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Impact of Influenza Vaccination during Pregnancy on Maternal Influenza Disease Severity in Rural Nepal
Collrane Frivold1,2, Joanne Katz3, Tsering Pema Lama3,4
1Department of Medicine, University of Washington, Seattle, Washington.
Although maternal influenza vaccination can prevent influenza morbidity and mortality, data are limited on vaccine efficacy/effectiveness against severe disease in low- and middle-income countries (LMICs) at the community level. We evaluated the impact of maternal influenza vaccination on maternal influenza disease severity across seasons in a rural subtropical area in South Asia by analyzing data from a vaccine clinical trial conducted between 2011 and 2014 in Sarlahi District, Nepal. Participants were randomized 1:1 to trivalent seasonal influenza vaccine or saline placebo and followed through 180 days postpartum. Weekly household-based active respiratory surveillance was conducted; if participants reported fever and respiratory symptoms, a midnasal swab was collected and tested for influenza using reverse transcription polymerase chain reaction. Among 3,693 participants (n = 1,847 vaccine; n = 1,846 placebo), we detected 75 influenza illness episodes, including 40 with care seeking and 22 with fever for more than 3 days. Using proportional hazards regression, maternal influenza vaccination reduced the estimated hazard of influenza-associated care-seeking visits and fever for more than 3 days by 36% and 21%, respectively, compared with placebo; however, these differences were not statistically significant. The estimated numbers needed to vaccinate to prevent one influenza illness with care seeking and fever for more than 3 days were 224 and 785, respectively, at 270 days postvaccination. These findings suggest that maternal immunization may reduce the risk of moderate influenza illness among pregnant/postpartum individuals in LMICs, particularly in rural areas where access to care is limited.
Although maternal influenza vaccination can prevent influenza morbidity and mortality, data are limited on vaccine efficacy/effectiveness against severe disease in low- and middle-income countries (LMICs) at the community level. We evaluated the impact of maternal influenza vaccination on maternal influenza disease severity across seasons in a rural subtropical area in South Asia by analyzing data from a vaccine clinical trial conducted between 2011 and 2014 in Sarlahi District, Nepal. Participants were randomized 1:1 to trivalent seasonal influenza vaccine or saline placebo and followed through 180 days postpartum. Weekly household-based active respiratory surveillance was conducted; if participants reported fever and respiratory symptoms, a midnasal swab was collected and tested for influenza using reverse transcription polymerase chain reaction. Among 3,693 participants (n = 1,847 vaccine; n = 1,846 placebo), we detected 75 influenza illness episodes, including 40 with care seeking and 22 with fever for more than 3 days. Using proportional hazards regression, maternal influenza vaccination reduced the estimated hazard of influenza-associated care-seeking visits and fever for more than 3 days by 36% and 21%, respectively, compared with placebo; however, these differences were not statistically significant. The estimated numbers needed to vaccinate to prevent one influenza illness with care seeking and fever for more than 3 days were 224 and 785, respectively, at 270 days postvaccination. These findings suggest that maternal immunization may reduce the risk of moderate influenza illness among pregnant/postpartum individuals in LMICs, particularly in rural areas where access to care is limited.
