It was great news: From January to April, just 0.01% of vaccinated Americans – around 10,000 out of 100 million people – got breakthrough infections, or cases of COVID-19 diagnosed after they were fully immunized.
That’s according to a report from the Centers for Disease Control and Prevention, which also indicated that certain coronavirus variants were to blame for most of these breakthrough cases. However, the CDC only had genetic sequencing for around 5% of the post-vaccine infections, and the report didn’t include data about the Delta variant. That strain, first detected in the US in March, might pose the greatest challenge to vaccine efficacy.
But before more data could be collected to answer these lingering questions, the CDC stopped tracking breakthrough infections that resulted in asymptomatic, mild, or moderate cases. Since May 1, the agency has only reported and investigated coronavirus infections among vaccinated people that resulted in hospitalization or death.
Sequencing efforts in the US haven’t ramped up much, either: The country is still only sequencing about 1.4% of its coronavirus cases, according to data from GISAID, a global database that collects coronavirus genomes.
That means it’s difficult to tell exactly how much of a risk the Delta variant poses to vaccinated people. Researchers still don’t know whether Delta makes breakthrough cases more common, or what the typical symptoms of a breakthrough infection caused by Delta look like. As a result, vaccinated people may have a hard time weighing the risks of returning to normal social activities or knowing what to expect should they develop a rare breakthrough case.
“By tracking only cases requiring hospitalization or causing death, we may miss the chance to learn how people with ‘milder’ disease are affected by Delta or other variant infections, such as how long their symptoms last and how the infection may disrupt their lives,” Shmerling told Insider.
He added that the US could also miss important information about which vaccines are most effective against Delta, how long vaccine protection against the variant lasts, and whether the timing of a second vaccine dose might determine one’s likelihood of a breakthrough case.
The CDC told Insider that in a substantial proportion of reported breakthrough cases, data on symptoms is missing, “which is one reason why CDC is publicly reporting hospitalized and fatal cases.”
The agency added that its Emerging Infections Program is still working with nine states to obtain sequencing data from breakthrough cases – including asymptomatic and mild ones.
How well do vaccines protect against Delta?
So far, data suggests that vaccines hold up extremely well against Delta: Public Health England analyses have found that two doses of Pfizer’s vaccine are 96% effective at preventing hospitalizations in cases involving the variant, and 88% effective at preventing symptomatic illness. Two doses of AstraZeneca’s vaccine, meanwhile, are around 92% effective at preventing hospitalizations and 60% effective at preventing symptomatic COVID-19 from Delta.
Moderna announced on Tuesday that its vaccine is also highly effective against Delta based on lab studies, though the efficacy was slightly diminished compared to the original strain. And South African researchers recently found that among people who’d received the Johnson & Johnson vaccine, 94% of breakthrough infections were mild – including those caused by Delta.
However, Public Health England found that one shot of either Pfizer’s or AstraZeneca’s vaccines was just 33% effective at preventing symptomatic COVID-19 from Delta. Israeli health officials also reported last week that as many as half of new COVID-19 cases in Israel are among vaccinated people, with the majority of cases being driven by the Delta variant. (However, vaccinated people in Israel appeared to develop milder cases than unvaccinated people.)
Shmerling said that finding out which variants are responsible for most breakthrough cases – whether it’s Delta or another strain – could help vaccine manufacturers learn whether they need to modify their current shots or roll out boosters more quickly.
“It’s possible that tracking the severe cases would give us enough information about which variants are responsible for most breakthrough infections,” he said. “But, again, the more we know about all breakthrough cases, the better we’ll understand how they occur.”
Anna Kern got her second vaccine dose five months ago, but it wasn’t a ticket to normalcy. Kern, a 33-year-old nurse practitioner, tested positive for COVID-19 in April and has been struggling with long COVID ever since.
The post-viral illness is characterized by symptoms that last a minimum of three weeks, but can often drag on for months. Kern said her symptoms have gotten steadily worse. At first, she had chills and felt run-down, so she cut back her work hours – Kern had been doing COVID-19 tests in the Detroit area. Then she started experiencing extreme fatigue after minor activities like a walk or jog.
In May, Kern recorded her heart rate while going about her morning routine – eating breakfast, brushing her teeth, washing the dishes. She was at 130 beats per minute, a rate she’d normally only hit through exercise. Symptoms like racing heart and fatigue are commonly reported among people with long COVID, who are also known as “long-haulers.”
By Memorial Day, Kern could barely move after working a shift.
“I remember waking up and knowing that I needed to drink some water and maybe eat some food, but being so tired that I was trying to figure out if I could actually do that,” she said. “I ended up crawling from my bed to my refrigerator.”
She considered asking for more time off, even though she was working remotely. But around the same time, she learned that her nursing position – her main source of income – had been cut.
With her life upended, Kern turned to a long-haul support group in search of others like her. She found a few people who’d also gotten breakthrough infections – cases of COVID-19 diagnosed at least two weeks after someone is fully vaccinated – and still hadn’t recovered. But not many.
For now, there’s no good data to assess how common long-haul cases are post-vaccination, but the chances of getting any breakthrough infection are rare. A May report from the Centers for Disease Control and Prevention found that just 1 in 10,000 vaccinated Americans got sick after their shots. And UK researchers estimated last year that long-haul cases can occur in around 10% of people diagnosed with COVID-19.
So the chances of getting long COVID after being fully vaccinated is “a low probability times a low probability,” Bob Wachter, chair of the Department of Medicine at the University of California, San Francisco, told Insider.
Still, he said, “I’m at the stage now where I’m quite confident it can happen. I really doubt it’s going to turn out to be one in a million.”
‘You feel lots of guilt – like, what did I do wrong?’
Kern’s job put her at high risk of a coronavirus infection before her vaccine, so she donned full protective equipment during her shifts.
“Before I went into my apartment, I would like take off my clothes and put my scrubs in a bag and take bleach water and rubbing alcohol and wipe down everything that I was bringing inside,” Kern said. “I wasn’t even taking a coat in April of last year, even though it was kind of chilly, because I didn’t want to have to deal with it afterwards.”
Then she got her first Pfizer shot in December.
“It felt like relief flooding through my body – like, OK, I’ve survived,” Kern said.
But four months later, an unvaccinated coworker got sick. The woman wasn’t diligent about wearing her mask, according to Kern.
Less than a week later, Kern started feeling fatigued. She thinks the vaccine helped prevent a more severe outcome, but she still wonders whether she slipped up somehow.
“You feel lots of guilt – like, what did I do wrong? How could I have been more cautious?” she said.
Of course, no coronavirus vaccine is 100% effective – and even the shots from Moderna and Pfizer appear to be slightly less effective in the face of new variants.
“The chances of a breakthrough infection are real,” Wachter said.
He added that even people who get relatively mild cases post-vaccine can feel crummy for several months – “and maybe for years, we just don’t know.”
Kern said she’s having a hard time trusting that it’s safe to return to normal activities. She worries she won’t be feeling up for work any time soon.
“I have been pretty much working nonstop since COVID started,” she said. “This wouldn’t have been the way that I would have elected to take some time for me to breathe, but it is the way that it’s happening.”
Karlee Camme was supposed to see her grandparents for the first time in over a year. Everyone was fully vaccinated and ready to go, but two days before the visit, she lost her ability to taste and smell.
Looking back, she realized the runny nose and heavy tiredness she’d experienced earlier in the week may have been early symptoms. It was only the loss of taste and smell that signaled it was anything more than a common cold, leading Camme to get a COVID test.
The COVID-19 vaccines have been extremely successful at preventing serious illness that could lead to hospitalizations and deaths. But no existing vaccine is 100% effective at preventing infection, Dr. Lisa V. Adams, associate dean for global health at Dartmouth College, told Insider.
“We know there are and will be some breakthrough infections in individuals who are vaccinated – at least until we get to a point where there is very little virus circulating,” Adams said. “The good news is that their illness should be very mild.”
The vaccines are meant to prevent hospitalizations and deaths
Out of more than 95 million fully vaccinated Americans, less than 0.01% of them got breakthrough infections, the CDC reported at the end of April. That includes at least 594 hospitalizations and 112 deaths related to COVID-19.
Around half – 45% – of breakthrough infections occurred in people aged 60 and older. That includes cases in nursinghomes, where residents and staff were among the first Americans to get vaccinated. Elderly people with preexisting conditions may be prone to more severe illness, and transmission is more likely to occur in congregate living settings.
Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, told Insider that even with a smattering of breakthrough infections taken into account, the vaccines have met the goal of protecting most people from severe illness.
“The goal of these vaccines is to keep you out of the hospital and keep you out of the ICU and keep you from dying,” Offit said. “If you have a mild infection where you’re PCR positive and have essentially an asymptomatic infection, that’s fine.”
Breakthrough cases may cause some symptoms, but they’re usually mild
Some breakthrough infections are so mild they may as well be asymptomatic. Camme, for instance, was not sick enough to suspect she had COVID-19 at first.
Masha Gessen, 54, a staff writer for the New Yorker, also got sick despite being fully vaccinated. Her illness was fairly mild, she wrote for the magazine – her symptoms included a runny nose, itchy eyes, fatigue, and loss of smell.
Gessen recovered in about a week, which seems to be the case for most people with mild breakthrough infections.
An article in the New England Journal of Medicine described two similar cases that both resolved within a week or less after testing positive: a 51-year-old woman who had a sore throat, congestion, headache, and loss of smell; and a 65-year-old woman who was also congested, fatigued, and headachy.
The worst of Camme’s symptoms started a week after she tested positive. She noticed she felt winded walking from her car to work, stopping to catch her breath. She’s also been nauseous and has had migraines, chills, and night sweats for nearly a month since her COVID test.
Breakthrough infections may be less contagious to others
Even though Camme is still experiencing some symptoms due to her breakthrough infection, she sees a silver lining in the fact that she didn’t pass the virus to her loved ones.
“My partner didn’t even get the vaccine and he didn’t get the virus, and we were sleeping in the same bed until I tested positive,” Camme said. “That’s the thing – you may still get it, but the chance of you having to feel guilty about spreading it is a little bit less.”
People who get COVID-19 despite being fully vaccinated typically have much less virus in their systems, meaning that they may be less contagious to others, Israelistudies have found. The articles have yet to be peer-reviewed, but the findings are promising.
More studies from Israel have also shown that the Pfizer vaccine may be 94% effective at preventing asymptomatic infections, which reduces the risk of someone unknowingly transmitting the virus.
Vaccinating the majority of people is key to stopping infections
To entirely eliminate the risk of getting COVID-19, more people need to get vaccinated, Offit said. He estimated that 80% of the population needs to be immunized – either through vaccinations or natural infections – to get the US out of the woods.
“This virus is going to be with us for a while,” Offit said. “But the goal is to control spread, which I think we’re gradually doing.”
Even after her breakthrough infection, Camme maintains a positive attitude and faith in the vaccine.
“I’m an advocate for the vaccine,” she said. “The only way that we’re going to get through this is if everybody or majority of the population gets vaccinated. I think that’s the only step forward that we can take to being a more normal world again.”
Most recently, the Minnesota Department of Health identified 89 “breakthrough” infections in people who got two doses of the Pfizer or Moderna vaccine or one dose of the Johnson & Johnson vaccine.
More than 800,000 people have been fully vaccinated in Minnesota to date, putting the breakthrough rate at around 0.01%.
“That’s well below one tenth of one percent – an incredibly small number of cases that dramatically illustrates how effective these vaccines are,” state infectious disease director Kris Ehresmann said in a briefing Wednesday.
Fully vaccinated people are less likely to get severe COVID-19
Although a small number of fully vaccinated people do get infected with COVID-19, they’re likely to have milder cases than they would’ve had they not gotten the vaccine.
Some breakthrough cases in Minnesota required hospitalization, but their outcomes were better overall, Andrew Olson, director of hospital medicine at M Health Fairview, told AP News.
None of the 89 fully vaccinated Minnesotans who tested positive for COVID-19 have died, Ehersmann said in the briefing Wednesday.
“It’s important to know that even if someone is vaccinated and then goes on to be one of the few unfortunate people to develop a breakthrough case, there still can be some level of protection provided by the vaccine,” she said.
When we reach herd immunity, breakthrough cases will be even less common
Breakthrough cases are not a reason to doubt vaccine effectiveness, Ehersmann said in the briefing. Health officials weren’t shocked that some vaccinated people tested positive for COVID-19; in fact, they were pleasantly surprised that the case rate for that group was so low.
Even if a small number of vaccinated people do get sick, their vaccinations bring the country closer to reaching the herd immunity threshold, where the people immune to the coronavirus will outnumber those who are not protected.
“At that point, the virus will not be able to find the small number of people who remain susceptible, either because they didn’t get vaccinated or because they didn’t have a strong enough immune response to the vaccine,” Ehersmann said.