There is an optimal time of the day to get a flu shot: the morning, according to a new study by researchers from the University of Birmingham and published in the journal Vaccine.
In the study, senior citizens who got their flu vaccines in the mornings produced higher levels of antibodies to certain flu strains than those who got their shots in the afternoon. This is especially important for people over 65, who are more likely to have weaker immune systems than the general population and are more likely to be hospitalized and die from the flu.
If the effect is confirmed in wider studies, giving seniors a shot in the morning instead of the afternoon could be an cheap, easy way to better protect them from flu and other diseases.
"A significant amount of resource is used to try and prevent flu infection each year, particularly in older adults, but less than half make enough antibody to be fully protected,” said Janet Lord, a researcher from the Institute of Inflammation and Aging at the University of Birmingham and a co-investigator on the study. "Our results suggest that by shifting the time of those vaccinations to the morning we can improve their efficiency with no extra cost to the health service."
Researchers analyzed data from the vaccinations of 276 senior citizens across 24 clinics in the U.K. who got their shots either in the morning (between 9 a.m. and 11 a.m.) or in the afternoon (between 3 p.m. and 5 p.m.) All the participants were aged 65 or older, healthy, and weren’t taking a medication that suppressed the immune system. One month after getting the vaccine, those who got their shots in the morning had significantly higher levels of antibodies for the H1N1 A-strain and B-strain, though not the H3N2 A-strain, than those who got their shots later on in the day.
While the researchers aren’t sure why getting the shot at a certain time of day appears to produce more antibodies, emerging research does suggest that the immune system’s response to “challenge” varies according to the time of day.
It also suggests different times of day might be best for different vaccines. A pilot study conducted by the researchers showed that men both young and old had a greater antibody response to hepatitis A and the A/Panama influenza strain if they got their vaccines in the morning.
And past studies show that an attenuated Venezuelan equine encephalomyelitis vaccine given at 8 a.m. produced peak antibody levels four days earlier than shots administered at 8 p.m. But a hepatitis B vaccine given between 1 p.m. and 3 p.m. resulted in a higher antibody response compared to a shot between 7:30 a.m. and 9 a.m.
Lord and her colleagues now plan to study this effect among a wider, more diverse population of seniors to include those with medical conditions like diabetes, liver and kidney disease, which can suppress the immune systems. They also have plans to test whether administering the pneumonia vaccine in the mornings might produce more antibody response in seniors.
The research is important, as there’s a significant need for more strategies on how to protect older people from influenza. Flu and pneumonia is currently the eighth most common cause of death in the U.S.