The flu reappears in Spain after two years hidden by covid-19

A woman is vaccinated against the flu in Zaragoza. / EFE

Surveillance systems confirm an increase in the circulation of these viruses and find 4,168 cases of the disease compared to 12 last year

After two years with hardly any cases, the flu has reappeared this winter, and it has done so relatively late (at the end of March) taking advantage of the decrease in infections by covid-19. "All surveillance indicators indicate an increase in the circulation of influenza viruses," highlights the Carlos III Institute in its latest report, published this Thursday. The Influenza Surveillance System in Spain (SVGE) has detected 4,168 cases of influenza in eleven communities until March 20 and in contrast to 2021, when only 12 cases were registered until March 31, the figure seems high, but the experts point out that it is within the usual parameters. Of course, in some autonomies the rebound is greater, such as in Castilla y León, which has entered an epidemic situation (50.66 cases) upon reaching 64 per 100,000 inhabitants. Catalonia is also above 50 cases.

“Flu surveillance is carried out between October 1 and March 31, what is called the flu season, and although we are in the final part, the situation is normal. A flu pandemic is not coming, there is no need to worry, ”explains José María Eiros, director of the National Influenza Center of Valladolid. This doctor recalls that at the beginning of the campaign there was also a rebound and stresses that the protection measures used against covid-19 (especially masks, social distance and hand hygiene) also work against the flu.

The situation has changed in 2022, and this is how it is perceived in Primary Care, the first defense against any health emergency. There, in recent weeks, "the jump regarding the flu has been brutal," says Lorenzo Armenteros, spokesman for the Spanish Society of General and Family Physicians (SEMG), who explains that all respiratory pathologies (covid, flu and respiratory syncytial virus) have been found more, among other reasons, due to the improvement in detection systems after the pandemic. “Flu is a disease that affects young people above all, and specifically, those under 15 years of age, what happens is that the most serious cases occur in older people,” says Armenteros.

This year, the H3N2 subtype of influenza, influenza A, is circulating in Spain, but not the one from 2009, but one more similar to the one that caused a pandemic in 1968. And vaccination is the main defense against the disease, although this year , says Armenteros, the vaccine is being less effective than in previous seasons. “The circulating strain was not included in the vaccines. Influenza vaccines are made each year taking into account which strain has circulated in the southern hemisphere, but this time, a different one has been taken from the one that now punishes us », he points out.

"We had been almost flu-free for a few years because the entire viral space was taken over by SARS-CoV-2, but now that infections have dropped, the flu has a certain role again," says Joan Carles March, professor at the School Andalusian Public Health. The appearance of covid-19 had a notable impact on the flu, not only in Spain, but in Europe. In 2021, the European Center for Disease Prevention and Control (ECDC) confirmed the campaign with fewer cases and in Spain, the Carlos III certified flu activity at "very low" levels, "probably due to the impact that health measures implemented to reduce the transmission of SARS-CoV-2 have had on the transmission of influenza.