Seasonal Influenza Vaccine and Protection against Pandemic (H1N1) 2009-Associated Illness among US Military Personnel

Abstract

IntroductionA novel A/H1N1 virus is the cause of the present influenza pandemic; vaccination is a key countermeasure, however, few data assessing prior seasonal vaccine effectiveness (VE) against the pandemic strain of H1N1 (pH1N1) virus are available.Materials and MethodsSurveillance of influenza-related medical encounter data of active duty military service members stationed in the United States during the period of April–October 2009 with comparison of pH1N1-confirmed cases and location and date-matched controls. Crude odds ratios (OR) and VE estimates for immunized versus non-immunized were calculated as well as adjusted OR (AOR) controlling for sex, age group, and history of prior influenza vaccination. Separate stratified VE analyses by vaccine type (trivalent inactivated [TIV] or live attenuated [LAIV]), age groups and hospitalization status were also performed. For the period of April 20 to October 15, 2009, a total of 1,205 cases of pH1N1-confirmed cases were reported, 966 (80%) among males and over one-half (58%) under 25 years of age. Overall VE for service members was found to be 45% (95% CI, 33 to 55%). Immunization with prior season's TIV (VE = 44%, 95% CI, 32 to 54%) as well as LAIV (VE = 24%, 95% CI, 6 to 38%) were both found to be associated with protection. Of significance, VE against a severe disease outcome was higher (VE = 62%, 95% CI, 14 to 84%) than against milder outcomes (VE = 42%, 95% CI, 29 to 53%).ConclusionA moderate association with protection against clinically apparent, laboratory-confirmed Pandemic (H1N1) 2009-associated illness was found for immunization with either TIV or LAIV 2008–09 seasonal influenza vaccines. This association with protection was found to be especially apparent for severe disease as compared to milder outcome, as well as in the youngest and older populations. Prior vaccination with seasonal influenza vaccines in 2004–08 was also independently associated with protection.

Pre-Existing Cross-Reactive Antibodies to Avian Influenza H5N1 and 2009 Pandemic H1N1 in US Military Personnel

“…Vaccine effectiveness (VE) was high in persons 40 (55%) or 25 (50%) years of age but very low in persons 25-39 years of age ( 10%). 7 These findings correlate with the high levels of cross-reactive 2009 pH1N1 antibodies reported here, with 30% in the 1960-1965 cohort (age range = 35-48) but only 4% in the 1972-1977 cohort (age range = 23-36). Our findings are similar to the results found recently in an elderly population in the United States.…”

Pandemic influenza A(H1N1)pdm09: risk of infection in primary healthcare workers

“…infection with influenza A(H1N1)pdm09 is uncertain, and a range of estimates have been made, which range from indicating protection, [10][11][12][13] to no effect, [14][15][16][17][18][19][20][21][22][23] to increased susceptibility. [24][25][26] A recent meta-analysis found that prior receipt of seasonal influenza vaccination may have been associated with moderate protection against influenza A(H1N1)pdm09.…”

“…38 However, the observational design of the Canadian study, like the present one, means that the association may be due to confounding or bias. 39 A protective effect of seasonal vaccination against influenza A(H1N1)pdm09 infection has been demonstrated in observational studies from Mexico, Argentina, and the US; [10][11][12][13] while other observational studies, 15,16,40 and a randomised controlled trial, 14 have shown no association. A 2012 meta-analysis including 13 studies found no association, but when studies judged to have a moderate or high risk of bias were excluded from the analysis (leaving eight studies), a protective effect on laboratoryconfirmed infection was observed.…”

T Cell-Mediated Protection against Lethal 2009 Pandemic H1N1 Influenza Virus Infection in a Mouse Model

“…The NC/99 virus was continuously used in seasonal influenza vaccines for several years. Recent reports of surveillance data indicated that at least partial levels of protection against the recent pandemic H1N1 virus are associated with prior vaccination with seasonal influenza vaccines (16,25). Since in our hands there was no observed neutralization activity or protection by sera from NC/99-primed mice against CA/E3/09 virus, we speculate that the general population having previously received seasonal influenza vaccines containing NC/99 virus could possibly harbor some level of T-cell immunity that might help to reduce disease severity during 2009 pandemic influenza infection.…”