Seventh, eighth and now ninth. If the wave count of the Covid-19 is painful to you, it is possible to simplify things and evoke the ” triple epidemic», First of the name. The current situation is unpublished» et « full of uncertainties“, Public Health France alert. The Covid-19, influenza and bronchiolitis viruses are circulating at the same time on the territory and are all on the rise, raising fears of a hospital embolism for the end of the year. Sunday epidemiologists, trained in the school of the pandemic, will have to update their knowledge: the curves so familiar with the Covid are no longer enough to understand the situation.
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Until now, respiratory viruses followed one another at an almost immutable rhythm, a dance of the seasons, a hum of virologists. “Traditionally, we have a first circulation of rhinoviruses [responsables des rhumes banals] which then gives way to RSV [responsable de la majorité des bronchiolites],which usually gives way to the flu“, testifies Sophie Vaux, epidemiologist at Public Health France. But this year, a newcomer, Sars-CoV-2, has completely upset the epidemic calendar. Bronchiolitis showed up a month and a half early, the flu, already in the epidemic phase in Brittany and Normandy, is coming to the table much earlier than usual, while the eternal Covid returns, unfazed, for its ninth season.
A phenomenon of viral competition
« Until now, from the moment Sars-CoV-2 was present, we no longer saw the other respiratory virusesnotes Vincent Enouf, Deputy Director of the National Reference Center for Respiratory Infection Viruses at the Institut Pasteur.But was it due to the fact that the virus was “cannibalizing” its competitors or rather to wearing a mask, washing hands and above all confinement? It is difficult to separate things.Science has already documented this phenomenon of viral competition: a Scottish study published in the journal Proceedings of the National Academy of Sciences just before the pandemic observed that the peaks of rhinovirus and influenza were never simultaneous, demonstrating a probable interference between these two viruses. But knowledge of the interactions between respiratory viruses remains in its infancy. So that no specialist would come forward to predict whether the current wave of Covid could curb the flu wave or vice versa. “We need to allow ourselves some time to find out what will become of the three epidemics and see if this notion of viral cannibalism is confirmed or not.“, declares cautiously Didier Che, deputy director infectious disease at Public Health France.
Science is reduced to hypotheses
What mechanisms could explain this viral competition – which for the moment is not observed? Science is reduced to hypotheses. The role of interferons is often highlighted. These antiviral proteins, produced by the immune system during an infection, can reduce the risk of infection by another virus in the days that follow. “If there is interference between viruses, it is indirect, through our immune system. Do not imagine that viruses come into contact with each other», Specifies Mircea Sofonea, epidemiologist at the University of Montpellier. More simply, epidemics can engulf each other because of our behavior. “If people go back to wearing masks to protect themselves from Covid, this will have effects on the flu curve. If people who have symptoms isolate themselves more than before, due to Covid reflexes, this will also have an impact on the dynamics of influenza this yearremarks Mircea Sofonea. An important piece of data to integrate into the political equation: each new measure taken to fight against Covid, such as wearing a mask, will have a positive impact on the other two epidemics and will reduce the hospital load by the same amount.
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While viruses can to some extent neutralize each other, the current situation raises the specter of simultaneous infections. “Co-infections, we see them every year, for example influenza-RSV. We have also already documented Covid-flu co-infections. With this unprecedented situation of triple virus circulation, are we going to have more? For the moment, we do not observe more than usual in our laboratory“, tempers Vincent Enouf. In a letter published in March in The Lancet, Scottish researchers observed that Covid-flu co-infections, although infrequent, double the risk of death compared to a simple Covid. At the heart of this winter of all perils, only one certainty: science will progress. “Our gaps are still very large in terms of the interaction between viruses. We will make considerable progress in immunology“, predicts epidemiologist Antoine Flahault.