This graph shows how quickly a third dose of vaccine can improve immunity

Two injections is good, but when it comes to preventing symptomatic infections from Covid-19, three injections might be even more effective. It’s hard to say what the long-term benefits of the coronavirus booster shots will be, as no one has had this third dose for long enough in their body. But immunologists generally agree that boosters several months after the first vaccination give the immune system a boost.

Early studies of vaccine booster shots around the world are starting to suggest that the protection obtained when people receive an additional injection several months after their first vaccination is more potent, causing antibody levels to rise to high levels. new heights and strengthens (at least temporarily) protection against Covid-19.

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Consider the available data from Pfizer’s booster injection trial, which involved around 10,000 people who received two injections of the company’s vaccine. The trial participants were divided into two groups: approximately 5,000 received a third dose, while the remaining 5,000 received a dummy injection (placebo) containing no additional vaccine.

It didn’t take long to spot the difference between people vaccinated with and without the booster. As Pfizer has shown in the graph below, people who have received a third dose begin to experience increased protection against symptomatic coronavirus infections just days after their injection.

You can see in this graph how the booster shots start to take effect after just a few days, providing more robust protection against symptomatic Covid-19, at least for a few months. CDC ACIP, November 19, 2021. Pfizer

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“If you look at blue, that’s what happens after you get the third booster dose,” Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said Monday, Nov. 22. a White House briefing, explaining how to read the chart. He tracked the number of symptomatic coronavirus infections in Pfizer trial participants for 100 days after they were vaccinated.

Anthony Fauci pointed out that people who received boosters in the Pfizer trial (blue line) had a much lower incidence of Covid-19 than those who had only had two injections and received a placebo. (Red line).

“Unmistakably, the effect of the booster injection,” said Anthony Fauci.

Improved protection against symptomatic Covid-19 manifests in about a week or two

According to Pfizer, the relative vaccine efficacy of the booster dose here is 95%. This means that 95% of people in the Pfizer trial who fell ill from Covid-19 were vaccinated but did not receive a booster, while the other 5% of sick people received a booster. Scientists began counting symptomatic cases of Covid-19 from seven days after the boosters were injected, and continued to do so until day 100.

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But you don’t have to take Pfizer at your word.

A trial by the National Institutes of Health divided people who received Pfizer, Moderna, and Johnson & Johnson vaccines into different booster groups and showed that regardless of the combination of the initial vaccine and the booster, antibody levels increased. (suggesting better protection against infection), with improvements peaking about two weeks after the booster.

Another UK study (still under scientific review) found that booster shots given from September on for both Pfizer vaccines and AstraZeneca vaccines boosted efficacy. vaccine in people over 50 to over 93%, which is a dramatic improvement.

Data from Israel indicates that after 12 days, the rate of infection in people who received a booster injection is 11 times lower than in those who were vaccinated, and that the rate of severe illness is divided by more. 19 in people who received a booster injection.

In any case, a trend is emerging. The boosters boost our immune response, which reduces the risk of contracting Covid-19, at least for a while.

But vaccine experts also stress that it’s important to remember that the benefits of a booster shot will likely wear off over time. Reminders can be a good idea before people gather for the holidays, but they won’t last forever.

Dr William Moss, executive director of the International Vaccine Access Center at Johns Hopkins University, told Insider: “It’s a normal part of our immune system: after a vaccination or exposure, our antibody levels increase considerably, then they decrease over time. They must come down again, otherwise our blood would only fill up with antibodies. “

Fortunately, vaccination also promotes a longer lasting memory immune response that works several months longer compared to antibodies, which means that even if vaccinated people get sick, they are generally well protected against the worst effects of Covid-19.

Version originale : Hilary Brueck/Insider

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