Influenza 2014-2015 among pregnant Japanese women: primiparous vs multiparous women.

This study was performed to determine whether multiparous pregnant women are prone to influenza. A questionnaire survey was conducted at 19 centres located throughout Japan, targeting all 6,694 postpartum women within 7 days after birth before leaving the hospital. All women gave birth during the study period between March 1, 2015, and July 31, 2015. Data regarding vaccination and influenza infection in or after October 2014, age, previous experience of childbirth, and number and ages of cohabitants were collected. Seventy-eight percent (n = 51,97) of women given questionnaires responded. Of these, 2,661 (51 %) and 364 (7.0 %) women reported having been vaccinated and having contracted influenza respectively. Multiparous women had a higher risk of influenza regardless of vaccination status (8.9 % [121/1362] vs 5.7 % [74/1299], relative risk [95 % confidence interval], 1.80 [1.36 to 2.38] for vaccinated and 9.3 % [112/1198] vs 4.3 % [57/1328], 2.18 [1.60 to 2.97] for unvaccinated women) compared to primiparous women. The risk of influenza increased with increasing number of cohabitants: 4.8 % (100/2089), 7.5 %, (121/1618), 9.0 %, (71/785), and 10.4 % (58/557) for women with 1, 2, 3, and ≥4 cohabitants respectively. Family size is a risk factor for influenza infection in pregnancy.

Vaccination during the 2013-2014 influenza season in pregnant Japanese women.

This questionnaire survey was conducted at 11 hospitals in Japan to determine vaccination coverage against seasonal influenza and the prevalence rate of influenza among pregnant Japanese women. Of 2,808 postpartum women who gave birth at the 11 hospitals during the study period from March 1, 2014, to July 31, 2014, 1,713 (61 %) participated in this study and 876 (51 %) reported having received vaccination against influenza in or after October 2013. Women aged <25 years had a significantly lower vaccination rate than those aged ≥25 years (31 % vs. 53 %, respectively; p = 0.0000). Eighty-seven (5.1 %) and 1,626 (94.9 %) women did and did not contract influenza, respectively. Although prior birth did not affect overall vaccination coverage (50 % for primiparous vs. 53 % for multiparous), multiparous women had a significantly higher rate of contracting influenza than primiparous women, irrespective of vaccination status (5.6 % vs. 2.2 % [p = 0.0216] and 9.7 % vs. 3.5 % [p = 0.0003] for women with and without vaccination, respectively). The 2013-2014 vaccination program significantly reduced the influenza infection rate by 35 % (3.9 % vs. 6.3 % for women with and without vaccination, respectively; p = 0.0272). Seventy-two (83 %) of the 87 women took antiviral agents for the treatment of influenza and two (2.3 %) required hospitalization. These results suggested that pregnant Japanese women had a high level of concern regarding seasonal influenza. However, campaigns targeting young pregnant Japanese women, as well as multiparous women, for vaccination are needed in order to further reduce the incidence of influenza among pregnant Japanese women.