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After two years almost disappeared, the gripe It has circulated again this season, especially between February 28 and March 13, when a significant increase has been detected, coinciding with the drop in Covid cases, as reflected in the data from the Influenza Surveillance System in Spain.
The report for week 10/2022, which collects data from March 7 to 13, 2022, points out that all surveillance indicators indicate “an increase in the circulation of influenza viruses, both in surveillance of ARIs and ARIs, as well as in data from non-sentinel sources. This evolution should be confirmed in the coming weeks. Specifically, 14 positives have been reported in sentinel samples for ARIs (acute respiratory infection in Primary Care), 4 for ARI (severe acute respiratory infection in hospitals) and 509 arrests in non-sentinel samples.
A considerable increase if we take into account that the report for week 8 (from February 21 to 27, 2022) only reflected two cases of influenza in ARI sentinel samples, 0 in ARIs and 56 in non-sentinel samples. And figures well above what was seen in week 10 of last 2021, when no positives for influenza were detected in samples.
Catalonia and Castilla y León have already announced that they are at epidemic levels. But Dr. José María Eiros, director of the National Influenza Center in Valladolid, calls for calm in the face of a situation that he describes as “normal.” «We are still in flu season, which in the northern hemisphere runs from October 1 to March 31. What the sentinel networks of Catalonia and Castilla y León have detected is that we have exceeded a threshold that by convention we accept is the epidemic », he explains in conversation with ABC.
This season also, there has not been a single peak, but the behavior of the flu has been “biphasic”, as there was another small uptick in cases last December. Experience in pandemics has shown that other non-dominant respiratory viruses sometimes maintain activity outside of their conventional time, seeking their niche. The expert recalls that he was seen with RSV during the influenza A pandemic in 2009 and with the Covid pandemic in 2021, when there was a rebound in the virus that causes bronchiolitis, with cases above expectations, although without reaching an epidemic, in late spring.
The expert confirms that, from February to last week, they have noticed a increased activity of the influenza A (H3N2) virus, but in this case they do not expect it to go any further. “We believe that the height of the flu virus season will not last long,” says Dr. Eiros.
The expert assures that “serene analysis and reflection” will be needed later on the variables that may have conditioned the behavior of the flu this season. In any case, he considers that both the hygienic-sanitary measures (distance, masks, avoiding crowded interiors) and the increase in flu vaccination rates in the elderly and in health professionals are “factors that have undoubtedly contributed to minimizing the activity of respiratory viruses in general and of influenza in particular.
Two years later, we are still not reaching the worrying levels of flu that were seen every winter before the Covid pandemic. If we look at the report for week 10 of 2020, just before the lockdown began, 66 positives had been detected in sentinel samples and 92 in non-sentinel samples. But in the accumulated of the season, the difference is very wide. As of March 8, 2020, 2,486 positives had been detected in the sentinel network and 6,444 in non-sentinel samples since September 30, 2019. In this 2021-2022 season, from October 4 to March 13, we have 98 positives in sentinel samples (adding ARIs and ARIs) and 3,427 detections in non-sentinels.
“We have not returned to the flu figures from before the Covid pandemic. This season has been moderate and the previous one was mild”, concludes Dr. Eiros.
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