Why flu shot protection declines as we age

Once you grow old, flu vaccine gets less effective and now, a team of researchers has explained why it is so.

More broadly, the findings reveal novel molecular signatures that could be used to predict which individuals are most likely to respond positively to vaccination.

Co-senior study authors Shankar Subramaniam of the University of California, San Diego and Bali Pulendran of Emory University said that by providing a more complete picture of how the immune system responds to vaccination, the findings may help guide the development of next-generation vaccines that offer long-lasting immunity and better protection of at-risk populations.

In the study, within one week of flu vaccination, young individuals showed high levels of antibody-producing B cells, whereas the elderly showed high levels of immune cells called monocytes, which elicit inflammatory responses in the body. These age-related differences predicted impaired vaccine-induced immune responses observed in the elderly three weeks later.

"Together, these results suggest potential mechanisms by which changes to the innate response in the elderly may result in diminished antibody responses to vaccination," Subramaniam says.

The researchers urged caution against over-generalizing their new findings.

The study appears in Immunity.