As the holiday season unfolds, the flu season in the United States is gaining momentum, largely due to a new variant known as subclade K. According to the US Centers for Disease Control and Prevention (CDC), the proportion of doctor visits for flu-like symptoms rose to 3.2% during the week ending December 6, 2023. This figure exceeds the national baseline, indicating that flu season is officially underway.
Navigating the onset of flu season involves two primary methods: calendar timing and flu activity. Dr. Caitlin Rivers, who leads the Center for Outbreak Response Innovation at the Johns Hopkins Bloomberg School of Public Health, noted that while the calendar marks week 40 (around early October) as the start, actual flu activity is a more reliable marker. With 14 public health jurisdictions reporting moderate to high flu activity, particularly in the Northeast, the situation is becoming increasingly concerning.
New York City is experiencing particularly high levels of flu activity, as are New Jersey, Louisiana, and Colorado. Alarmingly, this week also marked the first reported death of a child from flu this season in the United States. Dr. Tim Uyeki, chief medical officer of the CDC’s influenza division, emphasized the importance of vaccination at this critical juncture.
Indicators of a Severe Flu Season
The current flu season may be shaping up to be more severe than usual. Dr. James McDonald, commissioner of the New York State Department of Health, reported that flu cases are rising earlier than typical, with hospitalizations doubling in the last two weeks. He described the rise as a “J-shaped curve,” suggesting a rapid increase in severe cases compared to the previous year. The state has alerted hospitals to the swift uptick in cases and the need for stringent infection control measures.
The majority of flu viruses analyzed thus far have been identified as subclade K, a variant of the H3N2 strain of influenza A. Historically, flu seasons dominated by H3 viruses tend to be more severe, particularly affecting older adults. Countries such as Japan, China, the UK, and Canada are also reporting busy flu seasons, with Australia setting a record of nearly 500,000 confirmed cases this year.
Although some experts caution that the United States may not mirror the severity seen in other regions, the presence of a new variant complicates predictions. Dr. Jennifer Nuzzo from Brown University remarked that while consecutive bad flu seasons are uncommon, the unpredictability of flu patterns is well-known among public health experts.
Vaccination and Public Health Measures
The current flu vaccines do not target subclade K, as it emerged after strain selection for this year’s shots. However, studies from the UK’s Health Security Agency indicate that the vaccines still provide substantial protection against H3N2 strains, reducing emergency department visits and hospitalizations by nearly 75% in children. For adults, particularly those over 65, effectiveness ranges from 30% to 40%.
Dr. Alex Greninger from the University of Washington emphasized the importance of vaccination, especially for children, who typically have less immunity. With only 38% of children vaccinated this year—lower than previous seasons—public health experts are urging families to act quickly. The CDC reported a record of 280 child deaths from flu last season, underscoring the need for vigilance.
While flu shots cannot completely prevent infection, they significantly reduce the likelihood of severe illness and hospitalization. Dr. Rivers recommends additional precautions, such as wearing masks in crowded spaces during peak infection periods and improving ventilation in shared environments. The flu presents with sudden symptoms including high fever, cough, and body aches, making early testing and treatment crucial.
As the flu season progresses, experts continue to monitor trends closely, urging the public to prioritize vaccination and take proactive steps to mitigate the spread of illness.