"Repeated vaccination for influenza is highly effective in preventing severe and fatal infection caused by influenza in older adults," said Itziar Casado, researcher at the Instituto de Salud Pública de Navarra in Spain.
‘People were observed over four seasons - to determine whether repeated vaccinations result in reduced severity of influenza.’
For the study, published in CMAJ (Canadian Medical Association Journal), the team looked at the effect of repeated influenza vaccinations in the current and three previous seasons in people aged 65 years and older admitted to 20 hospitals to determine whether repeat vaccination reduced severe influenza.
The study also adds to findings from previous research that shows influenza vaccination reduces severity of the illness.
"Because severe cases of influenza may be prevented by two mechanisms, the effectiveness of vaccination against severe influenza may be greater than that for mild cases, and the benefit of influenza vaccination may be greater than that estimated in previous studies," the researchers said.
The prevention of severe and fatal infection caused by influenza was observed mainly in patients who were vaccinated in both the current and previous seasons, which reinforces the recommendation of annual vaccination for influenza in older adults, the study noted.