Vaccines for preventing influenza in the elderly

Influenza vaccination with a well-matching vaccine appears to be effective in reducing clinical influenza, serologically confirmed influenza, pneumonia and hospital admissions for respiratory illness, but the effect is highly variable in different settings, and the evidence from high-quality studies is insufficient on total mortality.

A Cochrane review included 75 studies with people of 65 years or older. Five of the trials were RCTs, 51 were cohort-studies and 12 case-control studies. A total of 68 studies were used to assess efficacy (they were split into subsets by influenza season or setting or vaccine type, resulting in 100 data sets) and 8 to assess safety (one RCT was included in both assessments). In the RCTs placebo was the comparison and all cohort studies compared the effects of vaccination against no vaccination.

• RCTs: Allthough the heterogeneous nature of the vaccines tested (monovalent, trivalent, live, or inactivated aerosol vaccines), setting, follow up and outcome definitions makes firm conclusions difficult, influenza vaccines appear to decrease serologically confirmed and clinical influenza.
• Cohort studies in long-term care facilities: The overall effectiveness of vaccines against influenza-like illnesses was 23% (6% to 36%) when vaccine matching was good and not significantly different from no vaccination (RR 0.80; 95% CI 0.60 to 1.05) when matching was poor or unknown.
• Studies recorded during outbreaks or periods of high viral circulation: The effectiveness of the vaccines in preventing pneumonia was assessed in 13 data sets. Well-matched vaccines were 46% (30% to 58%) effective in preventing pneumonia (8 studies). When matching was poor or unknown vaccines had no effect (RR 0.68; 95% CI 0.39 to 1.21, 5 studies). Vaccination had a significant effect on the prevention of deaths due to influenza or pneumonia (20 data sets).
• Studies carried out during low viral circulation: The vaccines were 33% effective (2% to 54%) in preventing influenza-like illnesses but did not have a statistically significant effect in preventing influenza (RR 0.23, 95% CI 0.05 to 1.03; 2 data sets, 691 observations).
• Cohort studies in community-dwelling elderly: Inactivated influenza vaccines were not effective against influenza-like illnesses, influenza or pneumonia.
• Case-control studies: Before adjustment, in community-dwelling elderly inactivated influenza vaccines were associated with an increased risk of admission for any respiratory disease (OR 1.08; 95% CI 0.92 to 1.26; 20 582 observations) and did not prevent hospital admission for influenza and pneumonia in elderly individuals living in the community (OR 0.89; 95% CI 0.69 to 1.15; 1 074 observations) or affect hospitalisation for influenza-like illness or affect mortality from influenza and pneumonia. After adjustment, however, the vaccines did reduce the risk of death from influenza and pneumonia (OR 0.74; 95% CI 0.60 to 0.92) and prevent admission for influenza and pneumonia (OR 0.59; 95% CI 0.47 to 0.74) and for all respiratory diseases (OR 0.71; 95% CI 0.56 to 0.90).

The effectiveness of inactivated influenza vaccines in elderly individuals seems to be modest, irrespective of setting, outcome, population and study design. However, a significant residual heterogeneity was noted among studies that could be explained only in part by different study designs, methodological quality, settings, viral circulation, vaccine types and matching, age, population types and risk factors. The residual heterogeneity could be the result of the unpredictable nature of the spread of influenza and influenza-like illness and the bias caused by the non-randomised nature of our evidence base. Therefore, the available evidence is of poor quality and provides no firm guidance regarding the safety, efficacy or effectiveness of influenza vaccines for people aged 65 years or older.

Comment: The quality of evidence is downgraded by study limitations (poor reporting, loss to follow-up) and indirectness (high-risk patients mostly excluded), but upgraded by consistency of results in a large number of observational studies.

The following decision support rules contain links to this evidence summary:

• Influenza vaccination for the elderly

Ədəbiyyat

1. Jefferson T, Di Pietrantonj C, Al-Ansary LA, Ferroni E, Thorning S, Thomas RE. Vaccines for preventing influenza in the elderly. Cochrane Database Syst Rev 2010 Feb 17;2:CD004876.