After the explosion of RSV bronchiolitis cases in autumn and a first epidemic wave of influenza A in November and December, now it is the turn of subtype B, which affects more people under 15 years of age.
The stabilization of SARS-CoV-2, as one more among the circulating respiratory viruses, it has marked the changes of this season. First it was a outbreak of respiratory syncytial virus caseshe, later arrived the flu, mostly A and much sooner than expectedand now the season is extended by the hand of the B strain of influenza.
And again, as at the beginning of the viral season, this pathogen focuses on the smallest. The latest report from the Carlos III Institute, the Sivira, points this out. The rate of influenza in primary care describes a second seasonal wave of influenza associated with the circulation of influenza B viruses. The highest rates of influenza are observed in those under 15 years of age.
The cases of respiratory infections, according to the aforementioned report, have grown in the last four weeks, after a decrease in cases that occurred at the end of January. Then ended the first wave of influenza mainly carried out by strain A and now, since the beginning of February, a continued rise in the B strain has been observed.
The evolution of the flu this season had a first wave with the peak of maximum activity (249.6 cases/100,000 h) in mid-December descending at the beginning of January. After that, throughout the following month a progressive increase in infections has been observed. At the end of February, the flu rate in primary schools was in 258.5 cases per 100,000 ha figure greater than that of the previous epidemic wave.
Since the start of the season 18,907 samples of acute respiratory infections have been analyzed for the diagnosis of influenza. In them, 4,055 detections of influenza viruses have been identified, 2,947 type A (73.4%), of which 1,948 are A(H3) and 597 are A(H1)pdm09, (76.5% and 23.5%, between subtypes) and 402 A not subtyped (10%). In addition, 1,068 (26.6%) of type B were identified. Outside the health circuit, many cases have been diagnosed thanks to home tests, available since last autumn, to differentiate between Covid, influenza A and B.
This year’s flu vaccines contained the subtypes found, two strains of A and one (or two in the case of quadrivalents) of B. According to data from the Gripmetro (a tool that monitors coverage by Sanofi communities) the national average of those over 65 years of age vaccinated against influenza is 67.3%between 60 and 64 it remains at 37.5%, it barely exceeds 10% (11.7%) between 64 and 18 only 8%.
Until now, influenza B was unknown and underappreciated. The two circulating lineages of this subtype, called Victoria and Yamagata, were more common before the 1980s, and have circulated ever since, but giving way to the A subtypes. VIII CSL Seqirus Update on Influenza held in Toledo, various experts such as Ana Fernandez-SesmaProfessor of Microbiology at the Icahn School of Medicine at Mount Sinai in New York, and Joan Puig Barber, from the vaccine research area of FISABIO, pointed out the possibility of the disappearance of Yamagata.
What is the influenza B virus like?
Jordi Reina, from the Virology Unit of the Microbiology Service of the Son Espases University Hospital, in Palma de Mallorca, describes in a recent article the characteristics of this subtype. “Globally, influenza B occurs biannually, almost always after the epidemic wave of influenza A, and represents about 25-30% of all reported influenza cases globally, although its percentage varies according to the epidemics and the geographical areas considered”.
However, Reina points out that “the clinical manifestations of influenza B are generally indistinguishable from those caused by influenza A“. Only a serology can tell what kind of flu it is. On the other hand, he alludes to his discovery. “In 1940 there was an outbreak of an acute respiratory disease in the child population which was clinically similar to influenza. From these patients it was possible to isolate a new virus that was serologically different from the already known influenza A virus; The new virus was named influenza B virus.
One of the advantages of influenza B is that “it is that the human being is its only natural reservoir and therefore there is the possibility that it can be eliminated through intensive and effective universal vaccination programs”, explains the virologist.
Less cases of VRS and Covid
On the other hand, VRS and Covid do not accumulate new ones. On the one hand, the rate of Covid-19 detected in outpatient centers has decreased slightly since the previous week, and the cases detected are observed in the 45-64 year-old group. Variants of SARS-CoV-2 currently circulating in greater proportion are, BQ.1.1 (57%), followed by BA.5 (23%).
He RSV no longer massively infects children. Now there are barely 9.4 cases per 100,000, when the peak in November reached 135.3 cases per 100,000 inhabitants.
According to the criteria of
Know more