Those who have been feeling that this year’s flu is more aggressive than normal are not imagining it. In several countries in the northern hemisphere, the flu season has started earlier than expected and with above-average intensity, putting pressure on outpatient clinics and hospitals and affecting different age groups across the board, not just the elderly and frail.
According to analyses published by Nature, one of the keys to understanding what is going on is the evolution of the influenza A virus, specifically the H3N2 strain. This is not a completely new virus, but one of its genetic “offshoots” that had been on the back burner in recent years and is now circulating strongly again.
A new version of the virus
The point is exactly this: many people had developed immunity based on exposure to dominant strains in previous seasons, but this new version of the virus is sufficiently different that it is able to evade those defenses to some extent. The result is a population that, despite having encountered the flu several times in the past or having been vaccinated, finds itself less protected than one might think.
Also complicating the picture is the timing. The flu wave arrived earlier than in recent years, catching both health systems unprepared and many people who had put off vaccination or counted on residual immunity. When the virus starts circulating earlier, it finds more susceptible individuals and is able to spread more rapidly.
The various factors
Experts stress that no single factor is responsible. The increased intensity of influenza appears to be the result of a combination: genetic changes in the virus, reduced effective immunity in the population, and circulation that began earlier than usual. A mix that explains why symptoms appear more widespread and, in some cases, more severe.
Better understanding these mechanisms is not just an academic exercise. It serves to improve the prediction of future flu seasons and to make the composition of vaccines more targeted. Influenza, in short, keeps reminding us that it is never really the same as it was a year before, and underestimating it remains the surest way to get surprised.
