New research suggests that the very low circulation of influenza since the onset of the health crisis has led to the disappearance of two different strains of the virus. Explanations.
An unprecedented situation
Due to the pandemic of Covid-19, influenza cases have reached historic lows. A phenomenon that experts attribute to the wearing of face masks as well as to the various social distancing measures put in place to limit the spread of the coronavirus. Recent reports have revealed that there have been no cases worldwide for at least a year for two types of influenza viruses.
Although experts do not know if these strains are actually extinct, such a situation could make the design of the seasonal flu vaccine easier, by restricting the number of strains to be included.
In order to determine which influenza viruses may have disappeared, it is essential to understand how they are classified. Two families of influenza viruses are the cause of seasonal influenza: influenza A and the flu B. Viruses influenza A are divided into ” subtypes »Based on two proteins present on their surface, hemagglutinin (H) and neuraminidase (N). Currently, viruses H1N1 and H3N2 circulate in humans, and each of these subtypes is subdivided into ” clades ».
Viruses flu B, on the other hand, do not have subtypes or clades, but are divided into two lineages called B / Yamagata and B / Victoria. A clade of H3N2, known as 3c3.A, has not been detected since March 2020, and the same goes for the lineage B / Yamagata.
“The spectacular drop in the number of cases this year will definitely have an impact on the diversity of influenza viruses”
Every year, the flu vaccine is developed before the flu season begins. To do this, scientists look at the strains circulating around the world and determine which ones will be most common in the months to come. Lower diversity of the influenza virus means a smaller number of viruses to consider, and by extension a greater chance that the strains selected for the compound will match those in circulation.
Viruses H3N2 constitute a particularly diverse group and, before the pandemic of Covid-19, their clades seemed to diversify genetically every year. A decrease in the diversity of this subtype would therefore be a ” excellent thing “, According to Richard Webby, of the’WHO.
« Even though they haven’t been reported in official databases, these types of viruses may still exist, but the dramatic drop in the number of cases this year is definitely going to impact the diversity of influenza viruses. », He believes. ” The magnitude of the change and its duration are the big question marks. But we’ve never seen this before. »