Repeated flu vaccination is highly effective in preventing severe and fatal infection caused by influenza in older adults, according to a study published in the Canadian Medical Association Journal
Aiming to evaluate the effectiveness of influenza vaccination in reducing disease severity and number of related hospital admissions, the researchers carried out a case-control study across 20 hospitals in Spain during the influenza seasons of 2013–2014 and 2014–2015.
More than 1,800 controls were matched with 728 adults aged 65 years or older who had been admitted to hospital for longer than 24 hours with laboratory-confirmed influenza. Of these, 598 inpatients had non-severe influenza, and 130 had severe influenza that resulted in eventual admission to an intensive care unit (ICU) or death.
The study found that, compared with patients who were unvaccinated in the current and previous three influenza seasons, the influenza vaccination was 31% effective in preventing admission to hospital for non-severe influenza. In patients admitted to hospital for influenza, vaccination was associated with 55% lower odds of severity of disease, 65% lower odds of admission to the ICU and 56% lower odds of death.
The number of doses of influenza vaccine over the current and three previous seasons was associated with a progressive reduction in the risk of admission to hospital for severe influenza; however, no similar trend was observed for admission to hospital for non-severe influenza.
Vaccination in the current season only did not show significant protection against severe influenza.
The authors of the study said that the results might be explained by the combination of prevented admissions to hospital for influenza and reduced disease severity in patients admitted to hospital for influenza.
They concluded that the prevention of severe and fatal infection caused by influenza vaccination may be greater than that estimated in previous studies, reinforcing the recommendation of annual vaccination for influenza in older adults.
 Casado I, DomÃnguez A, Toledo D et al. Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case-control study. CMAJ 2018 January 8;190:E3–12. doi: 10.1503/cmaj.170910