Influenza experts say there are some worrying indicators that this year's flu season could be particularly virulent, though they do not know whether those indicators necessarily mean there will be a widespread flu outbreak in the Northern Hemisphere.
According to STAT News, experts have noted that countries in the Southern Hemisphere had experienced a particularly virulent flu season during the hemisphere's 2017 winter and are concerned the Northern Hemisphere will experience a similar season.
Kanta Subbarao, director of the World Health Organization's influenza collaborating center in Australia, said, "At this point the data look like it was a big season. Started earlier than usual, lasted a bit longer. … And all segments of the population were affected, including people who were vaccinated."
According to STAT News, the cases largely were caused by H3N2 viruses, and experts say that flu seasons dominated by such viruses usually include a significant number of flu-related hospitalizations and an increased number of flu-related deaths.
However, according to STAT News, North America last winter had a considerably active flu season, with cases mainly stemming from H3N2 viruses, and it is less likely for individuals affected by the viruses last flu season to be affected again this flu season. Jacqueline Katz, deputy director of CDC's influenza division, said that immunity could help to curb how virulent the flu is this season.
Still, Danuta Skowronski, a flu expert at British Columbia's Center for Disease Control, said occasionally areas do have back-to-back seasons dominated by H3N2, and that subsequent waves of H3N2 sometimes can be more virulent proceeding seasons. Skowronski added, "The bottom line is you should never say never with influenza."
In addition, the upcoming flu season could be driven more by H1N1 viruses, "which tend to cause less severe outbreaks," STAT News reports. The Northern Hemisphere also could experience a mixed flu season, meaning it could experience strains of both H3N2 and H1N1, according to STAT News.
Daniel Jernigan, who directs CDC's influenza division, said a few mixed flu seasons have occurred in recent years, adding, "It could be if that trend follows that maybe we'll have an H1N1 year."
Vaccine might not be an ideal match
Flu experts also raised concerns that this year's flu vaccine could be ineffective against strains predicted to circulate this flu season, including that vaccine's H3N2 component.
Skowronski said, "Don't consider yourself invincible if you received the vaccine. Because there are signals to be concerned about in terms of the possible [H3N2] protection this season."
Skowronski recommended that individuals with weakened immune systems should consider asking their health care providers for advanced prescriptions of antiviral drugs that they could fill quickly if they contract the flu.
In addition, experts say some evidence suggests that individuals who were vaccinated for the flu in previous seasons might be more susceptible to contracting the flu in upcoming seasons, because their bodies as a result of previous vaccinations produce fewer antibodies to the viruses for which they were vaccinated. According to STAT News, the Northern Hemisphere's most recent flu vaccine included the same H3N2 component that is used in this year's flu vaccine, so people who were vaccinated last year might end up more susceptible to the flu this year if the seasons is driven by H3N2 viruses and their bodies produce fewer antibodies as a result of previous vaccination. Skowronski said, "It will be an interesting year from many perspectives" (Branswell, STAT News, 10/16).
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