an infectiologist compares the contagiousness of the Delta variant with that of smallpox. A parallel difficult to justify.
- The respective ORs of the Delta variant and smallpox vary greatly according to the different sources
- The smallpox mortality rate is 30%, very much higher than that of Covid
Delta variant as contagious as smallpox? It is a stone in the pond that has just launched on FranceInfo then on France 5 the infectiologist Benjamin Davido of the Raymond Poincaré hospital in Garches (Hauts de Seine). According to him, we would face this variant with “an OR, the element that measures a patient’s ability to infect other individuals, between 6 and 7, a figure that we know for smallpox”. A scary word. Smallpox – or smallpox – is a viral disease which, until the 17th century, was responsible for thousands of deaths each year in Europe. It was eradicated only in 1980, in particular from massive vaccination campaigns implemented since the end of the 1950s.
But the comparison would be risky. If it comes at the right time to justify projects of measures supposed to encourage the population to vaccinate massively, it is disputed. “The two diseases having very different modes of transmission – even if the smallpox virus can be transmitted, like SARS-CoV-2 by the close respiratory route, Ed – it seems to me risky to make comparisons“, replied for FranceInfo another infectiologist, Professor Daniel Camus of the Institut Pasteur de Lille.
RO: a “rough indicator”?
In fact, the real question to know if we can compare the contagiousness of the two viruses would be to know if the famous OR, yet presented as one of the criteria justifying the implementation of health measures, is a reliable indicator. For the Professor and head of the virology department at the Caen University Hospital, Astrid Vabret, also quoted by the FranceInfo site, the answer is clear: the reproduction rate would be, according to her, “a rough indicator“.
Relying on the comparison of the OR of SARS-CoV-2 and that of smallpox to estimate the dangerousness and the ability of the Delta variant to spread would therefore not necessarily be very rigorous. Especially since the respective ORs of the two viruses are also the subject of debates which are based on a range that is sometimes quite wide according to the different studies. Thus the OR of the Delta variant will vary according to the sources from 5.9 (WHO figure of June 17) to 7.2 (Scientific Council of July 7, 2021). As for that of smallpox, it would squarely make the big difference between 1.5 and 20! The last scientific publication on this subject in the journal Nature placed it in 2001 between 3.5 and 6.
An excessive comparison
So who to believe? And above all, is it useful, citing a historically frightening disease – the mortality rate for smallpox reaches 30%! – to further raise concern about the effect that the Delta variant could have on the continuation of the current pandemic? If it is only a question of playing on fear to legitimize an increasingly strong pressure on the French population to achieve a higher percentage of vaccinated people, this may perhaps work on the most sensitive people and the more chilly. But by making a manifestly excessive comparison, if only because of the disproportionate mortality risk between smallpox and the Delta variant of the coronavirus, Professor Davido’s claims could also become one more argument for opponents. the most convinced – and they have nevertheless shown their ability to mobilize during the demonstrations of the last weekend – of the idea of a “compulsory” vaccination.
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