Repeated vaccination effective in protecting against severe influenza
Repeated influenza vaccination is effective in preventing severe vs nonsevere influenza infections in elderly adults, a recent multicentre, case-control study has shown.
The study included 130 and 598 patients with severe and nonsevere influenza, who were then matched to 333 and 1,493 controls, respectively.
Vaccination in the current season and at least one of the three previous seasons led to significantly lower odds of severe disease (adjusted odds ratio [OR], 0.45; 95 percent CI, 0.26–0.76; p=0.003), intensive care unit (ICU) admission (adjusted OR, 0.35; 0.17–0.70; p=0.003) and death (adjusted OR, 0.44; 0.23–0.86; p=0.02).
In comparison, those who were only vaccinated in the current season did not reduce risks of severe disease (adjusted OR, 2.22; 0.89–5.51; p=0.09) and ICU admissions (adjusted OR, 1.14; 0.34–3.87; p=0.8), and had significantly higher risk of death (adjusted OR, 3.35; 1.06–10.58; p=0.04).
Moreover, those who were unvaccinated were admitted to the ICU more frequently (16 vs 6 percent; p<0.001) compared with those who were vaccinated. Mortality rates within the first 30 days after admission were also higher in unvaccinated participants (14 vs 9 percent; p=0.04).
In terms of hospital admissions, those who were vaccinated in the current season and in any of the three previous seasons were less likely to be admitted to the hospital for nonsevere influenza (31 percent effectiveness). Effectiveness estimates were higher for preventing ICU admission (74 percent) and death (70 percent).
Furthermore, those who were vaccinated in the current season only were not significantly protected against severe influenza.