The Timing of Flu Shots: A Critical Review

As flu season approaches, many healthcare workers face a dilemma: receive the annual flu shot by the end of October or get vaccinated early, despite the evidence suggesting that effectiveness over time decreases in high-risk individuals. A substantial body of research indicates that antibodies produced in response to flu vaccinations reach their highest levels just a few weeks after vaccination, only to begin dropping right as the winter influenza peak approaches. Meanwhile, tens of millions of Americans heed public health messaging to get vaccinated as soon as possible, even starting in September. This narrative raises critical questions about the Centers for Disease Control and Prevention's (CDC) recommendations and the potential consequences of encouraging early vaccination.

Key Takeaways:

• The CDC's focus on vaccine uptake may lead to a conflict with their true goal: preventing severe illnesses. Public messaging encouraging early vaccination may result in less overall protection when it is most needed in the winter.
• One study suggests that starting the annual vaccine campaign in October instead of September could reduce flu-related hospitalizations by 3-4% in years where flu cases peak in January or February.
• This reduction could mean up to 10,000 fewer hospitalizations, but it requires a concerted effort to achieve high vaccination rates in a shorter period.
• Currently, the CDC has not delayed its annual flu shot campaign, despite the potential benefits of a delayed start.
• Researchers should begin studies to assess the effectiveness of a two-dose flu vaccine for high-risk populations, like seniors and the immunocompromised, which would better protect them throughout the flu season.
• The Covid-19 vaccine experience has taught us that boosting high-risk individuals even just a few months apart can significantly decrease hospitalizations associated with Covid-19.

Statistics:

• 25% of seniors in the United States have received their annual flu shots.
• New from the recently concluded flu season in the Southern Hemisphere show that this year's flu shot was 35% effective at preventing hospitalizations.
• Effectiveness varied by age and other risk factors, with 31% effectiveness in older people and 59% effectiveness for young adults with medical comorbidities.
• In the first week of October last year, weekly flu-related hospitalizations were over 44 times higher than they were at their eventual peak, which occurred in late December.

Sources:

• "The Centers for Disease Control and Prevention recommend people get vaccinated early, but epidemiologists argue it's better to focus on a more metrics, such as the percent of severe illnesses averted." (no specific publication date)
• "New from the recently concluded flu season in the Southern Hemisphere show that this year's flu shot was 35 percent effective at preventing hospitalizations." (no specific publication date)
• "Jeremy Faust is a doctor in the emergency medicine department at Brigham and Women's Hospital." (no specific publication date)
• Biel Alino/EPA, via Shutterstock (no specific publication date)