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N Engl J Med. 2014 Sep 4;371(10):918-31. doi: 10.1056/NEJMoa1401480.

Influenza vaccination of pregnant women and protection of their infants.

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From the Medical Research Council, Respiratory and Meningeal Pathogens Research Unit (S.A.M., C.L.C., L.K., A.H., S.J., P.V.A., N.N., K.P.K., M.C.N.), the Department of Science and Technology-National Research Foundation, Vaccine-Preventable Diseases (S.A.M., C.L.C., L.K., A.H., S.J., P.V.A., N.N., M.C.N.), and the Perinatal HIV Research Unit (A.V.), University of the Witwatersrand, the National Institute for Communicable Diseases, the National Health Laboratory Service, Centre for Vaccines and Immunology (S.A.M., F.T., M.V.), Johannesburg, and the Department of Medical Virology, University of Pretoria, Pretoria (M.V.) - all in South Africa; the School of Medicine and Children's Hospital, University of Colorado (A.W.), the Department of Pediatrics, Medicine and Pathology, University of Colorado School of Medicine (E.A.F.S.), and the Center for Global Health, Department of Epidemiology, Colorado School of Public Health (E.A.F.S.) - all in Aurora, Colorado; the Department of Medicine and Department of Global Health, University of Washington (J.R.O.), and the Vaccine Access and Delivery Global Program, PATH (J.R.O., K.M.N.) - both in Seattle; and the Hubert Department of Global Health, Rollins School of Public Health, and the Division of Infectious Diseases, School of Medicine, Emory University, Atlanta (K.P.K.).



There are limited data on the efficacy of vaccination against confirmed influenza in pregnant women with and those without human immunodeficiency virus (HIV) infection and protection of their infants.


We conducted two double-blind, randomized, placebo-controlled trials of trivalent inactivated influenza vaccine (IIV3) in South Africa during 2011 in pregnant women infected with HIV and during 2011 and 2012 in pregnant women who were not infected. The immunogenicity, safety, and efficacy of IIV3 in pregnant women and their infants were evaluated until 24 weeks after birth. Immune responses were measured with a hemagglutination inhibition (HAI) assay, and influenza was diagnosed by means of reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assays of respiratory samples.


The study cohorts included 2116 pregnant women who were not infected with HIV and 194 pregnant women who were infected with HIV. At 1 month after vaccination, seroconversion rates and the proportion of participants with HAI titers of 1:40 or more were higher among IIV3 recipients than among placebo recipients in both cohorts. Newborns of IIV3 recipients also had higher HAI titers than newborns of placebo recipients. The attack rate for RT-PCR-confirmed influenza among both HIV-uninfected placebo recipients and their infants was 3.6%. The attack rates among HIV-uninfected IIV3 recipients and their infants were 1.8% and 1.9%, respectively, and the respective vaccine-efficacy rates were 50.4% (95% confidence interval [CI], 14.5 to 71.2) and 48.8% (95% CI, 11.6 to 70.4). Among HIV-infected women, the attack rate for placebo recipients was 17.0% and the rate for IIV3 recipients was 7.0%; the vaccine-efficacy rate for these IIV3 recipients was 57.7% (95% CI, 0.2 to 82.1).


Influenza vaccine was immunogenic in HIV-uninfected and HIV-infected pregnant women and provided partial protection against confirmed influenza in both groups of women and in infants who were not exposed to HIV. (Funded by the Bill and Melinda Gates Foundation and others; numbers, NCT01306669 and NCT01306682.).

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