Do vitamins A and D help the flu vaccine work better? It depends.

Vitamins A and D influence the immune system. Researchers suspected these vitamins might affect how well children respond to the flu vaccine. But earlier studies by other scientists showed mixed results.

A new St. Jude study may have the answer. Baseline vitamin levels are rarely studied in flu vaccine research. But scientists found that baseline vitamin A and D levels were linked to immune responses to the vaccine.

A clinical trial studied the flu vaccine and vitamin supplements in children 2–8 years old. Children got two doses of the vaccine either with a vitamin A and D supplement or a placebo.

“Baseline vitamin A and D levels each influenced the flu vaccine-induced immune response and the effect of high-dose vitamin supplements,” said Julia L. Hurwitz, PhD, of the St. Jude Department of Infectious Diseases.

A report on this work appeared in Viruses.