But that second wave never came—just one of a few oddities tracked during the 2022-23 flu season. In fact, it was the first time in Walgreens surveillance history, which began in 2018, that the Walgreens Flu Index did not show a second wave of flu.
"It's not unusual to see a surge in cases of influenza B later in the season, but we've really seen no evidence of that this year,” says Anita Patel, vice president of pharmacy services development at Walgreens.
So, why was there no second wave? Patel says it could be because vaccines and circulating flu strains were reasonably well matched this season.
"According to data shared by the CDC, this season’s flu vaccine effectiveness against the predominant H3N2 viruses was 45% among children, which has been around 30% during previous seasons," she says. Additionally, vaccinated adults aged 18 to 64 were 51% less likely to have a flu-related hospitalization, the CDC reports.
Another strange thing about this year's flu season: a very early start. The Walgreens Flu Index began tracking flu activity as early as August, which is far earlier than usual. As flu cases climbed in the fall, Patel noted that people were more vulnerable to respiratory infection as they returned to pre-pandemic activities and spent more time indoors without a mask or social distancing.
Even though this flu season was unique, Patel says the resulting illnesses, hospitalizations and deaths from flu matched up with pre-pandemic seasons—no second wave needed.
“So far this season, the CDC estimates there have been at least 26 million illnesses, 290,000 hospitalizations and between 19,000-56,000 deaths from flu, so despite the absence of a second wave, this burden of disease is in line with previous pre-pandemic seasons,” Patel says.The Walgreens Flu Index is an interactive tool that allows users to search by market or state to see where their geographic area ranks for flu activity in any given week. For more information about the Walgreens Flu Index, or to view it for yourself, check out the Walgreens Flu Index page in the Walgreens Newsroom.