US Faces Potential for Two Flu Seasons Amidst Early West Coast Surge
A mutated H1N1 strain is driving an unusually early increase in flu cases, raising concerns of a second wave later in the winter.
The United States may experience two distinct flu seasons this winter, a scenario experts say is being driven by an early surge in cases on the West Coast attributed to a mutated strain of the H1N1 influenza virus. This early uptick is occurring more than two months ahead of the typical flu season timeline.
Dr. Alexander Greninger, head of the Division of Infectious Disease Diagnostics at the University of Washington's Department of Laboratory Medicine, suggested that the current rise in cases could peak soon, potentially followed by a second wave in January, February, or March stemming from an as-yet-unknown variant. Typically, flu activity begins in October, peaks between December and February, and subsides by May, with initial increases usually seen in Southern states before spreading.
However, data from the Centers for Disease Control and Prevention (CDC) indicated that flu levels began rising in the week ending August 8, with the West Coast experiencing an unexpected surge. In some parts of California, about one in 10 individuals are now testing positive for the flu. Greninger noted that his lab is seeing flu levels in Seattle comparable to what is usually observed in January.
Nationally, flu test positivity rates have increased, with 5.7% of tests collected during the week of October 17 coming back positive, up from 5% the previous week and 3.9% two weeks prior. Hospital admissions for respiratory illnesses have also risen, with 4,811 patients admitted in the past week compared to 4,024 the week before and 2,572 two weeks prior. The CDC reports that H1N1 is the most frequently identified strain.
The H1N1 strain responsible for the 2009 swine flu pandemic, which caused widespread illness and hospitalizations, is also circulating this year. While this strain is included in the current flu vaccine, a new mutation, G155E, may reduce the effectiveness of existing antibodies from vaccines in recognizing and fighting it. This mutation is believed to be contributing to the early and rapid spread.
Cases have seen increases in 16 states, including Alaska, Oregon, Arizona, and Florida. Two states, Louisiana and Hawaii, are reporting moderate flu virus levels, with the rest of the country experiencing low or minimal levels. Experts have observed the spread moving eastward from the Pacific states, impacting all regions of the country.
Health officials are urging Americans to get vaccinated as soon as possible, ideally before Halloween, to ensure maximum protection throughout the season. Greninger advised that while many people wait until late October to get their flu shot, the optimal time for vaccination was two to three weeks prior to receiving it, allowing the body time to build immunity.
Previous seasons have seen dual waves of influenza. The 2021-2022 season experienced a peak in late December 2021 and another in April 2022, while the 2018-2019 season had peaks in December 2018 and March 2019.
Influenza, a highly contagious respiratory infection, typically affects about 8% of the U.S. population annually, causing symptoms such as fever, cough, and fatigue, and can lead to severe complications like pneumonia. Annual vaccination is recommended to reduce the risk of infection and its severity. The flu shot, updated each year to target prevalent strains, protects against influenza types A and B, which are the most common and severe types.