We documented that maternal immunity against influenza B/Yamagata was conferred to infants within the first 6 months of life.
1162 infants were born to 1140 recruited women: 1092 (94%) infants completed 6 months of follow-up. Proportions of cord blood with HAI antibodies titers ≥40 against A(H1N1), A(H3N2), B/Victoria and B/Yamagata were 31%, 24%, 31% and 54%, respectively. Only 4% of women had maternal influenza vaccination. Cord blood antigen-specific HAI titers ≥40 were found to correlate with protection from infection only for influenza B/Yamagata. No influenza B virus infection occurred in infants ≤60 days of life. Proportional hazards analysis showed that a cord blood HAI titer of 40 was associated with 83% (95% confidence interval: 44%, 95%) reduction in the risk of influenza B/Yamagata infections compared to a cord blood titer <10.
Studies that correlate maternal antibodies with protection from influenza A or B virus infection in young infants in areas with prolonged influenza circulation are lacking.
We conducted a prospective, observational study to evaluate the effects of maternal-transferred antibodies against influenza A and B viruses against laboratory-confirmed influenza in a cohort born over 24 months. Cord blood samples were retrieved at birth and infants were actively followed for the first 6 months of life. Nasal swabs were collected and tested for influenza A and B by RT-PCR whenever an illness episode was identified. Cord blood samples were tested by the hemagglutination inhibition (HAI) assay to viruses that circulated during the follow-up period.
Cowling BJ, Perera RAPM, Fang VJ, Chu DKW, Hui APW, Yeung APC, Peiris JSM, Wong WHS, Chan ELY, Chiu SS. (2019). Maternal antibodies against influenza in cord blood and protection against laboratory-confirmed influenza in infants. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America