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For those who have postponed their vaccination because they have already been infected with the coronavirus, a growing body of evidence suggests that vaccination and natural immunity lead to particularly robust protection, including against variants of the virus.
So-called hybrid immunity – that is, natural immunity against infection combined with immunity provided by the vaccine – appears to result in stronger protection than simple infection or vaccination alone.
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“There really is this dramatic increase in immunity in people who have already been infected if they receive at least one dose of the vaccine,” said Shane Crotty, professor of immunology at the La Jolla Institute of Immunology. in California.
“Against some of the more concerning variants, it’s literally 100 times better antibody levels after vaccination compared to before for someone with natural immunity,” Crotty said. “It’s not a small change.”
Fikadu Tafesse, assistant professor of molecular microbiology and immunology at Oregon Health and Science University, agreed. Tafesse’s research found that vaccination resulted in increased levels of neutralizing antibodies against variants of the coronavirus in people who had previously been infected.
“You will get better protection by also getting the vaccine compared to just getting an infection,” he said.
Although a previous case of Covid-19 confers some degree of immunity, the level of protection can vary, leaving some people vulnerable to reinfection.
“Antibody levels are really variable after recovering from infections, and those on the lower end of the spectrum might be more susceptible to re-infections,” said Deepta Bhattacharya, professor of immunology at the University of Arizona. “But after just one vaccine in people who have recovered from Covid-19, antibodies are skyrocketing, including those that neutralize the worrisome variants. ”
In a study published on the BioRxiv preprint server, researchers at Rockefeller University in New York City examined how different types of immunity would protect against potential variants. (The studies published on the preprint servers were not peer reviewed.) To do this, they designed a modified version of the coronavirus spike protein with 20 naturally occurring mutations to test how antibodies would work against it.
These modified spike proteins were tested in lab boxes against antibodies from people who had recovered from Covid-19, those who had been vaccinated and those who had hybrid immunity. The spike proteins were able to escape the antibodies of the first two groups, but not the antibodies of people with hybrid immunity.
Another study, conducted by researchers at the Centers for Disease Control and Prevention, found that among those who had previously been infected, vaccination reduced the risk of re-infection more than twice, compared to natural infection alone.
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The immunological benefit of hybrid immunity, according to Crotty, comes in part from what are called memory B cells: immune cells that produce the antibodies that fight the virus.
“Memory B cells are basically antibody factories with the lights off,” Crotty said. “If the virus gets past your first line of defense, which are the circulating antibodies, memory B cells can turn on and make more antibodies.”
These cells are trained to produce antibodies against specific threats – like the coronavirus – after being first exposed to the threat. But memory B cells don’t just make antibodies that worked in previous infections; these cells also constantly change the formula, producing antibodies that could target virus variants that may not yet exist.
Vaccine-induced immunity and natural infection activate the antibody-generating abilities of memory B cells. But research has shown that memory B cell levels are, on average, higher in people with hybrid immunity compared to natural infection or vaccination alone.
This could contribute to the wider spectrum of antibodies seen in people with hybrid immunity.
These antibodies “recognize all of these things that other people just don’t recognize,” Crotty said.
This recognition may go beyond variants of the virus that causes Covid-19: hybrid immunity antibodies may also recognize the original 2003 SARS virus, according to a study published in June in the journal Science.
The results give Crotty hope that a vaccine against all coronaviruses is a possibility in the future.
“You could really have a vaccine that could recognize a range of current and future coronaviruses, which is not just a daydream,” he said. “The data carrier that is truly possible. ”
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