“We will move more towards a dynamic close to that of the flu than towards an endemic dynamic”

“We will move more towards a dynamic close to that of the flu than towards an endemic dynamic in the definition of the term”, explained this Wednesday on franceinfo Pascal Crépey, teacher-researcher in epidemiology and bio-statistics at the School of Higher Public Health Studies, in Rennes, while the European Medicines Agency believes that we should arrive at a sort endemicity, that is, a disease with which we will learn to live.

franceinfo: Are we going to reach an endemic stage and what does this mean in concrete terms?

Pascal Crepey: This means that we no longer have these epidemic phases of exponential growth with this dynamic which means that the number of new cases is multiplying from week to week. That we continuously have a certain number of cases in the population with a reproduction number around 1 and not above as is the case today.

Is it really possible?

Everything is possible but I fear that this does not really apply to the coronavirus for the simple reason that we have a seasonal effect which mechanically varies this number of reproductions. The virus is transmitted less easily during the summer period than during the winter period. So, we will not have this phenomenon of stability with an R around 1 all year round, we will necessarily have a variation between the summer period and the autumn-winter period. I think that we will move more towards a dynamic close to that of the flu than towards an endemic dynamic in the proper definition of the term. We will speak of a seasonal wave. With Omicron, we reach such high levels of transmission that it is hard to imagine that a new variant could be more transmissible than this variant and therefore the only path of evolution that remains is the path of immune escape. This is what the flu does every year and it is what justifies the annual flu shots. There is an antigenic shift which means that our immune system no longer recognizes the virus that is circulating and each year we have to be vaccinated against the flu. So, one could imagine the same type of strategy for the coronavirus in the more or less near future.

When can we stop testing?

The tests have two purposes. They make it possible to follow the epidemic, to know where we are and how to react or not. There is also the objective of preventing chains of transmission. So it is really a tool for public health, for controlling the epidemic. So as long as we are in the epidemic phase and in this wave, tests are an active tool in the fight. When we are out of this phase, we can ease off the tests and approach the possible next phase in the fall or next winter with a new strategy.

The European Medicines Agency and the WHO believe that injecting repeated booster shots is not a sustainable strategy. What do you think ?

It is an adaptive strategy to the epidemiological situation of the moment. The third dose of vaccine was not recommended against Omicron but against Delta because it was very transmissible and severe. Studies showed that protection against infection diminished over time. So it was necessary, with this winter wave of Delta, to ensure that the population and in particular the people most at risk are as protected as possible to avoid an influx of hospitals. The population must adapt to the epidemiological context and there is no reason to believe that there is a need to vaccinate every three or four months. On the other hand, next winter, we could again ask ourselves the question.

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