Two weeks earlier and with a new variant: the flu is already here

BarcelonaThe flu is here. Two weeks earlier than expected, and in line with the predictions of health authorities, it includes a new variant that is expected to be more contagious. The Catalan Infection Surveillance Information System (SIVIC) confirms its rise: with 81 infections per 100,000 inhabitants, flu cases are on the rise, although transmission remains low. Currently, it is the second most common respiratory pathogen (13% of cases), behind rhinovirus—which causes the common cold and accounts for 42% of current infections—but ahead of respiratory syncytial virus (RSV), which traditionally preceded the flu epidemic in children and now causes 3% of cases per 100,000 inhabitants. According to Sivic, during the week of November 17-23, the incidence of all acute respiratory infections (ARIs) was 609 cases per 100,000 inhabitants, equivalent to 49,424 infections. Of these, 5,988 cases were diagnosed as influenza, which typically places greater strain on the healthcare system than rhinovirus. Currently, half of these cases are due to the predominant influenza variant (A H1N1pdm09), while the other half are caused by the K variant (A H3N2). This variant is largely responsible for the increase in infections in Europe, and the European Centre for Disease Prevention and Control (ECDC) has reiterated the need to vaccinate vulnerable groups (those over 65, pregnant women, immunocompromised individuals, and those with chronic illnesses), without the need for a flu vaccination program compared to previous years.

"Getting vaccinated now is one of the most effective ways to protect yourself and those around you against serious illness this winter," says Edoardo Colzani, head of respiratory viruses at the ECDC, adding that it will help reduce "additional pressure on health systems."

Will vaccines protect us?

In Catalonia, flu vaccination rates have risen to 62% among people over 80 and 47% among those aged 70 to 79, while among children aged 6 months to 4 years, the rate is currently 34%. However, if the flu strain chosen for this year's vaccines is not the K variant—a phenomenon known as a mismatch—will vaccination still protect the vulnerable population? The answer is yes.

The K variant is not a new virus, and the flu vaccine is designed to train the immune system to recognize parts of the virus that do not change between variants. This means it will have less potential to prevent infection, but it will significantly reduce the risk of hospitalization and complications (pneumonia and respiratory failure), and therefore the risk of death, which is the vaccine's primary objective.

It's important to keep in mind that imbalances aren't so uncommon: different strains of the flu can circulate in a single year, but stimulating the immune system to respond more quickly and strongly against the virus isn't only achieved through antibodies (which are like police officers patrolling the bloodstream), but also through the body's own immune response to the virus.