The increasing prevalence of new forms of the corona virus raises a number of questions about the level of protection even after vaccination – will the changing forms of the SARS-CoV-2 virus break the protection provided by the vaccine? William Petrie, microbiologist and infectious disease specialist at the University of Virginia, answers the most frequently asked questions about vaccines and explains them in 6 points.
1. What is a vaccine booster?
A vaccine booster is an additional dose vaccine intended to maintain immune protection against a virus. This process is normal because our immunity can weaken quite naturally over time. For example, the flu shot should be repeated every year and the diphtheria and tetanus vaccines every ten years.
The vaccine given during a booster is often the same as the first one. But this is not necessarily the case: when the target virus begins to evolve rapidly, its vaccine must be regularly modified to adapt.
2. Do we need a reminder for COVID now?
In the United States, at the beginning of July, after several months of an intense vaccination campaign, no health authority (the Centers for Disease Control and Prevention, the Food and Drug Administration and the Advisory Committee on Immunization Procedures) seems to want.
3. Why is the revaccine not yet recommended?
While the benefits of a vaccine do not last forever, when the vaccine’s effect will wear off in COVID-19 has not yet been established.
This is partly because all currently authorized vaccines against COVID-19 produce good immunity.
Other studies also suggest that these vaccines, while not necessarily preventing infection, offer some protection against them, including protection against emerging forms of the coronavirus. For Johnson & Johnson, an efficacy of 73% and 82% against severe forms of the beta version was observed 14 and 28 days after injection, respectively. For Pfizer, preliminary results show an efficacy of 88% against the delta variant.
4. How do I know if a revaccination is necessary?
An indication of the need for boosters would be a growing epidemic among those who are vaccinated. So far, the vaccines are largely effective … but the exact level of individual immunity against them is still being assessed.
To assess this immunity, the researchers are paying particular attention to certain vaccine-induced antibodies, those that recognize the advanced proteins that allow the coronavirus to enter cells, and which will be of primary importance.
In support of this idea, a study shows that mRNA vaccines (Pfizer and Moderna), which appear to be the most effective, generate higher levels of antibodies in the blood than adenovirus vaccines (Johnson & Johnson et al. AstraZeneca). A preliminary study also suggests that after the AstraZeneca vaccine is injected, pre-Covid-19 patients will have lower levels of anti-peak antibodies.
Of course, medical staff would already like to continue performing blood tests of their patients who can reliably measure their level of protection against COVID-19. This will reveal the need for revaccination.
5. Does having low immunity increase the need for a booster?
Those with low immunity may really need a booster. One study showed that 39 of 40 kidney transplant patients and a third of dialysis patients did not produce detectable antibody production after vaccination.
This does not mean that vaccination does not benefit people who are immune. At least one study suggests that a booster may have a positive effect: a third of transplant patients vaccinated with Pfizer or Moderna if the first two doses did not detect antibodies, followed by an immune response in the third appeared .
6. Do I need the same vaccine as the first injection for a booster?
It is not very likely. It has also been shown that mRNA vaccines (such as those from Pfizer and Moderna) can also be combined with adenovirus vaccines (such as AstraZeneca) without loss of efficacy.
(The Conversation, William Petrie, Professor of Medicine, University of Virginia at Richmond)