Influenza Antibody Levels Associated with Laboratory-Confirmed Influenza in a Test-Negative Study Design, US Flu VE...

Area of Science:

• Immunology
• Virology
• Epidemiology

Background:

• Assessing the relationship between antibody concentrations and confirmed influenza virus infection in outpatients.
• Utilizing a test-negative study design to evaluate influenza virus infection.
• Focusing on antibody levels within 7 days of symptom onset.

Purpose of the Study:

• To determine the association between antibody titers and the odds of laboratory-confirmed influenza.
• To investigate the protective effect of different antibody types (HI, MN, NAI) against influenza.
• To analyze these associations in adult outpatients with acute respiratory illness.

Main Methods:

• Collected serum and respiratory specimens from outpatients with acute respiratory illness across five states (Nov 2018-May 2019).
• Tested respiratory specimens for influenza virus and identified viral clades via genomic sequencing.
• Measured antibody titers using hemagglutination inhibition (HI), microneutralization (MN), and neuraminidase inhibition (NAI) assays, analyzed with logistic regression.

Main Results:

• Higher HI, MN, and NAI antibody titers against circulating viruses correlated with reduced odds of confirmed influenza.
• Each two-fold increase in specific antibody titers showed significant reductions in odds for both Influenza A(H1N1)pdm09 and A(H3N2) infections.
• Neuraminidase inhibition (NAI) titers demonstrated an independent association with lower odds of infection for both influenza A strains, even after accounting for HI titers.

Conclusions:

• Elevated influenza antibody titers against currently circulating strains are associated with a decreased likelihood of infection.
• This finding supports the role of humoral immunity in protection against influenza virus infection in adults.
• The study highlights the utility of different antibody assays in assessing influenza protection.