Covid-19. Infinite variations and waves? We asked the experts

First wave, second wave, third wave… soon the eighth? Since March 2020, we have been facing a repetition of the epidemic waves of Covid-19. And just like the regular increases in the number of cases, the variants follow one another (Alpha Delta, Omicron…), as well as the sub-variants.

Even if the virus is better controlled thanks to natural immunity and the various vaccination campaigns, this succession of waves and variants seems endless. So will we face endless waves and new variants? Explanations.

A new wave every four to six months?

On French Culture, the professor and infectiologist at the Bordeaux University Hospital, Denis Malvy, drew a parallel, on August 19, 2022, between the recurrence of waves of Covid-19 and the end of the immunity produced by vaccines. “The SARS-Cov2 virus produces variants and sub-variants over a rhythm of six to four months. This appearance is linked to the fact that vaccination protects over a relatively short period of time,” he explained. In other words, past these four to six months after vaccination, the population would be less immunized and therefore more receptive to the transmission of the virus.

For Pascal Crépey, teacher-researcher in epidemiology and biostatistics at the School of Advanced Studies in Public Health in Rennes, successive epidemic outbreaks are not just linked to the loss of immunity but are also determined by the appearance of new variants. and by climatic conditions more or less favorable to transmission.

It is the combination of these three factors that triggers epidemic waves. “The Delta variant was at the origin of the fourth wave in the summer of 2021, but could also cause the fifth thanks to the winter”, he raises. And immunity acquired against one variant does not always have a decisive effect against another: “The Omicron variant arrived at the end of Delta’s winter surge, when the population was immune enough to halt Delta’s growth,” he explains. In short, epidemic waves remain complex phenomena in which all the variables are not under the control of specialists.

Read also: Covid-19. Eighth wave, new variant? Here are the four back-to-school scenarios

A virus that will become seasonal and not serious?

For how long will we have large waves? “The bottom line is whether there will be new, very different variants of Omicron,” answers Yves Buisson, epidemiologist and president of the Covid cell at the National Academy of Medicine. A scenario “who would reshuffle the cards”, but currently unlikely, virological surveillance not showing this trend. “If we continue like this, we will have ripples and probably end up arriving at an epidemic which will resemble that of the flu, with winter outbreaks”.

Pascal Crépey judges that the Covid-19 will be considered as a simple virus when it is no longer a public health problem, “that is to say when we will have the means to treat it effectively so that we no longer have serious forms: this requires effective treatments and routine vaccination”.

What about new vaccines at the start of the school year, which laboratories tout as more targeted and therefore more effective against the virus? “We were disappointed with the duration of protection conferred by vaccines against infection,” recognizes Pascal Crépey. “If new vaccines that combine different strains make it harder for the virus to find escape routes, the situation can only be better”.

Read also: Covid-19. Will the fourth dose of vaccine be open to everyone by the fall?

Unequal management of the pandemic at the global level?

Would the zero Covid policy adopted by some countries, particularly in Asia, delay the end of the epidemic at the global level? This is what epidemiologist Yves Buisson thinks.

“In China, the population does not develop hybrid immunity because the authorities do not let people become infected so there is no natural immunity”, he lets go. “These are populations that are very poorly immunized and in which the virus can regain the hair of the beast and relaunch the epidemic around the world”, he continues, castigating the lack of homogeneity in the fight against the Covid at the global level. “The entire world population must acquire collective immunity to regulate the circulation of the virus”.

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