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Direct and Indirect Influenza Vaccine Effects

Direct and Indirect Influenza Vaccine Effects. Adults aged 18-49 years. Objectives. Direct vaccine effects Cochrane Review Indirect vaccine effects Potter, Carman Identify gaps in knowledge Suggest needed research.

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Direct and Indirect Influenza Vaccine Effects

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  1. Direct and Indirect Influenza Vaccine Effects Adults aged 18-49 years

  2. Objectives • Direct vaccine effects • Cochrane Review • Indirect vaccine effects • Potter, Carman • Identify gaps in knowledge • Suggest needed research

  3. Cochrane Review (May 2004)Vaccines for preventing influenza in healthy adults Demicheli, V; Rivetti, D; Deeks, JJ; Jefferson, TO • Studies published 1966-2003 • Adults aged 14-60 years • 25 controlled studies, good quality: • allocation concealment adequate (16), inadequate (7), unclear (2) • properly randomized (20), quasi random(4), not reported (1) • assessment double blinded (19), single blinded (2), not mentioned (4)

  4. Definition of Terms • Relative Risk (RR) • Incidence in vaccinated/incidence in controls • Vaccine Efficacy (VE) = 1-RR x 100% • Risk Difference (RD) • Incidence in controls – incidence in vaccinated • Best measure for estimating decrease in disease burden • Best measure when using non-specific case definition

  5. Inactivated Vaccinevs placebo

  6. Inactivated Vaccinevs placebo or other vaccine

  7. WHO recommended vaccinesplacebo controlled trials • VE clinical definition • 22% (95% CI 14% to 30%) overall • 15% (95% CI 8% to 21%) live aerosol • 25% (95% CI 13% to 35%) inactivated parenteral • 40% (95% CI 13% to 59%) inactivated aerosol • Lab confirmed • 48% (95% CI 24% to 64%) live aerosol • 70% (95% CI 56% to 80%) inactivated parenteral • RD • 6% (95% CI 4% to 8%) overall • 3% live aerosol NS • 7% inactivated parenteral • 9% inactivated aerosol • Work days lost • 0.16 days (95% CI 0.04 to 0.29) all trials • 0.12 days (95% CI 0.00 to 0.24) placebo controlled trials

  8. Cochrane perspective • Vaccinating healthy adults reduced • flu-like illness by only a quarter, • the number of working days lost by less than half a day • Vaccination had no reported relevant adverse effects

  9. A different perspective: direct effects • 20%-30% efficacy clinical disease • 70% efficacy serologically confirmed • Decrease in clinical disease 7% • Missed days from work • 0.12-0.16 days/vaccinee = 2 days per illness • NNT • Vaccinate 14 healthy adults, prevent 1 flu illness associated with average 2 missed work days

  10. Take home message • If one uses a nonspecific definition, appropriate outcome measure should be risk difference, not relative risk or vaccine efficacy • Need large numbers when using non-specific definition

  11. Indirect effects Vaccination health care workers (HCWs)

  12. Vaccination of HCWs #1 Potter et al JID 1997 • 12 LTC facilities, 1059 patients • 4 groups • 6 homes high (>80%) patient vaccination • 6 homes low (<1%) patient vaccination • 3 in each strata randomized to staff vaccination • 1078 HCWs, 61% vaccinated

  13. Outcomes during 5 monthsOctober thru March Vaccination:

  14. Caveats • No analysis by unit of randomization • Serology in 225 unvaccinated pts • 2% flu A, 3% flu B no difference between homes with/without staff vax • Nasopharyngeal aspirates within 48 hrs of symptoms in 212 patients • IFA: 0 influenza, 14 RSV, 11 adeno

  15. Vaccination of HCWs #2Carman et al Lancet 2000 • 20 long term care facilities • Random allocation • 10 offered HCWs vax: 50% vaccinated • 10 no offer: 5% vaccinated

  16. Randomization: HCW vaccination

  17. % mortality vs % HCW vax

  18. % mortality vs % pt vax

  19. Odds ratio for impact of HCW vax on mortality

  20. PCR for flu

  21. Summary: indirect effects • Immunization of HCWs may protect frail institutionalized elderly from influenza-associated deaths • Protection seen with 50%-60% coverage of HCWs

  22. Gaps in knowledgehealthy adults • Direct effects well established • Need to emphasize absolute risk reduction • Expected absolute risk reduction 5%-10% • Indirect effects –significant gaps • Protection of infants or other vulnerable populations by family vaccination • Protection of hospitalized patients • Optimal levels of vaccination to achieve “herd immunity”

  23. Research: healthy adults, indirect effects • Randomized clusters • Nursing homes • Families • Hospitals • Need to achieve • high vaccination rates • sensitive surveillance methods, particularly in elderly • very large populations

  24. Research priorities other age groups • Immunization of school children • High individual benefit • Potentially high population benefit • Study design • Clustered randomization by population units of at least 100,000 each • Outcomes • School absenteeism • Flu hospitalizations powered for aged <6 months and 65+ years (mixed active and passive surveillance to detect)

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