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For people who have had Covid-19, a single dose of the Pfizer vaccine is enough to provide robust protection against the coronavirus, according to two new British studies published Thursday night in The Lancet, a leading medical journal.
The studies, among the first fully approved papers to weigh in on how to vaccinate people who have had Covid-19, have added strong evidence in favor of inoculating people who already have antibodies to the virus – but only with one dose of Pfizer vaccine.
One of the studies, led by researchers at University College London and Public Health England, described the benefits of this strategy.
“This could potentially speed up vaccine deployment,” they said. And that in turn could prevent dangerous new mutations: “Wider coverage without compromising vaccine-induced immunity could help reduce the emergence of variants,” the newspaper said.
In recent weeks, several studies on the subject have come online and have not yet been published in scientific journals, showing that a dose of a vaccine against the coronavirus amplified the antibodies of people with a previous infection.
People’s immune responses to infection vary widely: most people produce large and long-lasting antibodies, while others who have had milder infections produce relatively little, making it difficult to know how much. they are protected against the virus.
The vaccines act as a kind of booster for these people’s immune responses, inducing enough antibodies to provide protection. But a single dose, rather than the full two-dose protocol, is sufficient for those who have been infected, a number of studies have suggested.
Some researchers in the United States are trying to persuade the Centers for Disease Control and Prevention to recommend giving only one dose to people who have recovered from Covid-19. British studies seem likely to pressure health officials to consider the same approach.
More than 28 million people in the United States and four million people in Britain, as well as many others whose disease has likely never been diagnosed, have been infected so far.
One of the new studies – led by Charlotte Manisty, professor at University College London, and Ashley D. Otter, researcher at Public Health England – followed 51 health workers in London who underwent routine tests for antibodies and infection since March. . This gave researchers an unusually detailed picture of any pre-existing protection against the virus.
About half of the health workers had suffered from a mild or asymptomatic infection. And a single dose of the Pfizer vaccine increased their antibody levels more than 140-fold from their peak levels before they were inoculated, according to the study. This appeared to give them better protection against the coronavirus than two doses of the vaccine in people who had never been infected, the researchers wrote.
The study sparked the idea of doing blood tests on people in the weeks before they were eligible for a Pfizer vaccine to determine if they already had antibodies. People’s immune responses to infection are highly variable, making it difficult to predict without a blood test that can be fully protected with just one dose.
As another benefit of the single-dose strategy, the researchers wrote that it would spare people who have already been infected from the nasty side effects that sometimes follow a booster shot in this group.
The second study, led by scientists at Imperial College London, measured the immune responses of 72 health workers who were vaccinated in late December. A third showed signs of infection.
For these people, a dose of the Pfizer vaccine stimulated “very strong” antibody responses, according to the study, as well as “very strong T cell responses,” referring to another arm of the immune system.
It is not known how long the post-vaccination immune response will last in people who have already been infected compared to those who have not.
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