Journal: Repeated annual influenza vaccination and vaccine effectiveness: review of evidence

Reasoning:

• Since it is not flu season (in June), patient was really surprised and at first in denial that she had the flu
• She stated that she had the flu vaccine and though that it would protect her against the flu
• Patient wants to know whether she should still be vaccinated against the flu and whether repeated vaccination would affect subsequent vaccine protection

Purpose:

• The purpose of this systematic review/meta-analysis is to explain the historical context behind the effects of repeated vaccinations, discuss recent immunogenicity studies, and to propose another research agenda to address patient knowledge gaps
• A meta-analysis was also conducted to “evaluate the effects of prior season vaccination on current season vaccine effectiveness (VE) by type/subtype”

Methods:

• Two databases were utilized: MEDLINE and EMBASE to screen through 4636 initial articles to include 17 final articles
• Studies were conducted in outpatient, inpatient, and in community settings
• Primary analysis included studies from all seasons without any age restrictions

Key Points:

• Repeat vaccination may adversely affect vaccine-induced serological response and vaccine effectiveness in certain seasons, especially for H3N2
• This finding is consistent with multiple studies that demonstrate that repeated vaccination could blunt the H1 antibody response to vaccine strains
• Heterogeneity was found in repeated vaccination effects, which is not surprising given the variability in immune response of different age groups and populations
• The antigenic distance hypothesis predicts that there is variability in each flu season’s antigenic exposures
• Additionally, egg-based manufacturing processes could introduce antigenic mutations and growth reassortant viruses that are used for widespread production

Conclusion:

• We need to maintain public confidence in vaccines, especially at this time
• Current research regarding our understanding of repeated vaccinations is not enough to inform or change current vaccination recommendations, thus it is important to still receive yearly flu vaccines, regardless of whether the patient got the flu or not

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