Will we need a third dose of Covid-19 vaccine?

Likely, which is why studies in the field are progressing. But a lot will depend on the evolution of the virus and the pandemic, as well as on the duration of the immune response

(photo: Spencer Davis on Unsplash) One, two, maybe three. And so on, every year. The question of doses has been more central than ever when it comes to anti-Covid vaccines. Always. Leaving aside the technical issues - you will remember the possibility of extracting multiple doses from vaccine vials - the number of doses was central in the discussions of vaccination strategy and efficacy. Starting from the United Kingdom, with the choice of mass vaccinating the highest number of people with a single dose initially, up to the evidence regarding efficacy against variants (and it seems, for example, a double dose makes the difference against delta variant (B.1.617.2, a strain of the variant sequenced in India).

Thus, while now the campaign is in full swing with us too, with the latest openings, regardless of age range or categories, for some time we have begun to look to the near future. Basically we are already talking about a possible third dose (except for Johnson & Johnson, the only one at the moment to foresee one instead of two), to mean more generally a vaccine booster Will it be needed every year? The answer is very vague, but the practically shared idea is that it is possible and that we must prepare.

Big Pharma knows this well, and for some time. Only in January, in fact, shortly after the approval of its vaccine, Moderna for example announced that it was at work with an experiment to understand if a third dose of its product, a booster, could increase its effectiveness, especially in the fight against ' emergence of new variants. The variants node in fact, together with the question or on the duration of immunity conferred by natural infection and vaccine, are the central themes in the discussions on the usefulness or otherwise of a booster, with identical or updated versions of the vaccine, or aimed at fighting in more specifically the variants. A vaccine that uses the genetic information of the variants for the production of the spike protein against which to direct the immune response, easily and rapidly adaptable, especially with the technology of mRna products. This is what the Moderna company did, launching an experimentation with a specific vaccine for the beta variant B.1.351 (discovered in South Africa), which according to the results released only a few weeks ago manages to enhance the immune response against the variants.

The other great enigma faced with the need for one (or more) possible boosters, has to do with the duration of immunity acquired after vaccination (and more generally after exposure coronavirus). The studies accumulated so far have produced somewhat different data, but lead to believe that the immunity acquired after the infection, albeit with some variable from person to person, decreases over time but generally lasts at least a few months, about six. even with vaccines, perhaps years, although it is not entirely clear what level of immune response is necessary to ensure protection.

The publication of a recent study on the subject, which observed the presence of cells that produce antibodies almost a year after recovery, he argues in favor of the existence of a very long-lasting immunity, due to the presence of long-lived cells, capable of producing antibodies against the coronavirus potentially for life. But whether this is sufficient to provide protection, again, is not clear.

And that is why we need studies, and data. It is in this direction that the UK initiative also goes, which has just launched a study to understand if and to what extent a third dose of the anti-Covid vaccine (other than those tested) helps to boost the immune response. Combining several, considering that the booster, the third dose may be different from those previously received. However, attempts to combine it with other vaccines are also underway. Pfizer, for example, has just announced plans to administer the third dose of its Covid vaccine alongside pneumococcal vaccine in adults over 65.

Preparations are essentially already in place, as required , as commented, among others also the American expert Anthony Fauci questioned on the subject. It would be "foolish" not to, he said, even considering the climate of uncertainty in which we find ourselves. In fact, faced with the uncertainty about the duration of immune responses to natural infection and the vaccine, there are also those concerning the epidemiological evolution of the pandemic, with the spread of variants and their ability to evade vaccines or not.

With several now approved, and even with studies still in progress, there are those who are unbalanced to imagine the type of booster we could receive. For example, Nathan Bartlett, expert on respiratory infections of the Newcastel Universiy, on the pages of The Conversation, explained how hardly in the long term, if required, the solution will be to resort to adenovirus vaccines (such as Astrazeneca or even J &). Not only for the rare coagulation problems associated with vaccines, but because repeated cycles in fact with adenovirus products risk becoming less and less effective, because the immune system also responds to the adenovirus, interfering with the ability to release the genetic material necessary to assemble the response against coronavirus.


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