Getting COVID-19 doesn’t always protect young people from reinfection, study finds

air force members get covid vaccine
Members of U.S. Air Force prepare to receive the first round of the Moderna COVID-19 vaccine

  • Getting COVID-19 doesn’t guarantee protection from reinfection.
  • In one study, around 10% of Marine recruits who previously had COVID-19 were reinfected.
  • Those who had antibodies were about five times less likely to get infected than those who didn’t have them.
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A positive COVID-19 test comes with a tenuous silver lining: you’re protected from the coronavirus, at least for a few months.

But recent research, out today in The Lancet Respiratory Medicine, has found protection from reinfection is not a sure thing.

An observational study of more than 3,000 healthy US Marine recruits revealed that it’s possible for young people to get COVID-19 twice, although those who have had it before have a lower risk of infection.

Around 10% of recruits who previously had COVID-19 were reinfected during a six-week observation period. In comparison, 50% of recruits who had not been previously infected tested positive during the study.

The crowded living conditions of the military bases where the observations took place likely contributed to a higher overall infection rate, but the study authors said the risk of reinfection applies to young people everywhere.

Antibodies provide some protection

Among the recruits – mostly men aged 18-20 – 189 entered the study seropositive, meaning they were previously infected with the coronavirus and had antibodies in their blood.

Most people have an antibody response to infection, where the immune system produces proteins to fight off specific intruders if they return in the future. Antibodies may wane in the months after infection, but the immune system has other protective measures in place.

Commander Andrew Letizia, an infectious disease physician and lead researcher on the study, told Insider the team measured antibodies as proof of previous infection. However, he said some recruits previously tested positive but no longer had detectable antibodies at the time of the study, so the 10% reinfection rate may be an underestimate.

Those who were reinfected with COVID-19 had lower antibody levels compared to those who were previously sick and did not get reinfected.

“Antibodies are certainly protective, but they do not mean that you’re going to be bulletproof,” Letizia said. “You can still potentially get reinfected.”

Reinfection is about one-fifth as likely as a new infection

Based on the study of Marine recruits, the authors concluded that young people who have antibodies are about five times less likely to get infected than those who do not have antibodies. Studies in other populations have produced similar findings.

A preprint study of British healthcare workers, which has not yet been reviewed, found those who had not been previously infected with COVID-19 had a five times higher risk of being infected compared to people who had a past infection.

A study of 4 million people in Denmark found that COVID-19 infection afforded people under the age of 65 around 80% protective immunity after six months. Older people were only 47% protected from reinfection.

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The research is in: People who’ve already had COVID-19 need just one shot

woman receiving covid vaccine
A woman receiving a COVID-19 vaccine in Wales.

  • A single shot of Pfizer or Moderna’s vaccine yields high protection for people who’ve had COVID-19.
  • That’s probably because their bodies are responding to a viral threat they’ve seen before.
  • One expert said giving people who’ve had COVID-19 a second dose was “kind of a wasted shot.”
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In the race to get coronavirus vaccines into arms as quickly as possible, scientists think they’ve found a way to accelerate the process: Give the people who’ve already had COVID-19 just one dose.

Most vaccine-eligible Americans are getting either Pfizer’s or Moderna‘s vaccine, both of which require two doses administered several weeks apart. But a growing chorus of researchers now agrees that a single dose of either vaccine will generate a sufficient immune response among people who’ve already had the coronavirus. Giving them the second dose, research suggests, might essentially waste a good shot.

“For those who’ve been infected and recovered, which is tens of millions of people, they’ll only need one shot, which will make the vaccine go even further,” Dr. James Hildreth, the president of Meharry Medical College, told Insider.

Hildreth served on the Food and Drug Administration advisory committee that recommended all three authorized coronavirus vaccines in the US. The third, from Johnson & Johnson, is a one-shot vaccine, so people who’ve had COVID-19 would get a single dose of that no matter what.

Given that more than 30 million Americans are known to have had COVID-19, that could be up to 15 million Pfizer or Moderna shots that could go to other people.

New research backs up the one-shot strategy

Once a person has had COVID-19, their immune system should recognize the virus if it invades a second time. So when a vaccine spurs the body to start producing antibodies again, it’s logical that the immune system would mount a stronger and quicker defense.

Indeed, a new peer-reviewed study found similar antibody responses among individuals who’d had COVID-19 and received a single dose of Pfizer’s vaccine and individuals who received two doses of the vaccine but had never gotten COVID-19.

The researchers concluded that “a second vaccine dose did not offer previously infected individuals a substantially greater benefit over a single dose.”

After the first dose, nearly 37% of the study participants who’d had COVID-19 experienced significant side effects versus 25% of study participants who’d never had COVID-19. After the second dose, there wasn’t as much difference between the two groups: 51% versus 59%, respectively.

The researchers found that “fever and chills were more common among previously infected vaccine recipients after the first dose, whereas infection-naive individuals were more likely to experience headache, dizziness, or lightheadedness after the second dose.”

‘The first dose ends up serving as the booster’

Vaccine
Registered Nurse Robert Orallo administers the Pfizer Covid-19 vaccine at the Blood Bank of Alaska in Anchorage on March 19, 2021.

In a letter in the New England Journal of Medicine last month, 32 researchers from the Icahn School of Medicine at Mount Sinai wrote that a single-dose strategy for people who’d already had the virus “requires investigation.”

The team found in a small study that people who’d previously had COVID-19 developed 10 to 45 times as many antibodies after their first dose of Pfizer or Moderna’s vaccine as the average uninfected person did. The research is still awaiting peer review.

“The first dose ends up serving as the booster,” Dr. Jeremy Faust, an emergency-medicine physician at Brigham and Women’s hospital, told Insider. “If you’ve been infected, it’s very likely that one dose would be pretty damn good for quite a while.”

There are a few caveats, though: People may need to confirm that they still have antibodies if they were sick a while ago, since antibody levels wane over time. An antibody test would also be required for those who suspect they had COVID-19 but never tested positive. If that antibody test comes back positive, the second shot is most likely redundant.

“What is the point?” Akiko Iwasaki, an immunobiologist at Yale University, told Insider. “It’s kind of a wasted shot.”

‘This is where the policy lags science’

UK testing antibody
A paramedic with a blood sample for a COVID-19 testing program in June.

France in February began recommending a single vaccine dose for people who’ve had COVID-19.

By then, the Mount Sinai research was out, and another preliminary study had also discovered high antibody levels among healthcare workers who’d had COVID-19 before receiving their first shot.

Dr. Mohammad Sajadi, a coauthor of that study, told Insider that COVID-19 patients typically develop antibodies about two to three weeks after their initial infection. But the healthcare workers showed high antibody levels a week after their first shot.

“What that shows you is that individuals who had a prior COVID infection have what we call a recall response or a memory response,” Sajadi said. “For most infections, the second time you see that microorganism, you should get a faster response.”

Then in late February, a UK study found roughly equal antibody levels among people who’d received the first dose of Pfizer’s vaccine and had never gotten COVID-19 and those who’d had COVID-19 but weren’t vaccinated yet. After the people who’d had COVID-19 got their first shot, their antibody levels were 140 times their peak levels before the vaccine.

Yet most countries, including the US, don’t yet recommend a single-dose regimen for people who’ve had COVID-19.

“This is where the policy lags science,” Iwasaki said.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told NBC News in February that the idea was worth considering.

“The data looked really quite impressive – that if you’ve been infected and then you get a single dose, the boost that you get with that single dose is really enormous,” Fauci said. “That is one thing that you might want to consider, but we really want to look carefully at the data first.”

Concerns about long-term immunity

covid vaccine card cdc
An intensive-care-unit nurse, Megan Tschacher, with her vaccination card at UC Health Poudre Valley Hospital in Fort Collins, Colorado, on December 14.

Since scientists haven’t had much time to follow up with vaccine recipients, there’s no consensus yet about how long vaccine-induced immunity lasts. This uncertainty is one reason experts are hesitant to advocate anything other than the standard two-dose regimens of the Pfizer and Moderna vaccines.

Delaying or skipping the second dose places a lot of pressure on the first dose to provide solid, long-term immune protection, Princeton University researchers wrote Tuesday. They expressed concern that switching up the dosing regimen could lead to a “broad range” of outcomes among vaccinated people.

But Iwasaki said people who’d had COVID-19 could probably wait months before getting their second shot – if they need one at all.

“There just isn’t any need to do it so early,” she said.

Scientists are also optimistic that even though antibody levels are known to wane over time, T cells will confer long-term protection for those who’ve had COVID-19. Like antibodies, T cells have impressive powers of recollection that can help the immune system recognize and reattack the coronavirus.

A recent study found that people who previously had COVID-19 mounted a stronger T-cell response to one shot of Pfizer’s vaccine than people who’d never gotten infected did.

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People who had COVID-19 develop strong immunity after a single vaccine dose – so they might need only one shot

vaccine healthcare workers us
A dentist receives the Moderna COVID-19 vaccine on January 8.

  • Two new studies suggest that people who had COVID-19 mount a stronger immune response to their first shot than those who were never infected.
  • Other preliminary studies found that people who already had the coronavirus respond to their first shot the way other people do to their second.
  • So it’s possible some people might need only one shot to sufficiently protect them.
  • Visit Business Insider’s homepage for more stories.

Both Pfizer’s and Moderna’s coronavirus vaccines require two shots: a prime dose, followed by a booster. 

The initial shot should trigger the production of antibodies to the virus for the first time. By the time we get a booster, our bodies should mount an even stronger immune response. That explains why some people have reported more side effects after their second shot.

But for people who’ve already had COVID-19, the process seems to progress differently. An emerging body of research suggests that people who already got a coronavirus infection mount a stronger immune response to their first shot than those who never had the disease. That could mean that people with a history of infection don’t need a second shot to sufficiently protect them from getting sick again. 

A new study from UK researchers found that antibody levels were roughly the same among uninfected people who received the first dose of Pfizer’s vaccine and people who’d had COVID-19 but weren’t vaccinated yet. Then after people who’d COVID-19 got their first shot, their antibody levels were 140-fold higher than their peak antibody levels before the vaccine.

In other words, the prime dose acted more like a booster.

Another new study found that people who previously had COVID-19 mounted a stronger T-cell response to one shot of Pfizer’s vaccine than vaccinated people who’d never gotten sick did. Like antibodies, T cells have powers of recollection that can help the immune system recognize and re-attack the coronavirus.

But the two studies examined only a small group of vaccinated healthcare workers – 123 in total. For this reason, many scientists are wary of prescribing anything other than the standard two-dose regimens.

“I’m a big proponent of the right dosing and right schedule, because that’s how the studies were performed,” Maria Elena Bottazzi, an immunologist at Baylor College of Medicine, told The New York Times.

People who had COVID-19 may develop 10 times as many antibodies after a single dose

thanksgiving travel test coronavirus 2020
Healthcare worker Elizabeth Cameros, right, administers a coronavirus test to traveler Wade Hopkins at LAX on November 23, 2020.

Even before the two new studies came out, preliminary research had started to show that two shots might not be necessary for people who’d already had COVID-19.

In one study, which is still awaiting peer review, researchers at the Icahn School of Medicine at Mount Sinai discovered that people who’d had COVID-19 developed at least 10 times as many antibodies after their first dose as the average uninfected person who received two doses of the Pfizer or Moderna vaccines. 

Those with a history of infection also developed stronger side effects after their first injection – including fatigue, headache, chills, fever, and muscle and joint pain.

The researchers wrote that “changing the policy to give these individuals only one dose of vaccine” could “spare them from unnecessary pain and free up many urgently needed vaccine doses.”

Another preliminary study supports those findings – it showed that healthcare workers who’d had COVID-19 had higher antibody levels after their first vaccine dose than vaccinated healthcare workers who had never been infected.

“It was a very large difference. It was something that we could easily see,” Dr. Mohammad Sajadi, an associate professor at the Institute of Human Virology at the University of Maryland School of Medicine, told Insider.

Typically, Sajadi said, COVID-19 patients develop antibodies about two to three weeks after their initial infection. But it didn’t take nearly as long for the people who’d already been sick to develop antibodies in response to a vaccine: These people showed high antibody levels a week after their first shot, peaking about 10 to 14 days after vaccination.

How long does a ‘memory response’ to COVID-19 last?

covid 19 vaccine drive
Diana Carolina, a pharmacist at Memorial Healthcare System, receives the Pfizer vaccine in Miramar, Florida on December 14, 2020.

Pfizer’s and Moderna’s trials suggested both vaccines are safe for people with a history of coronavirus infection. But there are some exceptions.

The Centers for Disease Control and Prevention recommends that people with an active infection wait until their symptoms have resolved and the standard 10-day isolation period has passed before getting vaccinated. That includes people who’ve already received their first dose.

“The recommendations for receiving any dose of the vaccine are not to get it if you’re frankly ill at the time,” Dr. Sandra Sulsky, an epidemiologist and principal at Ramboll, a global health-sciences consulting firm, previously told Insider.

But scientists still aren’t sure when vaccines are actually necessary for previously infected people. Coronavirus antibodies could last anywhere from several months to several years – but even then, antibody levels don’t always translate to immunity.

All the participants in Sajadi’s study, for instance, tested positive for coronavirus antibodies in July and August. By the time they got their shot, he said, some of them had “very, very low levels” of antibodies, but they still seemed to respond strongly to the vaccine.

“What that shows you is that individuals who had a prior COVID infection have what we call a recall response or a memory response,” Sajadi said. “For most infections, the second time you see that microorganism, you should get a faster response.”

He cautioned, however, that the findings apply only to people with a “run-of-the-mill COVID infection” – people who developed antibodies and have recovered from their illness.

An interim solution to limited doses

COVID Vaccine Line
People waiting in line in a Disneyland parking lot to receive COVID-19 vaccines.

Sajadi said that giving just one dose to people who’ve already had COVID-19 could help address vaccine shortages. So far, just 47 million Americans vaccinated, with the majority of adults still waiting.

“In times of vaccine shortage, where every vaccine dose counts, we think the data shows if you had previous COVID infection, you may only need one dose for the booster,” Sajadi said. That “may even be the ideal scenario” for previously infected people, he added.

The CDC has said vaccination sites can delay administering a second dose for up to six weeks – instead of the recommended three to four weeks – in “exceptional circumstances.” 

It is not yet known how antibody levels among people who’ve had COVID-19 will change in response to to Johnson & Johnson’s shot. That vaccine expected to get authorized for emergency use in the US within days.

“There’s no reason to think it would act differently,” Sajadi said. “But you just never know until you test.”

This story has been updated with new information. It was originally published on February 2, 2021.

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Elon Musk set up a COVID-19 antibody study at SpaceX and got 4,300 employees to take part, according to reports

elon musk space x SpaceX Chief Engineer Elon Musk speaks in front of Crew Dragon cleanroom at SpaceX Headquarters in Hawthorne, California on October 10, 2019. (Photo by Yichuan Cao/NurPhoto via Getty Images)
SpaceX CEO Elon Musk.

  • Elon Musk’s company SpaceX has been regularly testing a group of employees for COVID-19 antibodies.
  • 4,300 employees signed up for a study looking at possible links between antibodies and immunity.
  • “People can have antibodies, but it doesn’t mean they are going to be immune,” said one of the study’s authors.
  • Visit the Business section of Insider for more stories.

Elon Musk’s space exploration company SpaceX has been using its employees to run a COVID-19 antibody study, The Wall Street Journal reported Saturday.

The results of the study were made public in a peer-reviewed paper published in Nature Communications, which lists Elon Musk as a co-author.

According to the study, SpaceX sent an email round to staff asking for volunteers to participate in a regular antibody study to study COVID-19. After that email was sent, 4,300 SpaceX employees signed up to give monthly blood samples so they could be tested for antibodies.

According to the Journal, Musk and SpaceX’s top medical executive Anil Menon worked to bring on various doctors and academics to design the study.

The published study includes data spanning from April – when the testing  started – and June, although regular testing is still ongoing according to the Journal.

The study provides more information in the ongoing efforts to understand how COVID-19 works, and whether a certain number of antibodies could provide a level of immunity.

The study’s findings suggest that people who had only mild COVID-19 symptoms developed fewer antibodies, which might mean they are less likely to have long-term immunity and could therefore get reinfected.

Researchers still working on the study told the Journal they have already observed some instances of reinfection in workers who previously were found to have low numbers of antibodies.

“People can have antibodies, but it doesn’t mean they are going to be immune,” Dr. Galit Alter, one of the study’s co-authors and a professor of medicine at Harvard Medical School, told the Journal. “The good news is most of the vaccines induce [antibody] levels way higher than these levels,” Dr. Alter added.

Scientists are still researching whether catching COVID-19 provides any form of lasting immunity.

Dr. Alter also told the Journal Elon Musk took a personal interest in the research and had the study’s authors brief himself and SpaceX executives on how vaccines and antibodies work.

SpaceX was able to repurpose medical facilities it had already set up before the pandemic, and recruited interns from nearby hospitals to help draw the volunteers’ blood. Out of 4,300 volunteers 120 who tested positive for COVID-19 had their blood carefully examined to see how many antibodies they’d produced. Out of this 120, 61% reported no symptoms.

Out of that 120-strong sample 92% were male and the median age was 31. The larger sample was 84.3% male with a median age of 32 – although the age range spanned from 18 to 71.

Elon Musk himself said he’d tested positive for coronavirus in November last year, and in the early months of the pandemic the billionaire repeatedly vented his frustration at lockdown measures calling them “fascist.” At one point he defied a shelter-in-place order to open his Tesla factory in Alameda County, California, – after which several employees tested positive for coronavirus.

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