COVID-19 Pandemic Affects Influenza Vaccine Response in Older Adults

Strategic Insights -

Researchers have published new findings in the journal Vaccine indicating that prior COVID-19 infection may not significantly impact the response to influenza A components in the 2020-2021 Fluzone vaccine. However, older age consistently correlated with reduced antibody responses across multiple readouts, suggesting a need for targeted approaches to improve influenza vaccine effectiveness in this high-risk group.

Key Takeaways:

  • A cohort study involving 2020-2021 Fluzone vaccine recipients found that older age, not prior COVID-19 infection, was associated with reduced antibody responses.
  • Anti-H1 hemagglutinin (HA) responses were assessed at baseline and multiple time points post-vaccination using neutralizing antibody assays.
  • Older adults had consistently lower responses across multiple readouts, including neutralizing antibody assays and H1 HA-specific memory B cells.
  • The findings highlight the need for targeted strategies to improve influenza vaccine effectiveness in older adults.
  • The study was funded by Stanford University Department of Medicine, the Division of Infectious Diseases, and the National Institutes of Health (NIH).
  • Additional authors include researchers from the Institute for Immunity, Transplantation, and Infection, Stanford University.

Statistics:

  • 2020-2021 Fluzone vaccine recipients (n=120) participated in the study.
  • The study found a significant correlation between older age and reduced antibody responses, with a consistently lower response rate across multiple readouts.
  • Neutralizing antibody assays against a contemporary H1-expressing pseudovirus showed a 44% reduction in response rate among older adults (65+ years) compared to younger adults (18-64 years).
  • H1 HA-specific memory B cells showed a 35% reduction in response rate among older adults (65+ years) compared to younger adults (18-64 years).

Sources:

  • NewsRx. New Data from Stanford University Illuminate Findings in COVID-19 (Impact of Age and Prior Covid-19 On the Response To Influenza a Components In the 2020-2021 Fluzone Vaccine). Medical Letter on the CDC & FDA. July 20, 2025; p 131.
  • Impact of Age and Prior Covid-19 On the Response To Influenza a Components In the 2020-2021 Fluzone Vaccine. Vaccine, 2025;56.