Being in a good mood when you get your flu jab could boost its effectiveness, according to a new study from the UK.
A team from Nottingham University looked at the moods, physical activity, diet and sleep of a group of 138 older people who were due to have their flu jab in 2014-15.
Measurements were taken three times a week over six weeks. They examined how well the jab was working by measuring the amount of influenza antibody in the blood at four weeks and 16 weeks after the jab.
They saw a link between having a positive mood, how well the jab seemed to work and higher levels of antibody, according to the study in the journal Brain, Behaviour and Immunity.
Estimates suggest that flu vaccines may only be effective in 17-53% of older adults compared to 70-90% of younger people.
Professor Kavita Vedhara, of the university's primary care division, said: "Vaccinations are an incredibly effective way of reducing the likelihood of catching infectious diseases. But their Achilles heel is that their ability to protect against disease is affected by how well an individual's immune system works.
"So people with less effective immune systems, such as the elderly, may find vaccines don't work as well for them as they do in the young.
"We have known for many years that a number of psychological and behavioural factors such as stress, physical activity and diet influence how well the immune system works and these factors have also been shown to influence how well vaccines protect against disease."