This is a warning that Simon Cauchemez, head of the modeling teams at the Institut Pasteur, has chosen to highlight his new epidemic scenarios, in order to avoid any misunderstanding:
“The spread of the Sars-CoV-2 virus is difficult to anticipate and
the dynamics of the epidemic
can change rapidly.
The trajectories described depend on the assumptions made;
if the hypotheses do not come true, the observed dynamics may be different from the projections. "
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The latest works released on Monday are no exception to this rule.
To begin with, they do not take into account the emergence of the Omicron variant, none of whose exact properties are yet known, whether in terms of transmissibility, severity, vaccine escape and immunity.
“
Models allow us to explore a field of possibilities,
” recalls the researcher.
“
But if this field is too wide, what does it bring us?
We can imagine that if the variant escapes vaccines completely, the situation would be very bad, no need for a model for that.
It is the Delta variant that should be of concern to us for the moment
. ”
there is no fatality
What do the new calculations of his team tell us?
The idea is to take into account the progressive loss of efficacy of the vaccine on the infection and on the risk of hospitalization and to assess the benefit of extending the booster vaccine.
It shows that at the "current" rate of progression of the virus (estimated between November 2 and 20), we would have a risk of exceeding quite widely the peak of the second wave in February, by reaching 4000 daily hospitalizations (against less than 3000 the previous winter).
This is about twice as high as what was envisaged at the start of October.
But this is not inevitable, far from it. Assuming that the third dose increases the protection against infection above 80% and the protection against a severe form to 95%; that we will manage to maintain a rate of 400,000 daily injections in December; that this reminder is extended to over 18s five months after the second dose and that adherence is massive (80% of over 50s and 50% of 18-49 years); then the modelers estimate that we will be able to reduce the peak by approximately two. The researchers show in particular that the reduction of the delay from 6 to 5 months and the extension to young adults provides a significant benefit on the epidemiological level.
"The more we reduce the circulation of the virus, the more we limit the risk of seeing the most vulnerable go to the hospital"
because vaccine protection is not 100%, comments Simon Cauchemez.
These calculations are part of the elements that pushed the executive to generalize the vaccine booster policy.
The models also remind us that behavior change, that is to say greater vigilance brought to barrier gestures, remains an essential weapon against the epidemic.
Thus a reduction of only 10% of the reproduction factor of the virus, the famous parameter R, makes it possible to obtain the same result!
"This is an important message to get across: beyond the specific scenarios of loss of vaccine efficacy, it is the way in which we can react collectively by increasing our level of vigilance"
, supports the researcher.
Ventilation of rooms, wearing a mask, teleworking, social distancing: the formula is already well known.
With an R reduced by 20%, we might even have a relatively calm winter again.
“The arrival of the Omicron variant is certainly worrying, but all these vigilance measures should also be effective against it.
There is no reason to deprive yourself of it. ”
