Americans Cough and Sneeze as This Year’s Flu Season Starts Unusually Early

Flu season has started unusually early in the U.S., mainly on the West Coast and even in Washington state, which is atypical. According to the Centers for Disease Control and Prevention (CDC) in Atlanta, cases began rising sharply 2.5 months earlier than usual. That does not mean the same must happen in Europe.

This year’s increase in influenza virus activity in the United States was already recorded in late August and in September. It is now spreading mainly along the West Coast, in California, Arizona and Utah, as well as in Seattle and Washington state, which is the most surprising part.

The seasonal wave of flu cases in the U.S. usually begins in the South, most often in Florida, and then gradually moves north. In Seattle, however, infection levels in October are already what is normally seen in January, Dr. Alex Greninger, head of the Infectious Disease Diagnostics division at the University of Washington, told CNN.

The reason is the virus’s spread from Asia to the U.S. West Coast. In California, Arizona, Nevada and Washington state, one in 10 flu tests comes back positive. According to the CDC in Atlanta, however, increases in infections are being recorded more and more often east of the West Coast.

It is concerning that the flu vaccine prepared for the current 2026/2027 season may not be as effective as expected. It covers three strains of the virus: A(H1N1), A(H3N2) and B (the B/Victoria lineage). Research shows, however, that the A(H1N1) strain, which first appeared in 2009, has recently mutated (designated G155E). Because of this, children and adolescents who have not yet encountered this variant may be more susceptible to it.

The A(H1N1) strain with the G155E mutation appeared earlier in Japan, where children were its main victims; some schools had to be closed. In the U.S., this variant now accounts for 96-98 percent of all confirmed flu cases.

The G155E mutation allows the flu virus to partially evade existing population immunity. That does not mean this year’s flu vaccine is ineffective. It may offer less protection against infection, but it still reduces the risk of a severe course of the disease, which is always the main goal of vaccination, especially for respiratory infections.

It is very difficult to forecast how the flu epidemic will develop. The fact that the U.S. recorded an increase in cases so early this season does not mean the same must happen in Europe. Dr. Alex Greninger expects that a second wave of cases may appear in the U.S., this time in early 2027, as in previous flu seasons. The most important thing is to get a flu shot as soon as possible.

Zbigniew Wojtasiński (PAP)