Key Point

Influenza vaccinations have modest effectiveness in elderly people living in long-term care facilities and even less effectiveness in those in the community. Reliable evaluation of the effects of influenza vaccines was hampered by the lack of randomized controlled trials.

ALESSANDRIA, ITALY—Influenza vaccinations are modestly effective among elderly people in long-term care facilities and even less effective among those in the community, according to epidemiologist Tom Jefferson, MD, and colleagues.¹

The researchers analyzed data from 64 studies (96 data sets representing 96 influenza “seasons”) comparing vaccination with any influenza vaccine versus placebo or no intervention in people age 65 or older. Half the data sets reported A/H3N2 viral circulation, while the remaining involved B, A/H1N1, or A/H2N2 viruses, or an unspecified virus.

OVERALL EFFECTIVENESS

Dr. Jefferson and his colleagues at the Cochrane Vaccines Field in Alessandria, Italy, determined that “the overall effectiveness of vaccines against influenza-like illness was 23% when vaccine matching was good, and not significantly different from no vaccination when matching was poor or unknown.” Well-matched vaccines were effective for the prevention of pneumonia (46%) and hospital admission for influenza or pneumonia (45%); poorly matched or unknown vaccines were not effective. Well-matched vaccines were also effective for the prevention of deaths due to influenza or pneumonia, whereas poorly matched or unknown vaccines were not.

EFFECTIVENESS IN LONG-TERM CARE FACILITIES AND IN THE COMMUNITY

According to the researchers, 11 data sets assessed the effects of influenza vaccines in 350 institutional facilities during low viral circulation. Results showed that vaccination prevented influenza-like illnesses, but not influenza. In addition, four data sets involving low viral circulation and poorly matched vaccine showed an effectiveness of 65% in preventing pneumonia.

The researchers also examined 39 data sets assessing the effects of vaccination among elderly people living in the community. Analyses were divided into five separate comparisons. The first comparison revealed that in elderly people living in the community, inactivated influenza vaccines were not effective for the prevention of influenza, influenza-like illness, or pneumonia. The researchers noted that “well matched vaccines prevented hospital admissions for these illnesses (26%), but not for cardiac disease. Death from respiratory disease was not significantly affected.”

The second comparison assessed the effectiveness of inactivated influenza vaccines in elderly people living in the community who were at risk for complications associated with influenza. Results showed that the only significant effect was that for deaths from all causes (ie, deaths by falls, accidents, poisoning, heart attacks, suicide, etc).

The third comparison evaluated the effectiveness of inactivated influenza vaccines in all healthy elderly people living in the community. This analysis showed that vaccines were effective in preventing hospital admission for influenza or pneumonia (50%) but demonstrated a lack of effect on all-cause mortality.

In the fourth comparison, the researchers assessed the effectiveness of inactivated influenza vaccines in all elderly people living in the community after the adjustment of confounders (eg, sex, age, smoking, comorbidities). They found that “vaccines significantly affected all-cause mortality (47%), and hospital admission for influenza or pneumonia (27%), respiratory diseases (22%), and cardiac disease (24%).”

Finally, the fifth comparison, which evaluated the effectiveness of virosomal influenza vaccines in elderly people living in the community, revealed that vaccines had no effect on all-cause mortality, but when well matched, they prevented influenza-like illnesses and hospital admission during low viral circulation.

LIMITATIONS

Dr. Jefferson noted that one limitation to the study was the lack of data from randomized controlled trials. Of the 64 studies analyzed, 49 were cohort studies, 10 were case-control studies, and only 5 were randomized controlled trials. “Unfortunately, because of the global recommendations on influenza vaccination, placebo-controlled trials, which could clarify the effects of influenza vaccines in individuals, are no longer possible on ethical grounds,” said the researchers.

He attributed the discrepancies in their findings, in part, to the effects of selection bias. It is possible that those people who were vaccinated were most likely to be in better health and, therefore, were most likely to survive, have fewer episodes of pneumonia, etc. Hence, the need for randomized controlled trials—a catch-22, as described by Dr. Jefferson.

DIRECTIVES FOR FUTURE VACCINATION EFFORTS

The researchers said that the modest effectiveness of influenza vaccines in community-dwelling elderly people might be the result of difficulties in achieving good vaccine coverage in those who most need it, or the diluting effect on influenza vaccines of other agents circulating in the community. They commented, “We believe efforts should be concentrated on achieving high vaccination coverage in long-term care facilities coupled with a systematic assessment of the effect of such a policy.”

—Karen L. Spittler

Reference
1. Jefferson T, Rivetti D, Rivetti A, et al. Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review. Lancet. 2005;366:1165-1174.

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