The full content of Annals is available to subscribers

Subscribe/Learn More  >
Therapeutics |

Review: Inactivated vaccines provide the greatest protection against influenza in healthy persons

Peter A. Gross, MD
[+] Article, Author, and Disclosure Information

Source of funding: Ministry of Defence, UK.

For correspondence: Dr. V. Demicheli, Servizio Sovrazonale di Epidemiologia, Alessandria, Piemonte, Italy. E-mail epidemi@tin.it.

Ann Intern Med. 2002;136(3):103. doi:10.7326/ACPJC-2002-136-3-103
Text Size: A A A

Question: What is the effectiveness of vaccines in preventing influenza in healthy adults?

Data sources: Studies were identified by searching MEDLINE (1966 to 1997) with the terms influenza, route (oral), route (parenteral), and vaccine; searching EMBASE/Excerpta Medica (1990 to 1997) and the Cochrane Controlled Trials Register; hand searching the journal Vaccine to 1997; scanning the bibliographies of articles; and contacting manufacturers of vaccines and authors of studies in the review.

Study selection: Studies were selected if they were quasirandomized or randomized controlled trials (RCTs) that compared influenza vaccines with placebo, control vaccines, or no intervention or doses or schedules of influenza vaccine in healthy persons 14 to 60 years of age and that assessed protection from exposure to naturally occurring influenza.

Data extraction: Data were extracted on study quality, participant characteristics, intervention, and outcomes. Outcomes included rates of influenza (clinically defined [unspecified], clinically defined on the basis of specific symptoms or signs [specified], and serologically confirmed), hospital admissions, working days lost, and adverse events.

Main results: 20 trials were included (14 RCTs) evaluating 3 types of vaccine: live attenuated aerosol (n = 26 369), inactivated aerosol (n = 1506), and inactivated parenteral (n = 23 628). Live aerosol vaccines were not effective for preventing either type of clinically defined influenza (2 trials). Inactivated vaccines were effective in preventing influenza: Both inactivated aerosol and inactivated parenteral vaccines prevented unspecified clinically defined influenza, and inactivated parenteral vaccines prevented specified clinically defined influenza (Table). Live aerosol and inactivated parenteral vaccines prevented serologically confirmed influenza (Table). No studies of inactivated aerosol reported serologically confirmed influenza. Vaccine and placebo did not differ for working days lost (3 trials), hospitalizations (1 trial), or complications (2 trials). Local tenderness and soreness were increased in patients who received inactivated parenteral vaccine (Table). No increase occurred in systemic myalgia, fever, or fatigue.

Conclusion: Inactivated parenteral vaccines are effective in preventing influenza in healthy adults.

Vaccines vs placebo for preventing influenza in healthy adults at mean 87 days*

OutcomesComparisonsWeighted event ratesNumber of trialsRRR (95% CI)NNT (CI)
CDI unspecifiedIA vs placebo7.2% vs 20%165% (32 to 82)8 (4 to 63)
IP vs placebo17% vs 21%531% (5 to 51)25 (13 to 250)
CDI specifiedIP vs placebo45% vs 53%426% (1 to 45)13 (8 to 29)
SCILA vs placebo0.7% vs 8.5%279% (44 to 92)Not significant
IP vs placebo2.9% vs 8.7%465% (44 to 79)18 (12 to 34)
Local adverse eventsIP vs placebo64% vs 35%4113% (35 to 236)4 (3 to 7)

*CDI = clinically defined influenza; IA = inactivated aerosol vaccine; IP = inactivated parenteral vaccine; LA = live aerosol vaccine; SCI = serologically confirmed influenza. Other abbreviations defined in Glossary; RRR, RRI, NNT, NNH, and CI calculated from data in article using random effects.





Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).


Submit a Comment/Letter
Submit a Comment/Letter

Summary for Patients

Clinical Slide Sets

Terms of Use

The In the Clinic® slide sets are owned and copyrighted by the American College of Physicians (ACP). All text, graphics, trademarks, and other intellectual property incorporated into the slide sets remain the sole and exclusive property of the ACP. The slide sets may be used only by the person who downloads or purchases them and only for the purpose of presenting them during not-for-profit educational activities. Users may incorporate the entire slide set or selected individual slides into their own teaching presentations but may not alter the content of the slides in any way or remove the ACP copyright notice. Users may make print copies for use as hand-outs for the audience the user is personally addressing but may not otherwise reproduce or distribute the slides by any means or media, including but not limited to sending them as e-mail attachments, posting them on Internet or Intranet sites, publishing them in meeting proceedings, or making them available for sale or distribution in any unauthorized form, without the express written permission of the ACP. Unauthorized use of the In the Clinic slide sets will constitute copyright infringement.


Buy Now for $32.00

to gain full access to the content and tools.

Want to Subscribe?

Learn more about subscription options

Related Articles
Related Point of Care
Topic Collections
PubMed Articles
Forgot your password?
Enter your username and email address. We'll send you a reminder to the email address on record.