Influenza vaccination reduced the risk for influenza in elderly persons
ACP J Club. 1995 May-June;122:65. doi:10.7326/ACPJC-1995-122-3-065
Govaert TM, Thijs CT, Masurel N, et al. The efficacy of influenza vaccination in elderly individuals. A randomized double-blind placebo-controlled trial. JAMA. 1994 Dec 7;272:1661-5.
To evaluate the efficacy of influenza vaccination in elderly persons.
Randomized, double-blind, placebo-controlled trial with 5-month follow-up (influenza season 1991 to 1992).
15 family practices in the southern region of the Netherlands.
9907 patients aged ≥ 60 years, not known to belong to high-risk groups (patients with heart or lung conditions, diabetes mellitus, chronic renal insufficiency, or chronic staphylococcal infections), in which vaccination had previously been given, were invited. 1838 (19%) agreed to participate, of whom 53% were women and 27% had high-risk conditions.
927 patients were assigned to receive a purified split-virion vaccine containing A/Singapore/6/86(H1N1), A/Beijing/353/89(H3N2), B/Beijing/1/87, and B/Panama/45/90. 911 patients were assigned to receive intramuscular placebo containing a physiologic saline solution.
Main outcome measures
The incidence of clinical and serologic influenza and self-reported influenza.
The incidence of clinical influenza-like illness as diagnosed by a family physician was 1.8% in the vaccine group compared with 3.4% in the placebo group (P = 0.035) (Table). The incidence of serologic influenza was 4.5% in the vaccine group compared with 9.0% in the placebo group (P < 0.001) (Table). After stratification for risk status, sex, age, and previous vaccination status, the incidence of influenza was approximately the same for the various subgroups and the entire trial population. The efficacy of vaccination was highest for a diagnosis of influenza confirmed both clinically and serologically (P = 0.002) (Table). The effect of vaccination was less pronounced for self-reported influenza.
Influenza vaccination reduced the incidence of clinical and serologic influenza in the elderly.
Source of funding: Prevention Fund.
For article reprint: Dr. T.M. Govaert, Mauritsweg 3, NL-6171 RM Stein, the Netherlands. FAX 31-46-4339-099.
Table. Purified split-virion vaccine for influenza vs intramuscular placebo for elderly persons*
|Outcomes at 5 mo||Influenza vaccine||Placebo||RRR (95% CI)||NNT (CI)|
|Clinical influenza||1.8%||3.4%||46% (4 to 70)||64 (33 to 219)|
|Serologic influenza||4.5%||9.0%||50% (28 to 65)||22 (15 to 47)|
|Influenza, confirmed clinically and serologically||1.7%||4.2%||59% (27 to 77)||41 (25 to 111)|
*Abbreviations defined in Glossary; RRR, NNT, and CI calculated from data in article.
A randomized, double-blind, placebo-controlled trial was the piece of scientific evidence missing from the puzzle of influenza vaccine effectiveness in elderly persons. Govaert and colleagues have completed the puzzle and have dispelled the concern raised by Hoskins and colleagues (1) about repeated vaccinations.
Other study designs have shown the effectiveness of influenza vaccine. Case-control studies by Foster and Fedson and colleagues (2, 3) and the Medicare Influenza Vaccine Demonstration Project (MIVDP) (4) showed that influenza vaccine can reduce hospital admissions and hospital deaths from pneumonia and influenza and hospital deaths from all causes by one third to one half during an influenza outbreak. A meta-analysis by Gross and colleagues (5) of the observational studies in elderly persons found that influenza vaccine reduced the risks for pneumonia, hospitalization, and death by one half during an influenza epidemic. Cost-effectiveness studies by Nichol and Mullooly and colleagues (6, 7) confirm that significant cost savings would accrue by vaccinating elderly persons. In addition to being effective, influenza vaccine appears to be safe. In a well-controlled trial, Margolis and colleagues (8) showed that the incidence of side effects was < 5% among male veterans.
Areas not addressed in this study are selection bias (only 19% of those invited participated), documentation of infection by culture, adjustment of follow-up antibody titers by initial antibody titer, and level of protective titer.
Because most deaths from influenza virus infections occur in elderly persons and because influenza vaccine reduces the risk for major morbidity and mortality from influenza by about 50%, influenza vaccine should be given to all persons ≥ 65 years, as recommended by the U.S. Public Health Service.
Peter A. Gross
New Jersey Medical SchoolHackensack, New Jersey, USA
5. Gross PA, Hermogenes A, Sacks HS, Lavandowski RA. The protective efficacy of influenza vaccine in the elderly: a meta-analysis. In: Abstracts of the 34th Interscience Conference on Antimicrobial Agents and Chemotherapy (October 7, 1994; Orlando, FL). Washington, D.C.: American Society for Microbiology; 1994:265 [Abstract 72].
6. Nichol KL, Margolis KL, Wuorenma J, Von Sternberg T. The efficacy and cost effectiveness of vaccination against influenza among elderly persons living in the community. N Engl J Med. 1994;331:778-84.