Home » Covid vaccines, what is the third dose for?

Covid vaccines, what is the third dose for?

by admin

The SARS-CoV2 pandemic has been underway for more than 20 months now. We have obtained several safe and effective vaccines in record time, however a question arises: what will happen?

It is impossible and incorrect to make long-term predictions. But to understand what will happen, at least in the short term, we can observe the countries where the pandemic is in a different phase from ours and try to emulate the winning choices. One case above all is that of Israel, which completed its vaccination in record time last spring, and which has given us hope that it has achieved much-needed herd immunity. However, the Israeli summer brought record infections, explaining that – for now – herd immunity remains only an idea.

Covid, in Israel it is the turn of the vaccine for children

by Sharon Nizza


What happened in Israel?

Israel has decided to vaccinate as many people as possible by the summer: by March it had reached about 50% of the vaccinable population. This effort paid off in the short term but was thwarted by the drop in antibodies. The antibody drop (in English: antibodies waning) is a natural phenomenon for which, after exposure to a pathogen (both naturally and through a vaccine), the number of neutralizing antibodies against that particular pathogen decreases over time.

Pfizer vaccine, a study from Israel confirms: the third dose is needed, protection decreases after three months


This breakdown of neutralizing antibodies allows for example a vaccinated person to contract the virus and infect. Fortunately, the collapse of antibodies does not mean total absence of protection, in fact even after 6 months the risk of death for a vaccinated subject is very low compared to a non-vaccinated one. The explanation lies in the fact that there are not only neutralizing antibodies to protect us from the disease, but also T lymphocytes, memory B cells, etc.

See also  AUSL | Communication and press

For the same reason, serological tests are useless in predicting individual protection with respect to Covid19.

Anti-Sars-CoV2 antibodies last an average of 6 months

Data from Israel and other parts of the world confirm that the protection of current vaccines against symptomatic disease is about 6 months: in the six months after the second dose of vaccine the probability of getting sick with Covid19 is very low, while after 6 months you run a higher risk.

Furthermore, many works report that subjects recovered from Covid19, but who received a double dose of the vaccine, have the highest antibody titer ever. This finding suggests that 3 independent exposures (virus + 2 vaccine doses) confer excellent protection from future infection.

The third dose

Israel managed the increase in summer cases by administering the third dose to the entire population, regardless of age and / or medical condition. Thanks to the third dose, along with other measures, Israel managed to contain the contagions of the fearsome Delta variant. From the preliminary reports come at least two good news:

1) the antibody titre developed after the third dose seems to be higher and longer lasting than the first two;

2) it seems that the rare side effects associated with mRNA vaccines are even rarer in the third dose.

Both news must be confirmed and corroborated by further data that will soon arrive from other countries.

Why does the third dose seem to be so effective?

At the moment there is no literature on the third dose in the context of Covid19 (for obvious reasons) but a possible explanation can be extrapolated from other diseases and the functioning of other vaccines. We know that the vaccine works by simply exposing our immune system to an antigen (a protein characteristic of a virus), so that we can train and organize against it. We know that our immune system optimizes and improves its response in case of multiple exposures: in practice it becomes more and more efficient in fighting a specific antigen (virus).

We can imagine the vaccine doses as a series of workouts for our immune system that specializes and strengthens to do better and better a precise exercise. Many other vaccines are given in multiple doses, such as the one for hepatitis B which has up to 3 doses.

TAKE HOME MESSAGES:

1) The pandemic has started for about a year and despite the enormous progress in understanding and managing the virus we have to accept that we do not know some things;

2) The immune response generally decreases with the passage of time, with increasing age and in the presence of certain medical conditions;

3) In general, our immune system is strengthened with multiple exposures to the same antigen;

4) The third dose is essential to reduce contagion and symptomatic disease.

(The images used are for illustrative purposes only and do not report official data)

REF:

https://www.nature.com/articles/s41590-017-0006-x

https://onlinelibrary.wiley.com/doi/full/10.1002/cti2.1319

https://www.medrxiv.org/content/10.1101/2021.09.16.21263576v1

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)02249-2/fulltext

https://www.nejm.org/doi/full/10.1056/NEJMoa2114255

https://www.theguardian.com/commentisfree/2021/sep/27/data-israel-covid-booster-shots-standard

.

You may also like

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

Privacy & Cookies Policy