LAUSR

Human influenza viruses passaged in eggs often acquire mutations in the hemagglutinin (HA) receptor binding site (RBS). To determine if egg-adapted H1N1 vaccines commonly elicit antibodies targeting the egg-adapted RBS of HA, we completed hemagglutinin-inhibition assays with A/California/7/2009 HA and egg-adapted A/California/7/2009-X-179A HA using sera collected from 159 humans vaccinated with seasonal influenza vaccines during the 2015-16 season. We found that ∼5% of participants had ≥4-fold higher antibody titers to the egg-adapted viral strain compared to wild type viral strain. We used reverse-genetics to demonstrate that a single egg-adapted HA RBS mutation (Q226R) was responsible for this phenotype.