That's it, the flu is making a comeback. Influenza viruses have even taken their ease since almost all metropolitan regions are now even in the epidemic phase, according to the latest report of Public Health France. As every year, vaccination is recommended for health professionals and even more so for people at risk of severe disease. These are mainly people aged 65 and over, people who are obese or suffer from certain diseases (chronic respiratory diseases, cardiovascular diseases, diabetes, etc.) and pregnant women. This year's vaccination campaign began on 17 October. With the epidemic already off to a good start, is it still time to get vaccinated? Is the vaccine effective? And why do you have to do it every year? Answers with two specialists.
Reasons for annual vaccination
Influenza viruses are constantly evolving, sometimes with the appearance of genetic mutations. "From the moment a virus infects a person, it will mutate as it multiplies in the body, in particular to evade the immune system," explains Vincent Enouf, deputy director of the National Reference Centre for Respiratory Infection Viruses.
This characteristic requires that the composition of the vaccine be adjusted annually to introduce the four most recent viral strains in circulation. So to get vaccinated every year.
Relatively short duration of immunization
Especially since the protection conferred by the vaccine only lasts about six months. "From the moment you get vaccinated, the immune system is ready. It will attack and eliminate the virus more quickly," explains the respiratory virus specialist. Is there still time to do it for this season? "Yes, if it hasn't been done yet, it's urgent to do it because the epidemic is already off to a good start," says Sylvie van der Werf, a professor at the Institut Pasteur in the Department of Virology.
The vaccination campaign is not over, it is possible to get vaccinated until January 31. Knowing that the epidemic has just started, that a fortnight is necessary for protection to be effective and that a flu epidemic generally lasts 6 to 12 weeks, the game is still worth the candle. "But the ideal is to get vaccinated as soon as the doses are available in pharmacies," insists Vincent Enouf.
How effective?
Is the vaccine effective this year? "It's a bit early to say, we're only at the beginning of the epidemic so we don't have a lot of virus to analyse yet," replies Sylvie van der Werf. To develop the vaccine, "there are two meetings every year at the World Health Organization (one for the northern hemisphere, the other for the southern hemisphere) where the strains that should be part of the composition of the future vaccine are decided," the specialist continues. A gamble that viruses sometimes manage to thwart, which explains the lower effectiveness of the vaccine in some years. "But even moderate efficacy protects against severe disease," says Vincent Enouf.
And the first data on the 2023-2024 vintage are rather reassuring. "The viruses that are circulating at the moment are mainly type A (H1N1), which is in line with the vaccine," says Vincent Enouf. Last year, the vaccine's efficacy was estimated at 44%. This means that a vaccinated person has halved their risk of severe disease, which is no small feat. "We consider that an efficacy of 50% is very good for a flu vaccine," says the deputy director of the National Reference Centre for Respiratory Infection Viruses. As is the case with the Covid-19 vaccine, the flu vaccine does not necessarily prevent you from catching the virus and having symptoms. Its goal is to stop the virus before the infection escalates.
Is repeating vaccines dangerous?
Some people fear the harmful consequences of a succession of Covid and flu vaccines. After all, isn't it said that "it's the dose that makes the poison"? "Our immune system is constantly stimulated by everything we encounter, vaccines are just another encounter. To date, there have been no reported or documented negative effects of these repeated vaccinations," replies Sylvie van der Werf. "It is infection that can lead to the worst consequences, not vaccination. There is a sure way to protect yourself from it, people at risk would be really wrong to deprive themselves of it."