Influenza Season Update
The 2025 influenza season is underway, and a new vaccine was introduced in the U.S. this September. Since influenza viruses can easily mutate, it’s necessary to revise vaccines each year. Fortunately, the initial reports this year look promising; the vaccine seems to closely align with the circulating flu strain.
This optimism is based on data from countries in the Southern Hemisphere, where winter arrives earlier than in the U.S. This timing allows us to glean insights into what might happen here. This year, the match rate between the vaccine-derived strain and the circulating virus was around 98%, which is remarkably close.
A good match is just one aspect influencing the effectiveness of these vaccines. Unfortunately, various real-world factors can diminish their impact. Historically, effective years see vaccine success rates ranging from 50% to 60% in preventing medical visits or hospitalizations. So far, this trend seems to hold true.
Looking back at past flu seasons that started under similar conditions can provide some insights for this one. In the 2022-23 and 2023-24 seasons, vaccine efficacy hovered around 50%. In stark contrast, the 2017-18 season saw a much lower efficacy rate of about 10%, and that year was quite severe—resulting in around 50,000 deaths and 1 million hospitalizations, almost double that of more effective years.
Even in seasons deemed successful, vaccines can’t completely eliminate the flu—but they can ease its severity. Current evidence suggests that getting vaccinated this year might significantly reduce hospital stays and fatalities, especially among high-risk groups: the elderly, very young children, pregnant women, and individuals with ongoing health conditions. This vaccine has the potential to save many lives.
A common inquiry concerns whether this year’s vaccines have thimerosal, a mercury-based ingredient found in some flu shots. Recently, Secretary of Health and Human Services Robert F. Kennedy Jr. announced that all vaccines will be thimerosal-free starting with the 2026-27 flu season.
Before this announcement, the majority of flu shots administered in the United States did not contain thimerosal, and this trend continues this year. However, certain settings, primarily public health clinics and workplace vaccination events, might still use multi-dose vials that contain it. Patients interested in a thimerosal-free option may need to ask for that specifically and arrange alternate options accordingly.
Childhood vaccination requirements can differ widely. No state mandates the flu vaccine for K-12 students, though some states like Connecticut, Rhode Island, and New York City do require it for children in daycare or preschool. Regardless of any mandates, most private insurance plans, Medicaid, and Medicare generally cover flu vaccinations as preventive care.
The flu vaccine serves as a reminder that vaccines are not universally effective. Each type offers varying degrees of community health benefits. Some vaccines primarily safeguard individuals, while others protect the wider population. Understanding these distinctions can help inform our decisions surrounding vaccinations.
Public health officials have effectively communicated the flu vaccine’s benefits without exaggeration, allowing people to make informed choices. The fact that flu shots are voluntary, yet widely accepted, highlights how trust and transparency can be as impactful as mandates.
