Older adults are more likely to suffer illness and death from the flu, and they have a blunted response to influenza vaccine. A high dose flu vaccine increases the rate of seroconversion – the production of detectable flu–fighting antibodies – in older adults.

To explore the mechanism for this improved response, Mark Pilkinton, MD, PhD, Spyros Kalams, MD, and colleagues measured the activation of circulating T follicular helper (Tfh) cells in 50 adults age 65 or older who received either high dose or standard dose inactivated influenza vaccine. Tfh cells are a subset of immune system cells that help B cells, which produce antibodies.

The high dose vaccine elicited higher levels of ICOS expression, an indicator of Tfh cell activation, on circulating Tfh cells. The magnitude of increase in ICOS and Tfh activation predicted seroconversion for both influenza A and B vaccination.

The findings, reported in the Jan. 5 issue of the journal Vaccine, suggest that future vaccine studies should focus on ways to further optimize Tfh activation.