A new U.S. study suggests people who received mRNA vaccines are potentially protected against the coronavirus for years — or even a lifetime.
The study, published Monday in the journal Nature and led by Washington University immunologist Dr. Ali Ellebedy, found the Pfizer vaccine triggered a persistent immune response that could offer long-time protection from the coronavirus.
Scientists from the Washington University School of Medicine, Icahn School of Medicine at Mount Sinai in New York City, and the University of Texas Medical Branch, examined the immune response of people who received two doses of the Pfizer vaccine, by collecting blood samples from 41 participants and draining lymph nodes from 14.
Ellebedy’s team found that nearly four months after the first dose of the vaccine, the germinal centre was still highly active and the number of memory cells that recognized the coronavirus had not decreased. The germinal centre is where long-lived antibody-secreting plasma cells and memory B-cells are made; both important in providing protection against reinfection.
Although it is still early days in studying the effects of COVID-19 vaccines, experts in Canada contacted by the Star for their views on the research were enthusiastic about the results.
“The reason this paper is very exciting is because the more B-cells that you have, that are specific to the vaccine, the longer we think your protection lasts,” said Dr. Dawn Bowdish, an associate professor of pathology and molecular medicine at McMaster University, who, like the other experts interviewed, was not involved in the study. “The excitement here was just the sheer number of these B-cells that are in your lymph nodes producing these antibodies.”
The study adds to other recent research, which suggests individuals who received mRNA jabs (which include Pfizer and Moderna) may not need booster shots, and that those who were previously ill and recovered from COVID-19 before vaccination may not need a booster even if new variants emerge. However, the findings are dependent on the virus and its variants not evolving enough to bypass immunity.
In May, Ellebedy and his colleagues published another paper which found that individuals who survived COVID-19 retained immune cells in their bone marrow that recognized the virus for at least eight months after infection.
Another study published June 14 in Nature found those same memory cells continue to mature for at least a year after infection. The data suggests immunity in recovering individuals “will be very long-lasting,” and if they receive mRNA vaccines, they will produce antibodies and memory cells that should be protective against circulating variants.
But “nobody can predict how long-lasting [vaccines] can be,” Bowdish said. “None of us can predict the future.”
For example, people who are immunized against tetanus may have high counts of B-cells and antibodies, and “it could be inferred they would be protected forever,” she explained. In fact, they would be protected between 10-12 years, which is why a tetanus booster is administered after a decade.
When an individual receives a vaccine or is infected, parts of the virus break off and make their way to a newly formed structure called the germinal centre, which can be located in lymph nodes, explained Omar Khan, a biomedical engineering professor at the University of Toronto. There, they “stick” to B cells, which recognize they need to create antibodies to fight the virus.
The B-cells begin cloning themselves, and create antibody-secreting B-cells called plasma blasts. Over the next two weeks, antibodies are refined in the germinal centre to become more specific and targeted, to generate a better immune response.
Ultimately, B-cells send versions of themselves, which travel to the bone marrow, becoming a plasma cell. In the bone marrow, the plasma cell makes antibodies for the rest of a person’s life at low levels.
“If you see that, you definitely know you have long-term immunity,” said Khan.
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Back in the germinal centre, some B-cells remain. They retain memory and can reactivate much faster in case of danger, like reinfection or another jab.
Plasma cells eventually die, to be replaced with new plasma blasts from memory B-cells in lymph nodes.
“This study has shown the first really interesting clues that say we are developing this long-term memory,” said Khan. “It’s fantastic … it makes us all super excited.”
While boosters may not be necessary for lifelong protection, they’re important during a pandemic, when people are facing imminent exposure to the virus and maintaining high antibody levels offers extra security, Khan said. If global infection rates are high, it gives the virus opportunities to replicate, and with every replication there’s a chance of a mistake and mutation, he added.
“If the coronavirus gets to mutate so much … and there’s a newer version, that’s just different enough to where antibodies aren’t as efficient, then we don’t get as much protection,” he said. Part of the reason for the boost is to maintain a high enough concentration of antibodies to overcome the loss of efficiency.
Bowdish said scientists predict about 20 mutations in the virus are required to escape our entire immune response to vaccination.
“There are some variants in the world that have 10 of those 20 mutations … it’s not impossible that we’re going to need boosters in the future to deal with the Delta variants or others that are going to emerge,” she said.
People get the flu shot every year because the influenza virus changes, Bowdish added.
“It’s pretty fair to say that people will probably have a good lasting immune response to the virus we were all vaccinated against. However, if there’s a new variant that escapes that, then we’re back to needing a booster shot again.”
Dr. Eleanor Fish, professor of Immunology at the University of Toronto, noted in an email to the Star the participants in the U.S. study were mainly healthy young adults, with a median age of 37. It’s “unlikely” at this point in time that a blanket statement can be made there will be no need for booster vaccinations due to a lifetime of protection, she wrote. Variables like age, sex, gender, co-morbidities are all factors that contribute to how robust an individual’s immune response to vaccination will be.
Meanwhile, early findings of a new U.K. study exploring the efficacy of receiving a dose of the Pfizer vaccine four weeks after a dose of the AstraZeneca vaccine suggest the mix produced a significantly stronger immune response than two doses of the AstraZeneca. The data follows other studies conducted in Germany and Spain with similar results.
The U.K. researchers assessed four vaccine combinations; two doses of the Pfizer, two of the AstraZeneca, a first dose of the AstraZeneca followed by Pfizer and a first shot of the Pfizer followed by the AstraZeneca.
They found that mixing created the strongest immune response, but the highest antibody response was generated by two doses of the Pfizer.
The National Advisory Committee on Immunization in Canada released updated guidance June 17, stating it is “preferred” every Canadian whose first dose was AstraZeneca follow it with an mRNA vaccine of Pfizer or Moderna for their second dose.
Maria Sarrouh is a Toronto-based staff reporter for the Star. Reach her via email: [email protected]
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