Nancy (onset of labour, mode of delivery,gestational age at delivery) and perinatal outcomes (birth weight, Apgar score, and transfer to neonatal care unit) between women who received A/H1N1 2009 influenza vaccine and women non-vaccinated (Table 3). Determinants of non vaccination were studied in the 1326631 cohort and previously published [20]. In a multivariate logistic regression, immigrant women and those having a low socio-economic status were independent factors of non vaccination. We compared pregnancy and perinatal outcomes in vaccinated and non vaccinated women according to different categories of “immigrant women” and “socio-economic status”. No significant differences were evidenced between the two groups (data not shown).No difference on pregnancy and perinatal outcomes was evidenced between vaccinated women, non-vaccinated women without seroconversion, and women with virologically confirmed influenza or who seroconverted without vaccination, and between women who received oseltamivir and those who did not receive oseltamivir (data not shown).424 (48.3) 312 (35.6) 141 (16.1) 467 (53.2) 87 (9.9) 88 (10.0) 401 (45.7) 131 (14.9) 415 (47.3)507 (57.8) 203 (23.1) 167 (19.0)confirmed A/H1N1 influenza received oseltamivir and delivery occurred at term without complication for mother and infant. The two other women did not receive oseltamivir and delivered at term without complication for mother and infant. A total of 55 women reported ILI, among whom only 3 benefited of an additional visit at the maternity, and 72 women reported contact with a H1N1 case, among whom 24 had a nasal swab with negative ML 281 result. A total of 39 women (including the woman previously mentioned with positive PCR) (4.5 ) received oseltamivir without additional visit or PCR (20 for ILI, and 19 for preventive reasons), including 25 (64.1 ) women who were not vaccinated against A/ H1N1 2009 influenza. None of the 877 women was hospitalized for influenza.DiscussionIn this cohort of pregnant women conducted 113-79-1 web during the H1N1 2009 pandemic, the number of laboratory-documented influenza infections remained low despite low vaccine coverage (36.5 ): only one woman had PCR-confirmed A/H1N1 influenza and 10 non-vaccinated women seroconverted between inclusion and delivery; no serious case of influenza and no hospitalization for influenza were reported. Of note, the low level of influenza infection (rate of 2.6 per 100 pregnant women) is reliable since both PCR and serological data were combined for diagnosis. It could be suggested that the low rate of influenza infection in our cohort was related to the willingness of women to participate to the study with a selection of women understanding preventive measures to avoid flu infection. However, vaccination rate (36.5 ), although rather low, was close to the coverage rate in generalPandemic Influenza 2009 Vaccine and PregnancyTable 2. Humoral immunity against pandemic A/H1N1 2009 influenza in vaccinated and non-vaccinated pregnant women at baseline and delivery (n = 678).2009 A/H1N1 influenza vaccinated pregnant women N = 256 At inclusion Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] At delivery Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] Seroconversion rate1, 12926553 Number ( ) of women [95 CI] 49.8 [43.0?7.7] 179 (69.9) [63.9?5.5] 171 (66.8) [60.1?2.5] 7.3 [6.7?.0] 13 (5.1) [2.7?.5]Non-vaccinated pregnant women N =6.7 [6.3?.1] 19 (4.5) [2.7?.0]7.3 [6.8?.8] 26 (6.2) [.Nancy (onset of labour, mode of delivery,gestational age at delivery) and perinatal outcomes (birth weight, Apgar score, and transfer to neonatal care unit) between women who received A/H1N1 2009 influenza vaccine and women non-vaccinated (Table 3). Determinants of non vaccination were studied in the 1326631 cohort and previously published [20]. In a multivariate logistic regression, immigrant women and those having a low socio-economic status were independent factors of non vaccination. We compared pregnancy and perinatal outcomes in vaccinated and non vaccinated women according to different categories of “immigrant women” and “socio-economic status”. No significant differences were evidenced between the two groups (data not shown).No difference on pregnancy and perinatal outcomes was evidenced between vaccinated women, non-vaccinated women without seroconversion, and women with virologically confirmed influenza or who seroconverted without vaccination, and between women who received oseltamivir and those who did not receive oseltamivir (data not shown).424 (48.3) 312 (35.6) 141 (16.1) 467 (53.2) 87 (9.9) 88 (10.0) 401 (45.7) 131 (14.9) 415 (47.3)507 (57.8) 203 (23.1) 167 (19.0)confirmed A/H1N1 influenza received oseltamivir and delivery occurred at term without complication for mother and infant. The two other women did not receive oseltamivir and delivered at term without complication for mother and infant. A total of 55 women reported ILI, among whom only 3 benefited of an additional visit at the maternity, and 72 women reported contact with a H1N1 case, among whom 24 had a nasal swab with negative result. A total of 39 women (including the woman previously mentioned with positive PCR) (4.5 ) received oseltamivir without additional visit or PCR (20 for ILI, and 19 for preventive reasons), including 25 (64.1 ) women who were not vaccinated against A/ H1N1 2009 influenza. None of the 877 women was hospitalized for influenza.DiscussionIn this cohort of pregnant women conducted during the H1N1 2009 pandemic, the number of laboratory-documented influenza infections remained low despite low vaccine coverage (36.5 ): only one woman had PCR-confirmed A/H1N1 influenza and 10 non-vaccinated women seroconverted between inclusion and delivery; no serious case of influenza and no hospitalization for influenza were reported. Of note, the low level of influenza infection (rate of 2.6 per 100 pregnant women) is reliable since both PCR and serological data were combined for diagnosis. It could be suggested that the low rate of influenza infection in our cohort was related to the willingness of women to participate to the study with a selection of women understanding preventive measures to avoid flu infection. However, vaccination rate (36.5 ), although rather low, was close to the coverage rate in generalPandemic Influenza 2009 Vaccine and PregnancyTable 2. Humoral immunity against pandemic A/H1N1 2009 influenza in vaccinated and non-vaccinated pregnant women at baseline and delivery (n = 678).2009 A/H1N1 influenza vaccinated pregnant women N = 256 At inclusion Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] At delivery Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] Seroconversion rate1, 12926553 Number ( ) of women [95 CI] 49.8 [43.0?7.7] 179 (69.9) [63.9?5.5] 171 (66.8) [60.1?2.5] 7.3 [6.7?.0] 13 (5.1) [2.7?.5]Non-vaccinated pregnant women N =6.7 [6.3?.1] 19 (4.5) [2.7?.0]7.3 [6.8?.8] 26 (6.2) [.