Flu activity in the US is increasing earlier than usual, but so far remains low. In the week ending October 3, 3.6% of samples tested in clinical laboratories tested positive for influenza, the Centers for Disease Control and Prevention reported.
A week earlier, positive samples were 3.4%. The data show a gradual increase since late August and early September, with the highest activity on the West Coast of the US. Despite the earlier start, the indicators are still within the expected seasonal fluctuations.
H1N1 is the leading virus at the beginning of the season
204 influenza viruses have been reported in public laboratories for the last observed week. 201 of them are type A and three are type B. Of the 127 type A viruses typed, 125 are H1N1pdm09, or 98.4%, while two are H3N2.
This is a change from previously published data for the week ending September 26, when H1N1 accounted for 96% of typed influenza A samples. The Centers for Disease Control and Prevention clarified that the early dominance of one subtype does not mean that it will remain dominant for the rest of the season.
Usually, flu activity begins to increase in October and November, and most often peaks between December and February. The 2026-2027 season is projected to be moderate in severity, but confidence in this estimate is low to moderate.
October remains a good time to get vaccinated
A flu shot is recommended for everyone over the age of 6 months. The Centers for Disease Control and Prevention says most people should get the shot before the end of October, as it can take about two weeks to build full protection.
He says getting vaccinated too early in the summer months can lead to a weakening of protection before the end of flu season. Vaccine effectiveness against a medically necessary illness has ranged from 29% to 56% over the past decade, according to the Centers for Disease Control and Prevention. The vaccine does not prevent every infection, but it is more effective at limiting severe illness.
Who are the risk groups?
Children under 5, people over 65, pregnant women and patients with chronic diseases are at greater risk of complications. Possible complications include pneumonia, sepsis, and inflammation of the brain or heart muscle.
Schaffner emphasizes that the spread of flu on the West Coast is not unusual and does not in itself indicate that the season will be more severe. Whether the early surge will develop into a widespread flu wave will become clearer in the coming weeks' reports.
Sources: dunavmost.com, livescience.com