The increasing prevalence of new variants of the coronavirus raises more and more questions about the level of protection even after vaccination: won't these changes in the SARS-CoV-2 virus escape the immunity obtained?

Vaccinated against Covid-19, will it be necessary to be re-vaccinated?

The increasing prevalence of new variants of the coronavirus raises more and more questions about the level of protection even after vaccination: won't these changes in the SARS-CoV-2 virus escape the immunity obtained? the microbiologist and infectious disease specialist William Petri, from the University of Virginia, answers in 6 points to the most frequent questions about vaccines and their recall.

1. What is a vaccine booster?

A vaccine booster is the injection of an additional dose, intended to maintain immune protection against a given pathogen. The process is common, because our immunity can weaken over time in a completely natural way. For example, the vaccine against influenza must be redone every year, those against diphtheria and tetanus every ten years.

Flu virus particles

Some viruses (here the flu) evolving very quickly require vaccines updated every year. Centers for Disease Control / CDC Influenza Laboratory, CC BY

The vaccine injected during the booster is often identical to the first. But not necessarily: when the targeted virus is known to evolve rapidly, its vaccine must be modified regularly in order to adapt to it: this is for example the case for seasonal flu, whose vaccine must be readjusted every year on pain of obsolescence.

2. Do we already need a reminder for the Covid?

At the beginning of July in the United States, after an intense vaccination campaign lasting several months, no health authority (Centers for Disease Control and Prevention, the Food and Drug Administration and the Advisory Committee on Immunization Practices) yet sees the interest. (Editor's note: in Israel, the authorities are encouraging people over 60 to take a third dose. In France, discussions are underway regarding the most vulnerable groups who were the first to be vaccinated.)

3. Why are recalls not yet recommended?

Even if the benefit of a vaccine is not eternal, the moment when it will fade in the case of Covid-19 is not yet established.

This in particular because all currently authorized vaccines against Covid-19 induce good immunity. They allow "memory" B lymphocytes of our immune system to register the properties of the pathogens with which we are confronted, and therefore to initiate the production of adequate antibodies in the event of further exposure. High level of memory B lymphocytes have in fact been detected in vaccinated persons (Pfizer) at least 12 weeks after injection.

Other studies also suggest that these vaccines, although they do not necessarily prevent contamination, offer some protection including against emerging strains of coronavirus. For Johnson & Johnson, 73% and 82% efficiencyagainst severe forms of the Beta variant were observed 14 and 28 days after injection, respectively. For Pfizer, preliminary results suggest a 88% efficiencyagainst the Delta variant.

Long-term immunity is also ensured by plasmoblasts. These cells, other actors in the production of antibodies, do not need a booster and were detected eleven months after injection in vaccinated people : which suggests the establishment of an effective immune memory.

A B lymphocyte, a major player in antibody production
Several cells of our immune system participate in the production of antibodies (here, B lymphocyte) and their memorization in the event of a new encounter. NIAID


4. How do I know if a recall will become necessary?

One sign of the need for a booster would be the growing epidemic among those vaccinated. For now, vaccines remain largely effective ... But the exact level of individual immunity they provide is still being evaluated.

To assess this immunity, researchers are looking in particular at certain antibodies induced by vaccines: those which recognize the spike protein, allowing the coronavirus to enter cells, and which would be of major importance.

In support of this idea, a study showing that mRNA vaccines (Pfizer and Moderna), which appear to be the most effective, generate a higher high level of antibodies in the blood than adenovirus vaccines (Johnson & Johnson and AstraZeneca). A preliminary study also suggests that the level of anti-Spike antibodies would be lower in former Covid-19 patients, including after injection of the AstraZeneca vaccine.

Of course, medical staff would like to be able to already offer their patients blood tests capable of reliably measuring their level of protection against Covid-19 ... Which would indicate, clearly, if anyone needs a reminder .

But until researchers know for sure how to measure immunity induced by vaccination, the sign to follow as to the need for a booster will be, as noted previously, the evolution of the number of infections in people who have been vaccinated ... especially after a certain age: in fact, after 80 years of age, vaccination leads to less antibody production and therefore an immunity that could possibly decline more rapidly than in the general population. The elderly could also be more sensitive to new variants.

5. Does being immunocompromised increase the need for a booster?

Immunosuppression could indeed necessitate a booster. One study showed that in 39 out of 40 kidney transplant recipients and a third of the dialysis patients considered, vaccination was not did not result in detectable antibody production. Same observation in another study, this time conducted in 20 patients with musculoskeletal diseases and under immunosuppressive therapy. In both cases, however, all patients were fully vaccinated.

This is not to say that vaccination is of no benefit to people who are immunocompromised. At least one study shows that a booster can have a positive effect: in a third of transplant patients vaccinated with Pfizer or Moderna, if the first two doses failed to detect antibodies, an immune response appeared with the third. (Editor's note: In France, The Directorate General of Health already recommend this third dose in some cases.)


MRNA vaccine vial
In immunocompromised people, a third dose of mRNA vaccines (Pfizer and Moderna) generated sufficient protection against Covid. CROCOTHERY / Shutterstock


How do we know, then, if we are immunocompromised and vaccinated, if our immune system needs this additional stimulation? Preliminary results suggest that a test specifically targeting anti-Spike antibodies induced by a vaccine could help to ascertain if the latter worked. But for the time being, in the United States, this kind of protocol is not yet recommended by the FDA.

6. Do I need the same vaccine for the booster as for the first injections?

It is very unlikely. It has been shown that mRNA vaccines (like those from Pfizer and Moderna) can even be paired with adenovirus vaccines (like AstraZeneca) without loss of efficiency.

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

Image Credit: BaLL LunLa /

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