If you are planning to get a flu shot shortly, better stay in a happy mood. Researchers have found that being in a positive mood on the day of your flu jab can increase its protective effect.

The study, published in the journal Brain, Behavior and Immunity, has implications for the elderly as flu vaccination is estimated to only be effective in 17-53 per cent of older adults compared to 70-90 per cent of younger people. "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," said Kavita Vedhara, Professor at University of Nottingham in Britain. "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," she added. 

The team measured negative mood, positive mood, physical activity, diet and sleep three times a week over a six week period in a group of 138 older people due to have their flu jab.Then 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 vaccination.The results showed that positive mood over the six week observational period predicted how well the jab worked -- with good mood associated with higher levels of antibody. 

In fact, when the researchers looked at influences on the day of vaccination itself, they found an even greater effect on how well it worked, accounting for between eight and 14 per cent of the variability in antibody levels.The findings confirm a long-held view that a number of psychological and behavioural factors such as stress, physical activity and diet influence how well the immune system works.