According to research in the journal Vaccine, both live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV) are safe for nursing mothers; however, breast milk and serum antibody responses were higher for IIV and one possible transmission of LAIV virus to an infant was observed.
A randomized, double-blind study was performed during the flu seasons of 2011 to 2012 and 2012 to 2013 to compare immunogenicity of LAIV to IIV as well as vaccine safety for both mother and infant. A total of 248 mothers and 249 corresponding infants were enrolled. Mothers received LAIV plus intramuscular placebo or IIV plus intranasal placebo. Notably, no women were enrolled in both seasons. Breast milk and serum antibody responses, measured at day 0 and 28, showed breast milk immunoglobulin (Ig) G, breast milk IgA (H1N1 only), serum hemagglutination inhibition (HAI), and serum IgG responses were significantly higher following administration of IIV compared with LAIV.
Milk and nasal swabs collected on day 0, 2, and 8 to detect transmission of LAIV to infants found that 1 mother who received LAIV transmitted vaccine virus to the infant, who remained healthy. No virus was detected in breast milk. Investigators found that breast milk IgA to H1N1 was higher in IIV recipients compared with LAIV recipients (P =.003), and IgG titers were higher for all 5 strains over both influenza seasons (P ≤.0002).
This investigation had several limitations. First, comparisons between the 2 influenza seasons investigated here are difficult, and the seasonal vaccines shared only the H1N1 antigen in common. Two seasons were, however, necessary to meet the enrollment goal determined in sample size calculations. Second, only serum and breast milk antibody response were assessed. These HAI antibodies induced by IIVs are known to be a good surrogate correlate of protection, but mechanisms of immunity for LAIV are less well understood and may include nasal IgA responses and antigen-specific cytokine-secreting T cells. Third, vaccine effectiveness was not followed up on throughout the influenza season and the relative effectiveness of LAIV and IIV during the specific study season is pertinent to any conclusion preferring IIV over LAIV.
Investigators conclude that, as the Advisory Committee on Immunization Practices has recommended the use of any licensed, age-appropriate influenza vaccine for the 2018 and 2019 flu season, “LAIV will be an option for healthy breastfeeding women and the findings of this study may be applicable.”
Brady RC, Jackson LA, Frey SE, et al. Randomized trial comparing the safety and antibody responses to live attenuated versus inactivated influenza vaccine when administered to breastfeeding women. Vaccine. 2018;36:4663-4671.