‘Less Common’ flu strain hitting children hard this flu season
Typically, influenza A dominates the influenza season. Approximately three in every four cases of the flu that is confirmed is caused by an influenza A virus. However, this season, most areas of North America are seeing an increase of cases involving the type B flu virus, a strain not typically seen in large numbers until the later months of the flu season.
Flu B can be further split into two families (B/Yamagata and B/Victoria). So far this year 98% of flu B viruses sub-typed have been from the Victoria lineage. And B strains have outpaced A strains 58% to 42%. CDC estimates that so far this season there have been at least 9.7 million flu illnesses, 87,000 hospitalizations and 4,800 deaths from flu.
Severity in children
In a special Morbidity and Mortality Weekly Reports (MMWR) report, researchers from the Centers for Disease Control and Prevention (CDC), Louisiana Department of Health and Tulane University detailed early flu activity at a large pediatric hospital in New Orleans.
The facility reported 1,268 laboratory-confirmed influenza B virus infections, including 23 hospitalizations from Jul 31 to Nov 21, 2019, a time when influenza activity is typically low. And clinic visits for influenza-like illnesses started even earlier, in mid-August, before most people had the chance to get their flu shots.
“B/Victoria viruses did not circulate widely during the past three influenza seasons, accounting for <10% of influenza virus isolates reported during the 2016–17 to 2018–19 seasons,” the MMWR report said. B/Victoria has not dominated the flu season since the 2015–2016 season so immunity to this specific flu virus is expected to be low. This low immunity could be the reason for this season’s more severe illness in children.
Last week the CDC also released a Health Alert Network (HAN) advisory, warning clinicians that in previous seasons influenza B has been associated with a higher proportion of influenza-related pediatric deaths. Because influenza activity is elevated and both influenza A and B virus infections can cause severe disease and death, the health advisory is also reminding clinicians that early treatment with antiviral medications improves outcomes in patients with influenza. So far in the 2019–20 flu season, 32 children have died, with 21 of those deaths linked to influenza B.
Though it is typically less complicated than the influenza A virus, mutating less and triggering milder symptoms, it seems to be particularly risky for children (especially those under five or with a chronic health condition). Studies show higher pediatric mortality associated with influenza B than A. While the B strain hits children the hardest, its effects are less severe on the elderly. Because of that, the most recent CDC update predicts that there could be fewer hospitalizations and deaths overall from the flu this year.
Vaccines and antivirals
Flu vaccination is always the best way to prevent flu — both influenza A and influenza B — and its potentially serious complications. And no, it isn’t too late in the season. Antiviral medications are an important adjunct to flu vaccine in the control of influenza. Almost all (>99%) of the influenza viruses tested this season are susceptible to the four FDA-approved influenza antiviral medications recommended for use in the U.S. this season.