Vaccine adherence: a major key to returning to life before?

Vaccine adherence: a major key to returning to life before?
Vaccine adherence: a major key to returning to life before?

Paris, Thursday April 8, 2021 – We no longer talk about the world after, but we still seem to miss the world before. The one where we simply did not measure the price of simple freedoms: living without a mask, without worrying about the curfew and without wondering about the establishments that remain closed or not. In France, the public authorities are very cautious about this return to life before. Admittedly, the tone of the messages bets for a summer which could have the appearance of a pseudo-normality, but we know that the prospect of mid-May mentioned by the President of the Republic in his speech last week should not in be only a very limited taste.

An effective weapon but which requires tireless work

If the temporality is uncertain, the weapon of conquest is more consensus (at least among political leaders): vaccination. Even if scientists warn, such as epidemiologist Antoine Flahault on the fact that ” betting everything on vaccination is a (very) risky bet “, It is nevertheless put forward as the decisive element for a return to a life” normal “. The examples of countries where vaccination rates are three times higher than in France (Bahrain, Chile, United States) which are now experiencing a new increase in the number of infections confirm, however, that the road will be long.

No salvation without a massive vaccination… including even the youngest

Models carried out by the Institut Pasteur, which have just been published, attempt to assess the vaccination coverage that would be necessary to abandon all the barrier measures. Simon Cauchemez’s team first retained as a working basis a vaccine efficacy allowing a 90% reduction in serious forms and an 80% reduction in the risk of being infected. It then set itself the objective of a daily number of admissions to the hospital of less than 1000. Considering that the current R0 is 4, taking into account the largely majority circulation of the B.1.1.7 variant (known as British) of which the contagiousness is more important, the modelers of the Pasteur Institute estimate that with 90% of the over 65 years vaccinated and 70% of the 18-64 years, it would remain necessary to maintain measures allowing to reduce the rates of transmission of 15 at 27%. If these are not highly restrictive measures (in the models of the Institut Pasteur, confinement as strict as that of March 2020 allows an 80% reduction in transmissions), we can measure it, the return to life totally normal is strongly compromised. To claim this, it would take either a vaccination of 90% of adults, or a vaccination of minors (which today has not been implemented in any country in the world but could possibly begin in May in Israel with the Pfizer vaccine. BioNTech). If children could also be vaccinated, a vaccination of 60% to 70% of those under 65 and 90% of those over 65 could make it possible to consider the end of all measures.

Multiple uncertainties

Like any modeling (and the last few months have brought many examples!), The latter must obviously be the subject of multiple reservations. Simon Cauchemez himself recognizes: “ You should not be in the position of a staunch believer or a complete skeptic, but find some kind of happy medium. I would be happy if lower vaccine coverage levels were enough to get life back to normal », He notes. The limits of these modelings are in fact numerous.

Some of them are initially impossible to determine and relate in particular to the evolution of the virus, whether in terms of its mutations or its interactions with the environment. The fragility of the concept of collective immunity (obtained naturally or thanks to vaccination) vis-à-vis SARS-CoV-2 has in fact already been the subject of numerous warnings. Others concern the failure to take into account acquired immunity following infection. Still according to models from the Institut Pasteur, it now concerns 21% of the population. On the basis of these figures, epidemiologist Catherine Hill calculates for Marianne ”
Taking into account the fact that 21% of French people have already had the Covid, according to the Pasteur Institute, it is still necessary to vaccinate about 57% of the population … This corresponds to 38 million people, or 74% of the whole of the adult population. In theory, it is therefore possible to achieve collective immunity without vaccinating the youngest, but it takes nearly 80 million doses “. We can also observe that the fragility of these models is also linked to the fact that they are themselves based on hypotheses that have not been fully validated (such as the level of reduction in transmission thanks to the various measures or the proportion of people naturally immune or the R0 linked to the English variant etc). Finally, the hospital objective chosen by Simon Cauchemez’s team (less than 1,000 admissions per day) may not be that of public policies.

Coverage rates unattainable in the current state of membership levels

Taking into account these many unknowns which are added to the uncertainties on the vaccination rhythm, the delivery of the doses (overall and by type of vaccine since that of AstraZeneca can only concern those over 55 years old) and to the variations concerning the vaccination schedule. (depending on the vaccines and the serological status of the people), the estimates of the date from which one could theoretically achieve an adequate vaccination coverage are very complex to establish (without also mentioning the fact that the Pasteur Institute does not retain the assumption of protection from the first dose).

One thing is certain, however, these models remind us that the real challenge will be that of adherence to vaccination. This is what Simon Cauchemez once again notes in Le Parisien. ” One of the strong messages that these models make it possible to convey is that even if I am not at risk, it is useful that I get vaccinated so that we can return to a normal life. If we only vaccinated the most fragile people, that would not be enough “. However, more than the availability of doses or the organization of the campaign, this could quickly become the main challenge.

Indeed, the latest wave of the CoviPrev survey carried out by Public Health France reports that only 56% of people who have not yet been vaccinated say ” definitely or probably wanting to be vaccinated “. In addition, an IFOP survey carried out in early April, indicates that membership drops to less than 50% among those under 35. It is this battle that today seems to have to be fought urgently.

Aurélie Haroche

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