Study Shows Impact of Age and Pre-Existing Influenza Immune Responses in Older and Younger Adults

In an effort to understand how current influenza vaccines are influenced by preexisting immunity in people of different ages, researchers vaccinated volunteers ages 18 years to 85 years with split, inactivated Fluzone influenza vaccine in four consecutive seasons from 2013 to 2016, and assessed the impact of repeated vaccination on breadth and durability of antibodies as a result of vaccine strain changes. They found that, overall, both younger and older people have the ability to mount a breadth of immune responses following influenza vaccination.

Specifically, total IgG anti-hemagglutinin (HA) binding antibodies and hemagglutination-inhibition (HAI) activity increased in all age groups against both influenza A HA components in the vaccine postvaccination (day 21). However, younger subjects maintained seroprotective titers to the vaccine strains, which resulted in higher seroconversion rates in the elderly, since the HAI titers in elderly subjects were more likely to decline prior to the next season. Young subjects had significant HAI activity against historical, as well as contemporary H1 and H3 vaccine strains from the mid-1980s to present. In contrast, elderly subjects had HAI activity to H1 strains from all years, but were more like to have HAI activity to older strains from 1918 through the 1950s. They also had a more restricted HAI profile against H3 viruses compared to young subjects recognizing H3N2 influenza viruses from the mid-2000s to present. Vaccine recipients were then categorized by whether subjects seroconverted from a seronegative or seropositive pre-vaccination state. They found, regardless of age, immunological recall or “back-boosting” to antigenically related strains were associated with seroconversion to the vaccine strain.

According to the researchers, these findings are critical for designing the next-generation of universal or broadly protective influenza vaccines.