Debate on annual influenza vaccination in healthcare workers for the same subtype under the vaccine shortage

Background: Influenza vaccination is the primary method for preventing influenza and its severe complications. Healthcare workers (HCWs) are one of the priority groups for the influenza vaccination. Objectives: To determine whether healthy HCWs, who were vaccinated with the same subtype for the two previous years, could be given less priority for influenza immunization under the vaccine shortage. Study design: We measured hemagglutination-inhibition antibody titers from sequential serum samples in 50 pre-immune subjects and 50 age-matched vaccine-naive subjects: immediately prior to the administration of the vaccine, 4-6 weeks, and 6 months after the vaccination. Results: Prevaccination titers were maintained above protective level and high protection rates were observed for all three strains in pre-immune subjects: A/H1N1, A/H3N2, and B strains. As for the sequential changes, the protection rates for all three strains still remained above 70% until 6 months following the vaccination. Conclusion: Skipping influenza vaccination for a year could be considered in healthy pre-immune HCWs under the epidemic of the same subtype as two previous years.