Spoken last week, his words retain a strong resonance: “We should not forget that we are still in a pandemic. Nevertheless (…) we will quickly move towards a scenario closer to endemicity.” In saying this, Marco Cavaleri, head of vaccine strategy at the European Medicines Agency (EMA), confirms the hypothesis that we could quickly enter a new health era. With the extremely rapid spread of the Omicron variant – less pathogenic than its Delta predecessor – some hope that Sars-CoV-2 will become endemic. What are we talking about exactly? “The endemic is distinguished by cases occurring on a regular basis, but not necessarily in large numbers. However, there is a notion of time that no longer exists”, defines for L’Express Jacques Izopet, head of the virology department of the Toulouse University Hospital. On the contrary, the epidemic is characterized by contaminations which appear at a given period – in a limited way in time. The pandemic is an epidemic on a global scale.
When a disease becomes endemic, its presence stabilizes within the population. The circulation of the virus becomes under control and is, in fact, easier to monitor. However, would endemic necessarily be good news, knowing that HIV or malaria are also endemic and cause many deaths each year? “On a purely theoretical level, we can believe that an endemic situation with a strong circulation of the disease causes more damage than an epidemic situation. There is never a respite and that is what happens with the malaria. If the immunity of the population is good enough, the disease therefore targets young children”, explains Yves Coppieters, epidemiologist at the Free University of Brussels. But the situation is different with the less virulent Omicron variant. “If a virus that is not bad is circulating at a high level, then we will experience greater immunity. But if its circulation is low, our immunity will be less stimulated. We have to find a balance”
On the list of endemic diseases, very quickly, the example of AIDS also comes to mind. In 2020, around 680,000 people died from the disease worldwide, according to the UN. If the progress made on the quality of treatment and prevention have made it possible to lower the mortality rate, HIV is still circulating massively in the world and particularly on the African continent. “In the case of the AIDS virus, it is special: a person who is infected does not eliminate it definitively. Moreover, we have not seen any attenuation of the pathogenic power of the virus since its appearance around 1930”, emphasizes Jacques Izopet. A situation very different from that of Sars-CoV-2 for which we could eventually move, according to the specialist, towards an attenuation of the pathogenic character. However, the most fragile people will continue to be exposed to the virus even if an immune barrier – obtained with the vaccination and the spread of Omicron – rises in a large part of the population.
“Possibilities of Seasonal Outbreaks”
Consequently, older or immunocompromised individuals will remain those most at risk of developing a severe form. “For them, and for the people who are responsible for them (family caregivers, health and EPHAD personnel for example), it would be appropriate to have vaccines that could be regularly adapted according to emerging variants, a little as we do for the flu”, underlines Antoine Flahault, epidemiologist and director of the Institute of Global Health at the University of Geneva. According to the specialist, the endemic state is not a very appropriate denomination for a respiratory virus like the coronavirus: “For that of the flu, for example, we speak rather of an ‘endemic-epidemic’ virus, that is to say say of an endemic persistence of the virus in the population, but with the possibility of seasonal epidemic waves. In other words, if Covid-19 becomes endemic, we are not immune to seeing an increase in contamination occurring each winter, forcing public authorities to take measures to protect the most vulnerable.
According to several projections, it is possible that we are turning to a scenario similar to that of the flu. “This virus does not pose a problem, except in people at risk, until the arrival of completely new variants as was the case in 1918-1919”, analyzes Jean-Daniel Lelièvre, immunologist and head of the infectious diseases at the Henri-Mondor hospital. According to him, the logic is as follows: the more the disease progresses, the less of a problem it will be. For the moment, the hypothesis of an endemic seems to be taking shape, although it is difficult to see clearly. “We should remain cautious, there will probably be other waves before the disease becomes endemic”, advanced infectious disease specialist Éric Caumes on January 19 in L’Express. Several elements must be observed: the duration of population immunity, but also the ability of a new, more pathogenic variant to supplant the Omicron strain. Currently, scientists are closely monitoring a sub-variant of Omicron which has already become the majority in Denmark and which could cause a further increase in contamination throughout Europe. For now, however, data is lacking on this new strain.
“A new variant that would escape the immunity conferred by vaccines and previous variants, for example, would call into question more optimistic scenarios based in particular on the acquisition by the world population of increasingly strong immunity against severe forms. of Covid, which is called cell-mediated immunity”, continues Antoine Flahault. Despite this equation with several unknowns, some governments want to take the plunge. Like the Spanish executive who plans to consider Covid-19 as an endemic disease, which would justify a relaxation of restrictions. “It’s true that the Omicron variant leads us towards this perspective, but we don’t know if this scenario will last,” comments Yves Coppieters cautiously. On the side of Jean-Daniel Lelièvre, the Covid-19 is heading towards an endemic stage. “It’s a reality,” he insists. One thing is certain according to him: “This virus will not disappear from the surface of the Earth. We will never return to the world before and the counters will never be reset.”