchangeably, given the country’s low vaccine supply. Meanwhile, several European countries – including Germany, Sweden, France, Spain, and Italy – have said that people who received an initial dose of AstraZeneca’s shot can choose a different vaccine for their second dose, given the reports of rare blood clots linked to AstraZeneca’s vaccine.
Yet another mix-and-match study, this one funded by the National Institutes of Health, is giving participants a booster of Moderna’s vaccine after their initial regimen of Moderna, Pfizer, or Johnson & Johnson.
Joseph Hyser, a participant in that trial, recently told Insider that his side effects were a bit more severe after a booster of Moderna’s vaccine than after each of his doses of Pfizer’s vaccine. He said he woke up the day after his booster feeling “like I had done a very rigorous gym workout,” with chills and arm soreness – like he’d gotten a “hard punch in the shoulder.”
The NIH study could offer much-awaited insight into whether following J&J’s single-dose shot with a Moderna booster offers similar protection to a two-dose mRNA vaccine. But some experts who got J&J’s shot aren’t waiting. Angela Rasmussen, a virologist at the University of Saskatchewan, tweeted on Tuesday that she got the Pfizer vaccine to “top off” the J&J vaccine she received in April.
Rasmussen encouraged people who’d had J&J’s shot to speak with healthcare providers about getting an extra dose.
“We shouldn’t wait to make recommendations about this,” she wrote.
Hilary Brueck and Dr. Catherine Schuster-Bruce contributed reporting.
The UK is delaying the second dose of the vaccines for up to 12 weeks for most people to prioritize giving people their first shot because of an initial shortage of vaccines. In the US, the Centers for Disease Control and Prevention has recommended giving second doses of Pfizer’s vaccine 21 days after the first, and 28 days after the first for Moderna, with an interval of up to six weeks in “unavoidable” situations.
The data for how well the vaccines work after one dose isn’t clear cut – it depends on what you’re measuring, and when you’re measuring it. Stephen Evans, a professor of medical statistics at the London School of Hygiene & Tropical Medicine and a former drug-safety committee member at the European Medicines Agency, helped Insider break down the data.
Evans said the Food and Drug Administration presentation of the data from late-stage trials of each vaccine was generally the best data available. This is how much protection one shot of each vaccine gives you, based on that data.
Pfizer-BioNTech: at least 80%
Pfizer’s shot was 52.4% effective at protecting against COVID-19 with symptoms between the first and second dose, according to the FDA documents. But the 52.4% figure includes the 11 days before protection kicks in after the first dose, so the real percentage could well be higher.
The true value lies between 29.5% and 84.5%, according to the FDA documents. There was a wide range because not many people caught COVID-19 in the trial during this time period.
Pfizer’s shot was 100% effective at protecting against hospitalization and death. This was based on a small number though – only four people got severe COVID-19 in the trial after receiving placebo rather than the vaccine.
Evans said there was “pretty clear evidence” that you get at least 80% protection – and “probably” better than 90% – for Pfizer’s vaccine against COVID-19 with symptoms after a single dose. He said you couldn’t be absolutely sure what happens after 21 days because it hadn’t been fully tested.
Evans said this was based on his overall reading of the trial data used by the FDA in their briefing document before authorization.
Moderna: at least 80%
Moderna’s vaccine was 69.5% effective at preventing COVID-19 with symptoms between the first and second dose, with a true value between 43.5% and 84.5%. There was a fairly wide range because the number of people that caught COVID-19 in the trial during this time period was low.
The 69.5% figure includes the 13 days before protection starts, so the real percentage could be higher.
There were a small number of people in Moderna’s trial – about 7% – that didn’t get their second dose for unknown reasons. In this group, the shot was 50.8% effective at preventing COVID-19 with symptoms for up to 14 days after the first dose and 92.1% effective after 14 days.
It is unclear how well one shot of the vaccine protects against hospitalization and death because not many people got severe COVID-19 – two in the vaccine group and four in placebo.
Evans said that you get at least 80% protection – and probably better than 90% – for Moderna’s vaccine against COVID-19 with symptoms after a single dose for 28 days. After 28 days it was unclear because it hadn’t been tested. Again, this was based on his overall reading of the FDA data, he said.
AstraZeneca: more than 70%
Evans said it was harder to ascertain a figure for AstraZeneca’s vaccine because late-stage trials used differing study designs, and a large US study was ongoing. The FDA also has not yet presented the data for the shot in the same way it has done for other vaccines.
A single dose of AstraZeneca’s shot was 76% effective at protecting against COVID-19 with symptoms for at least 90 days, according to late-stage-trial data published in The Lancet on February 19. The study authors also reported that one dose provided 100% protection against hospitalization, but the numbers were small.
Based on his reading of existing studies, Evans said the single-dose efficacy for AstraZeneca’s vaccine was probably at least 70% against COVID-19 with symptoms for the first 90 days. After this time period, it’s unclear, he said.
Johnson & Johnson: 66%
J&J looked at protection against moderate to severe COVID-19 in trials, rather than symptomatic COVID-19, like Pfizer, Moderna, and AstraZeneca.
Protection kicked in at 14 days and was 66.1% effective at 28 days. The vaccine’s efficacy varied depending on the country it was used in – it was 72% effective in the US but 64% and 68% effective in South Africa and Brazil, respectively. These countries both have coronavirus variants circulating that could partially evade antibodies.
What percentage efficacy means
Percentage efficacy for vaccines refers to the proportion of people that get full protection after a vaccine. With 80% efficacy, 80% of people have full protection, and 20% don’t.
For those who get full protection the first time around, the second shot improves the quality of the immune response and its durability.
For the people who don’t get full protection with the first shot, some will get full protection after the second dose. Some people won’t ever get full protection from a vaccine because their immune system doesn’t respond at all.
The latest real-world data: One shot significantly reduces infections and transmission
A UK study found Pfizer or AstraZeneca’s vaccine cut COVID-19 infections with symptoms by 72% after one dose, and protection probably held up for 10 weeks. Protection from Pfizer’s vaccine rose to 90% after two doses. The study hasn’t been peer-reviewed.
A US study of essential workers found that a single dose of Pfizer of Moderna’s COVID-19 vaccines were 80% effective against all coronavirus infections from 14 days.
A Scottish study found that a single dose of Pfizer’s vaccine was 91% effective against hospitalization at 28 to 34 days following vaccination. One dose of AstraZeneca’s vaccine was 88% effective against hospital admissions after the same time period.
A UK study found that a single dose of either Pfizer or AstraZeneca’s vaccine cut spread of symptomatic COVID-19 within a household by up to 50%.
A South Korean study found one dose of Pfizer’s vaccine was 89.7% effective at preventing COVID-19 in South Koreans aged over 60, at least two weeks after vaccination. AstraZeneca’s vaccine was 86% effective at preventing COVID-19 after one dose. The severity of illness that the shots protected against was unclear – generally they’re more effective at preventing COVID-19 infections that caused hospitalization or death.
An English study found that a single dose of either Pfizer or AstraZeneca’s vaccine was about 80% effective at preventing hospitalization in people over 70-years-old. Protection lasted for at least 6 weeks, including against the Alpha variant first identified in the UK.
An Israel study showed that Pfizer’s vaccine was 54% effective against symptomatic COVID-19, from 13 days to 24 days after vaccination, a figure comparable to the late stage trial data presented to the FDA.
A UK study estimated that a single dose of either Pfizer or AstraZeneca’s vaccine was between 56% and 62% effective at preventing COVID-19 infection caused by the Alpha variant in people over 75 years-old, four to seven weeks after the first dose. The severity of illness that the shots protected against was unclear, but probably included asymptomatic infections.
A UK study estimated that one dose of Pfizer vaccine was 79.3% effective at reducing the risk of hospitalization from COVID-19 in people aged over 80. A single shot of AstraZeneca’s was 80.4% effective, the researchers said.
Newest data suggests second shot provides better protection against variants
Real-word data from the UK posted May 23 by Public Health England showed that Pfizer’s and AstraZeneca’s COVID-19 vaccines worked better against the variants when two doses were given rather than just one. Both vaccines were 30% effective against COVID-19 with symptoms caused by the Delta variant, first identified in India, three weeks after the first dose.
This was boosted to between 60% and 88% effectiveness two weeks after the second dose. The two vaccines were 50% effective against COVID-19 with symptoms against the variant first found in the UK, Alpha, three weeks after the first dose. This increased to between 66% and 93% two weeks after the second dose.
Dr. Anthony Fauci, President Joe Biden’s chief medical advisor, said on June 8 that getting two doses of COVID-19 vaccines would stop the Delta variant from spreading across the US. In the UK, Professor Deborah Dunn-Walters, chair of the British Society for Immunology COVID-19 Taskforce, said in a statement on June 4 that two doses of Pfizer’s vaccine were “critical for protection” against emerging strains of the virus.
German scientists say they’ve figured out why some COVID-19 vaccines cause unusual blood clots in rare cases.
The team of scientists from Goethe University in Frankfurt, Germany, said Wednesday that the delivery mechanism for AstraZeneca and Johnson & Johnson’s vaccines was responsible for causing blood clots after immunization.
All existing COVID-19 vaccines work by delivering a piece of genetic code into the body. This teaches the body to create a harmless part of the virus, which triggers an immune response. The body can then stage the same response if it later detects the real virus.
Vaccines that use mRNA technology, including Pfizer’s and Moderna’s, deliver the genetic material to the fluid part of the cell. Adenovirus-based vaccines, such as J&J’s and AstraZeneca’s, deliver it to the central part of the cell, called the nucleus, the scientists said in a study, which hasn’t been scrutinized by other experts in a peer-review.
According to the scientists, this is where the issue lies. While the harmless part of the virus is being made in the nucleus, bits of genetic material can break off, creating “mutant” proteins that leave the cell and travel around the body. Blood vessel walls respond to these proteins, which triggers blood clots, they said.
Unusual blood clots, particularly in the brain, are a rare side-effect of both vaccines, according to regulators. For AstraZeneca’s vaccine, 86 cases of unusual blood clots were reported out of 25 million people that had received the shot as of March 22, according to the European Medicines Agency (EMA). For J&J’s vaccine, there were eight reports of serious blood clots as of April 13, when more than 7 million people had received the shot, according to the EMA.
Young women have had the clots more often than other groups. The scientists suggested that older people are less likely to get the clots partly because their immune responses is weaker. They added that women naturally have stronger immune responses than men.
The German scientist’s theory hasn’t been proven. Researchers from Bristol University said in October that the protein made by the vaccine inside human cells accurately reflected the genetic instructions.
Other theories also exist. One is that the blood cells in the body that cause clotting, called platelets, are “activated” post-vaccination and cause clots.
Jonathan Ball, professor of Molecular Virology at University of Nottingham, told Insider in a statement Thursday that the new research posed a “really interesting hypothesis.”
The data highlights that production of mutant spike proteins “may well occur”, he said.
“But it stops short of providing a concrete link with promotion of blood clotting. Nevertheless, it is certainly something worth investigating further,” Ball added.
Rolf Marschalek, a professor at Goethe University who was involved in the research, said they had been in touch with J&J already, per the Financial Times. “[J&J] is trying to optimize its vaccine now,” he told the FT.
Marschalek said that AstraZeneca had not yet been in touch.
J&J’s vaccine unit, called Janssen, said in a statement to Insider on Thursday: “We are supporting continued research and analysis of this rare event as we work with medical experts and global health authorities. We look forward to reviewing and sharing data as it becomes available, and, currently, we believe it is too soon to draw conclusions.”
An AstraZeneca spokesperson said in a statement to Insider on Thursday: “We are continuing to work with regulators, recommending bodies and the scientific community around the world to understand more about the epidemiology and the possible mechanisms behind these extremely rare events.”
The UK has reported more than 4,000 cases of the variant, which has now spread to 49 countries including the US, according to Global Initiative on Sharing Avian Influenza Data. B.1.1.7, the variant first identified in the UK, remains the most common variant in both countries.
One dose offered far less protection, the Public Health England (PHE) study showed. A single dose of either vaccine was 33% effective against COVID-19 with symptoms caused by B.1.617.2.
The study, which was posted as a preprint Saturday and is yet to be peer-reviewed by other experts, is the first in the world to show that vaccines offer some protection against B.1.617.2, which has mutations that make it highly infectious and potentially able to escape antibodies produced by vaccines.
For comparison, two doses of Pfizer’s vaccine was 93% effective against symptomatic COVID-19 caused by the most common variant in the US, B.1.1.7, and AstraZeneca’s was 66% effective. After one dose, both vaccines were 50% effective against B.1.1.7, the data showed.
Matt Hancock, the UK’s health and social care secretary, said Sunday in a press release that the findings were “groundbreaking” and showed the importance of getting a second dose to secure the “strongest possible protection” against coronavirus variants.
Second shot of Pfizer and AstraZeneca boosted protection
Adam Kucharski, associate professor at the London School of Hygiene and Tropical Medicine, said on Twitter Sunday that “first and foremost” the study was “another reminder that second doses matter.”
The actual amount of protection offered by the vaccines could be more than it seems from the figures, as the PHE researchers did not look at whether the vaccines protected against severe disease caused by variants. COVID-19 vaccines typically offer more protection against these outcomes.
The lower efficacy of AstraZeneca’s vaccine after two doses, compared with Pfizer’s, could be down to the fact that it was mostly given to older people, who have weaker immune responses, the study’s authors said.
The US will send 80 million coronavirus vaccine doses, or 13% of its total supply, abroad by the end of June, President Joe Biden said on Monday. That’s five times more doses than any other country has shared with the world so far.
WHO Director-General Tedros Adhanom Ghebreyesus said last week that wealthy countries had received 83% of the world’s vaccine supply despite making up just 53% of the world’s population. At an event on Monday, Tedros called the situation “vaccine apartheid.”
Biden, too, emphasized the need to share more doses with the world.
“We want to lead the world with our values, with this demonstration of our innovation and ingenuity, and the fundamental decency of the American people,” Biden said at White House briefing on Monday. “Just as in World War II, America was the arsenal of democracy, in the battle against the COVID-19 pandemic, our nation is going to be the arsenal of vaccines for the rest of the world.”
But the US won’t be redistributing doses that might have otherwise gone to eligible Americans.
The US expects to have have enough doses for everyone who’s eligible (people ages 12 and up) within the next six weeks. As of tomorrow, Biden said, 60% of American adults will have already received at least one shot.
The Biden administration’s plan is to allocate 20 million leftover doses of Pfizer, Johnson & Johnson, and Moderna shots to other countries. The US will also donate 60 million AstraZeneca shots – all the AstraZeneca doses the country has produced thus far – overseas.
The Biden administration hasn’t said which countries will receive the new shipments yet, but the US already promised 4 million AstraZeneca doses to Canada and Mexico.
AstraZeneca’s shot is currently being administered in 165 countries. But the US Food and Drug Administration hasn’t authorized the vaccine yet because it’s waiting on the results of a domestic trial, which was delayed for nearly seven weeks in the fall because of an adverse reaction in a UK participant.
The US purchased 300 million doses of AstraZeneca’s shot roughly a year ago as part of its strategy to buy up multiple vaccine candidates before it was known which ones would be effective. By buying lots of different vaccines ahead of time, the logic went, the US would ensure it had doses of an effective vaccine as early as possible.
Before Monday’s announcement, the Biden administration had already pledged to donate the 60 million AstraZeneca doses, but the vaccines still need to pass an FDA safety review before they’re shipped.
The US vaccine rollout is far ahead of other countries
Biden made his announcement at a moment when the US outbreak appears to be turning a corner: For the first time in the pandemic, coronavirus cases are declining in all 50 states. Coronavirus deaths are also at their lowest level since April 2020, Biden said. The CDC reported 415 COVID-19 deaths on Saturday.
But many public-health experts have warned that the US will continue to be vulnerable to future outbreaks if other countries are only vaccinating their populations at low levels. India and Russia, for instance, have vaccinated just around 10% of their populations, while Japan has vaccinated less than 4%.
As long as the coronavirus is spreading, it can mutate – so new variants may continue to arise. Though current vaccines seem to hold up well against existing variants, public-experts worry that a future variant could be far more resistant to vaccine protection.
“We know that America will never be fully safe until the pandemic that’s raging globally is under control,” Biden said on Monday.
Because of this, some experts even think the US should help other countries vaccinate their residents before immunizing its own teenagers.
“To get back to ‘normal,’ we need to immunize our younger people,” Janet Englund, a professor of pediatric infectious diseases at Seattle Children’s Hospital, previously told Insider. But she added that “if we don’t take care of the rest of the world, it’s going to be a temporary fix.”
Describing the results, study author and Oxford professor Matthew Snape told reporters that the side-effects “are more or less the same type of reactions that we’re seeing with the standard schedules, its just that they are occuring more frequently.”
The symptoms went away within 48 hours, Snape said. None of the people in the study were hospitalized, the scientists said.
Snape said that a more fundamental question about vaccine-mixing – whether it gives better protection from COVID-19 – is still unknown.
One suggestion was that vaccine-mixing might lead to short-term practical problems, like people calling in sick to work.
“One of the things its telling us is, for example, is that you wouldn’t want to immune a ward full of nurses with a mixed schedule because you may have higher rates of absentees in the next day,” Snape told reporters.
Severe fatigue and malaise – side-effects serious enough to seek help from a doctor – increased slightly if the vaccine doses were mixed, from about 3% to about 10% for fatigue, Snape said.
But he noted that these are interim results of the study, and that no statistical analysis has been done on the numbers, so the figures should be taken with a grain of salt.
The study was run on participants over the age of 50, and the vaccines were given four weeks apart.
It is possible that the reactions to mixing the vaccines would be more severe in younger groups, which generally get more side-effects, Snape said.
The findings, published as a letter in the peer-reviewed journal The Lancet on Thursday, are the from the Com-COV study.
Future experiments are planned to test whether spacing out the doses to 12 weeks will change things.
By next week, around half the US population will have received at least one coronavirus shot – a milestone that could take other countries years to reach at their current pace.
The pace of vaccinations across the globe remains highly uneven: As of Monday, wealthy countries had received 83% of the world’s vaccine supply, despite making up just 53% of the world’s population, according to World Health Organization director-general Tedros Adhanom Ghebreyesus.
Israel, the US, and the UK have the world’s fastest vaccine rollouts so far. Israel vaccinated half its population in just two months, from December to February, while the UK reached that milestone two weeks ago. In roughly a month, around 75% of the UK could be vaccinated.
Meanwhile, plenty of other countries, including Egypt and South Africa, and aren’t expected to cross that threshold for about a decade at their current pace.
The chart below shows how long it will take 18 countries to reach these key milestones, based on their current vaccine rollout speed.
Epidemiologists have estimated that countries will need to vaccinate around 75% of their populations to reach herd immunity – the threshold beyond which the coronavirus can no longer spread easily from person to person.
For many nations, that’s a far-off goal. At the current rate of 110,000 vaccinations per day, it could take Japan eight months to immunize just a quarter of its population, and more than two years to immunize 75%. South Korea faces a similar predicament: The country’s 75% vaccination threshold is more than a year away.
That means it’s likely to take years to reach herd immunity on a global scale.
Limited vaccine supply has hampered many countries’ rollouts
One of the biggest challenges to reaching global herd immunity is a lack of vaccine supply.
Early in the pandemic, wealthy countries like the US and UK struck deals with pharmaceutical companies – before it was even known whether their vaccines were safe or effective – to buy enough doses for their residents.
Lower-income countries couldn’t afford to make that gamble, so many are still vying for shots or waiting on supply from nations that manufacture doses domestically, like China and Russia.
But even some high- or middle-income nations have had slow vaccine rollouts.
Brazil, for instance, rejected an offer to purchase 70 million doses of Pfizer’s vaccine in August, instead betting on AstraZeneca’s shot (which is significantly cheaper) to drive its vaccination efforts. But Brazil is now running low on vaccine supply, so it’s relying on backup doses of China’s Sinovac shot.
Language from Brazilian President Jair Bolsonaro has also fueled vaccine skepticism. Bolsonaro previously joked that the Pfizer shot could “turn you into an alligator.” On Monday, however, Bolsonaro announced that the government would put an extra 5.5 billion reais ($1.05 billion) toward delivering more vaccines to the public.
In Japan and South Korea, some public-health experts have attributed slow rollouts to consistently low caseloads: Japan’s daily coronavirus cases have never exceeded 8,000, and South Korea’s daily cases have stayed below 1,000 for most of the pandemic. That created less urgency to procure doses quickly.
But there have been other holdups, too: Only doctors and nurses are allowed to administer shots in Japan, and the nation didn’t authorize its first coronavirus vaccine until February, months after the US and UK.
India has also lagged behind in delivering vaccines to the public. Its vaccination effort took a hit when cases began to skyrocket in February, amid the spread of new variants. Healthcare workers had to shift their focus away from administering shots to care for hospitalized patients.
Now, WHO officials are calling on wealthy nations to help other countries pick up the pace.
“COVID-19 has shown that our fates are inextricably linked,” Tedros said in February. “Whether we win or lose, we will do so together.”
Both vaccines are authorized to be given as two injections, spaced weeks apart, but this data again shows how effective the vaccines are overall.
The Korea Disease Control and Prevention Agency (KDCA) said on Twitter Tuesday that one dose of the vaccine co-developed by Pfizer and BioNTech was 89.7% effective at preventing COVID-19 in South Koreans aged over 60. The vaccine co-developed by AstraZeneca and Oxford University was 86% effective at preventing COVID-19 after one dose, it said.
The KDCA analysis included more than 520,000 people who had been vaccinated with a single dose of either vaccine.
The agency didn’t provide a breakdown of how many people received each shot or the severity of illness – COVID-19 vaccines are generally more effective at preventing COVID-19 infections that cause hospitalization or death.
The KDCA said the vaccines’ protective effect was higher when the second vaccination was completed, so a second shot within the recommended period was “absolutely necessary”.
South Korea’s findings adds to a growing body of real-world data suggesting that a single shot of a COVID-19 vaccine protects against COVID-19, but it’s still not clear how long protection from a single dose may last.
Real-world data from the UK, posted as a pre-print study on April 23, found that either Pfizer or AstraZeneca’s vaccine cut COVID-19 infections with symptoms by 72%. Protection from a single dose probably holds up for at least 10 weeks, based on measurements of antibody levels, the study, which wasn’t peer-reviewed, said.
Another real-world study from Scotland published in the Lancet on April 23 found that a single dose of Pfizer’s vaccine was 91% effective against hospitalization at 28 to 34 days following vaccination. One dose of AstraZeneca’s vaccine was 88% effective against hospital admissions after the same time period, the study found.