After the explosion of RSV bronchiolitis cases in autumn and the first influenza A epidemic in November and December, it is now subtype B, which affects most children under 15 years of age.
The stability of SARS-CoV-2, as one of the more circulating respiratory viruses, has been marked by changes during this period. First there was an explosion of cases of respiratory syncytial virus, then came the flu, mostly A and much faster than expected, and now the season is being extended by the strain of the rivers.
And again, as at the beginning of the viral season, this places the pathogen in the smallest. This is the latest report from the Carlos III Sivira Institute. The rate of influenza in primary care describes the second wave of influenza associated with the circulation of the influenza B virus, the highest incidences of which have been observed in children under 15 years of age.
Cases of respiratory infections, according to the report, have increased in the last four weeks, after a decrease in cases that occurred at the end of January. Then, the first wave of influence, carried out mainly by the A song, ended, and now, since the beginning of February, a continued rise of the B song has been observed.
The evolution of the rivers of this season had the first wave with the highest activity (249.6 cases / 100,000 h) in the middle of December, descending at the beginning of January. Then, over the next month, a progressive increase in infections was observed. At the end of February, the rate of infection in primary schools stood at 258.5 cases per 100,000 inh, a higher figure than the previous wave of the epidemic.
Since the beginning of the period, 18,907 cases of acute respiratory infections have been resolved for the diagnosis of influenza. Among them, 4,055 influenza virus detections were 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%) type B were identified. Outside the health sector, many cases have been diagnosed thanks to at-home tests, since the last case available, which differentiate between Covid, influenza A and B.
The vaccine stream this year contained the subtypes found, two strains of A and one (or two in tetravalent strains) of B. According to data from Gripometer (a tool that monitors coverage by Sanofi Communities) the average of those over 65 years of age vaccinated against the disease is 67.3%, between 60 and 64 remains at 37.5%, barely 10% exceeds (11.7%) between 64 and 18 only 8%.
Until now, influenza B was unknown and less well known. Two lines of this subtype, called Victoria and Yamagata, were more common before the 1980s, since then they developed, but subtype A. In the 8th CSL Seqirus Conference on Flu updates held in Toledo, several experts such as Ana Fernández-Sesma, professor of Microbiology at the Icahn School of Medicine at Mount Sinai in New York, and Joan Puig Barberá, from the FISABIO vaccine research area, pointed out the possibility of Yamagata’s absence.
In this sense, it should be noted that “the river is not a virus with one face, because there are different ways”, explained Adolfo García Sastre, director of Health & Global Health & Emerging Pathogens Institute of the Icahn School of Medicine at Mount Sinai in New York, in a speech given at the conference in Toledo.
What is the influenza B virus like?
Jordi Reina, from the Virology Microbiology Unit of the Son Espases University Hospital, in Palma de Mallorca, described the characteristics of this subtype in a recent article. “Globally, influenza B occurs biannually, almost always after fluctuating epidemics of influenza A, and represents about 25-30% of all influenza cases reported globally, although its percentage varies according to epidemics and geographical regions considered.
But Reina points out that “the clinical manifestations of influenza B are generally distinguishable from those caused by influenza A.” Only serology can tell what kind of flu it is. From another point he alludes to the discovery. “In 1940, an acute respiratory disease arose in children that was very similar to influenza. A new virus was isolated from these patients, which differs serologically from the already known influenza virus; the new virus was named influenza B.
One of the advantages of influenza B is that “humans are its only natural reservoir and therefore there is a possibility that it can be eradicated through an intensive and effective universal vaccination program”, the virologist explains.
Fewer cases of VRS and Covid
On the other hand, VRS and Covid do not accumulate new ones. On the other hand, the rate of Covid-19 detected in outpatient centers decreased a little after the previous week and detected cases were observed in the age group of 45-64 years. The most prevalent SARS-CoV-2 variants currently circulating are BQ.1.1 (57%), followed by BA.5 (23%).
CPV no longer massively infects children. There are now barely 9.4 cases per 100,000, having reached a peak in November at 135.3 cases per 100,000 population.
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