Post-vaccine infections: Why you should not worry about re-infection after getting COVID-19 vaccine

Re-infection after getting Coronavirus Vaccine or maybe New Covid variant is capable of dodging the immune response but in the long term, the outlook is good, say experts.

According to the latest figures released by the Centers for Disease Control and Prevention (CDC), of the more than 87 million people vaccinated in the US as of April 20, 7,157 (0.008%) have been infected with SARS-CoV-2.

The real numbers are likely to be slightly higher because mild or asymptomatic infections may go undetected. But the data is still encouraging.

Only a small fraction of the vaccinated people were infected, and the part that became seriously ill was even smaller: only 331 cases were hospitalized from COVID-19 and 77 died from the disease.

The latest published studies show that even in high-risk settings such as nursing homes, post-vaccine infections seem rare. And if they do occur, the symptoms are usually mild or nonexistent. Also, vaccinated people who become infected have lower viral loads than unvaccinated people, and that means they are less likely to transmit the virus.

Even so, it is important to continue controlling the infections of those vaccinated. All existing COVID-19 vaccines prepare the immune system to recognize the spike protein on the surface of the virus so that when the system encounters the real pathogen, it can quickly fight back. But if the body does not generate a strong immune response to the vaccine, it will not be ready to fight the virus. In other cases, the pathogen may have evolved enough to bypass the immune response prepared by the body, and the vaccine will not work as well. This is called a viral escape from the immune response.

Some coronavirus researchers are concerned that, with so many viruses circulating around the world, SARS-CoV-2 increases its chances of finding a winning combination of mutations that allows it to escape the immune response elicited by the vaccine. Tracking the infections of those vaccinated could help detect new variants of concern and identify when vaccines are becoming less effective. This could determine when booster injections are needed or point to more effective vaccine designs.

High risk settings

People who work and live in nursing homes were the first to receive the COVID-19 vaccine. Between the end of December and the end of March, the number of cases in these facilities fell by 96%. These are ideal places for pathogens to spread, and where vaccines probably won’t work as well because older people’s bodies tend to generate a weaker immune response. Even flu outbreaks can be deadly in these centers. But the CDC found few COVID-19 infections after vaccination.

In one study, researchers analyzed infections in 78 nursing homes in Chicago with almost 8,000 vaccinated residents and 7,000 vaccinated employees. They found more than 600 coronavirus infections, but only 22 of them occurred in fully vaccinated people, 12 in residents, and 10 in staff.

Fourteen were asymptomatic and five had only mild symptoms. When the team examined samples from seven of the people with post-vaccine infections, they found low levels of the virus. And none of the initial infections resulted in additional cases, suggesting that vaccinated people did not spread the virus.

And when outbreaks do occur, vaccines still provide good protection. A second CDC study examined an outbreak in a Kentucky, US, senior center where only half of the staff were fully vaccinated. The outbreak, which began with an unvaccinated staff member, led to 46 COVID-19 infections. Of the 71 residents vaccinated, 18 of them (25%) became infected, two were hospitalized and one died. In the case of the staff, the situation was better. Of the 56 vaccinated employees, four (7%) were infected. Most of these infections were asymptomatic. Only 6.3% of vaccinated residents and staff developed symptoms, compared to 32% of unvaccinated people.

During an outbreak in a nursing home, “staff and residents continually encounter the SARS-CoV-2 pathogen over and over again,” says the infectious disease model maker at the University of California School of Medicine in Maryland Meagan Fitzpatrick. Therefore, it is encouraging to see such a low number of infections in these types of settings.

Monitor variants

The new studies also suggest that variants may be blamed for some of these post-vaccination infections. Viral variants are “one of the unpredictable factors,” said the US President’s top medical adviser, Anthony Fauci, in a briefing on April 12. Although there is little real-world data, laboratory studies suggest that at least some of the variants are less susceptible to vaccine-induced antibodies than the original SARS-CoV-2.

In the Kentucky study, researchers found that the outbreak was caused by the variant known as R1 or South African, which had not been previously identified in that state. This virus had several important mutations that had also been identified in other variants.

For example, the E484K mutation, which is also found in the B.1.351 variant first identified in South Africa, appears to help the virus bypass the antibody response. And the D614G mutation could increase transmissibility. The authors note that although vaccination reduced the likelihood of infection and symptomatic illness, the virus managed to infect more than a quarter of vaccinated residents and approximately 7% of staff.

That suggests the vaccine might not work as well against this variant, but the authors caution that the study was small. (The Chicago authors did not sequence the virus.)

A New England Journal of Medicine study looked at infections in Rockefeller University staff in New York. Between January 21 and March 17, researchers tested 417 employees who had received both full doses of the vaccine from Pfizer or Moderna. Two women tested positive. When the researchers sequenced the viruses, they found that each was a slightly different variant and that they did not exactly match any of those previously identified.

One woman, for example, had a variant with the mutations found in B.1.1.7, which originated in the United Kingdom, and with the mutations common to B.1.526, which originated in New York City. “She had variants somewhere between the two,” says the Rockefeller University physician and biochemist and lead author of the study, Robert Darnell.

When a post-vaccine infection occurs, it is assumed that the person failed to generate a strong immune response to the vaccine, explains Darnell. But that didn’t seem to be the case for this woman. Darnell was able to get her blood sample shortly after testing positive. He and his colleagues found high levels of antibodies capable of neutralizing SARS-CoV-2. Since she was newly infected, the response of those antibodies was probably due to vaccination, not her recent infection, because the antibodies take a while to develop.

It’s not entirely clear why her immune system didn’t protect her from infection, but one possibility is that this variant managed to dodge her response. Stephen Kissler, Harvard University School of Public Health epidemiologist TH Chan, explains:

“For this particular patient, that’s probably the best explanation for what we saw. It’s not surprising to me that a lot of these breakthrough infections that we’re seeing are from variants.”

As more and more people get vaccinated, “there’s an evolutionary selection pressure that’s being applied,” he adds.

On the other hand, as more people are vaccinated, we will see fewer infections and the virus will have fewer opportunities to mutate. And Fitzpatrick points out that even if the viral escape of the immune response explains that woman’s infection, it is but a case. And there is no evidence that she transmitted the infection to other people who had also been vaccinated. The phenomenon is worthy of further study, but Fitzpatrick adds: “I don’t yet see this as alarming. There’s not yet a public health crisis.”

And even when these post-vaccine infections do occur, it does not mean that the vaccine has failed, says Monica Gandhi, infectious disease doctor at the University of California, San Francisco. Antibodies are only part of the immune response. T cells also have a very important role, activating other parts of the immune system and eliminating the virus after infiltrating the body. They do not prevent infection, but they can slow the spread of the virus. And some research suggests that the body’s T-cell response is much harder to bypass. “You may actually get a mild infection, but hopefully you’ll still have protection against severe disease,” says Gandhi.

Even so, it is important to keep track of the infections of those vaccinated to look for unexpected changes. An increasing number of infections in vaccinated people could mean a decrease in immunity or the appearance of a new variant capable of dodging the immune response. Vaccines may need to be modified and we will probably need booster shots. But over time, Kissler concludes:

“our bodies will develop a more complete immune response. And even if we do get reinfected, we’ll be protected from the most severe outcomes. In the long term, the outlook is good.”

This article was published by Technology Review.

Image Credit: GettyImages

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