What do we know about the effectiveness of vaccines against Sars-Cov-2 variants

What do we know about the effectiveness of vaccines against Sars-Cov-2 variants

A point on the scientific evidence collected so far, among the most widespread variants and the four vaccine formulations currently in use in our country. In any case, all vaccines are essential to prevent, in addition to the severe forms of Covid-19, the spread of further variants

(photo: Brano / Unsplash) As the months of the pandemic go by, they are also increasing, as was easily predictable, both the Covid-19 vaccines available and the variants of the Sars-Cov-2 coronavirus in circulation. Within this growing complexity, with a rapidly growing number of vaccine-variant combinations, it is easy to get lost: so let's try to put in order what we know today, even though we are aware that the scientific literature on the subject is updated almost every day. therefore they are necessarily not definitive truths, gathered to the best of what the scientific community has been able to establish up to now.

The variants of the initial form of Sars-Cov-2 are innumerable, but in terms of diffusion , of relevance and effective impact on health systems, the most relevant are currently reduced to four. Go to the headlines with the name of the country where they first reached a significant proliferation, are the South African (or, more scientifically, B.1.351), the Brazilian (B.1.1.28), the English (B.1.1 .7) and finally, last only in chronological order, the so-called Indian variant (B.1.617.2). Not to mention that the mutations of the virus are further intertwined, and that others emerge almost daily to keep an eye on (such as the Vietnamese one, to cite a recent case).

Another element of complexity, beyond the specific vaccine and the particular variant, is that in general there is a difference between having received one or two doses of the vaccine, and for some formulations we are already working on administering an additional booster dose to stimulate a specific immune response against certain variants. But let's go in order.

Indian variant (B.1.617.2)

As it is more recently identified, it is the variant of which we have the least consolidated knowledge, although we already know well about its high transmissibility. A very recent study published last May 22 by Public Health England estimated that the Pfizer-Biontech vaccine reaches an efficacy of 88% against the Indian variant two weeks after the second administration. Exceeding the estimates obtained by the company itself, which had estimated the effectiveness at around 75%.

With the double dose of the vaccine by Oxford-AstraZeneca, however, the effectiveness was estimated at around 60%. If, on the other hand, we stop at the first dose only, both Pfizer and AstraZeneca have been assessed a rather lower efficacy, equal to 33%.

Regarding the formulation developed by Moderna, it is known that the response to the variant Indian is a bit weaker than the other variants (for which it is very good), but we do not yet have quantitative data available. From the preliminary information available, however, the protective capacity of the vaccine should remain good. At the moment we have no published studies available even for the Janssen (Johnson & Johnson) vaccine, for which it is currently difficult to make estimates or predictions.

English variant (B.1.1.7)

According to a study published in the New England Journal of Medicine, Pfizer's vaccine is effective in preventing 87% to 89% of the English variant infection. And a research published in the Lancet has estimated an even greater effectiveness, even higher than 95%, while with the first dose alone (three weeks after the injection) it was around 50%.

Dai real-world evidence data, as reported by the BBC, the AstraZeneca vaccine would have a rather high efficacy, equal to 66% with the double dose and 50% three weeks after the first dose. With the same method, the efficacy of the Pfizer formulation with the double dose was evaluated at 93%. As for Moderna, from the first studies it seems that the antibody response is in general protective also against the English variant. , hopefully as much as Pfizer, but there are currently no quantitative estimates believed to be reliable. And finally Johnson & Johnson, for which (even without specific studies) the efficacy is between 72% and 57%, more likely close to 65%.

South African variant (B. 1,351)

According to Pfizer, the protection guaranteed by its vaccine against the Brazilian variant is close to three out of four cases, and in particular two weeks after the second dose the range is estimated between 72% and 75%. A study published in early April instead showed 100% effectiveness in preventing the symptomatic form of Covid-19, despite being conducted on a limited number of people (800 in all). And other specific studies are underway.

The news relating to Vaxzevria by AstraZeneca, for which there is also talk of a 75% efficacy in preventing severe forms, is not as great - but still very good. , while of a much lower value in preventing asymptomatic or mild forms of the disease, even close to 10%.

For Moderna there is already the reasonable certainty of a certain efficacy, even if there are no estimates precise and it is believed that the values ​​may be lower than the other variants. And also for Johnson & Johnson the effectiveness should be a little reduced compared to the other variants, but with still high values: from a study conducted in South Africa an efficacy of 82% was obtained against the most serious forms of the disease, and by 64% against moderate Covid-19.

Brazilian variant (B.1.1.28)

AstraZeneca seems - at least according to the few studies available - to lose much of its protective capacity against the South African variant, thus ensuring lower coverage than the other variants. On the other hand, the response guaranteed by the Johnson & Johnson vaccine seems to be good, with 68% against the milder forms of the disease and 88% for Covid-19 in severe form.

Regarding Pfizer's formulation and that of Modern, finally, the evidence is still preliminary: a laboratory study estimated a good immune response, even if lower than that of the other variants, while another similar research evaluated a comparable efficacy compared to the English variant. In short, it is a bit early to give certainties.

Other variants and other vaccines, but a single goal

As anticipated, the vaccine-variant combinations described so far do not exhaust the list at all of possibilities. Both for the emergence of new variants (here are those monitored by the World Health Organization) and for the many vaccines at an advanced stage of testing, the scientific evidence to be collected is innumerable. To cite just one of the many examples, the British Medical Journal has already reported that the Novavax formulation appears to be effective against the English variant, but much less so against the South African one.

There are, however, some general issues to keep in mind. bill. First of all, many manufacturers are already developing second generation vaccines specifically designed to be more effective against the variants known so far. Again as an example, we can cite the European mRna vaccine CureVac, for which - without the first version having yet arrived on the market - there are already in pre-print studies on animal models relating to the efficacy of the second formulation of facing the variants.

Secondly, for those who have already been vaccinated, the possibility of extending the vaccination cycle with an additional dose (the third or the second, depending on the type of formulation) is being contemplated: just in June a research called Cov-Boost starts with which 3 thousand people already vaccinated in December 2020 or January 2021 will be enrolled to verify how much the additional dose can be protective.

And then, of course, it is not worth getting lost too much in numerical differences. Although important to know and study at a scientific level, these distinctions of a few percent confirm that the priority is in any case to vaccinate as many people as possible and as quickly as possible, both because all vaccines guarantee good protection against severe forms of Covid-19 for all. (or almost all) the variants, both because reducing the general circulation of the new coronavirus allows to decrease the probability of new mutations. And, to quote Prime Minister Mario Draghi last weekend, "As long as the pandemic rages on, the virus can undergo dangerous mutations that can undermine even the most successful vaccination campaign".

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