Fig. 1.

Maternal antibodies mediate protection against lethal influenza challenge. a Design; Adult female mice were vaccinated either 1× or 2× with Inflexal, or 3× with PBS before and/or after mating. Blood samples of offspring were collected weekly from the age of 1 day. Number of pups varies due to available litter size. b Level and duration of detectable maternal antibodies; ELISA titers against homologous H1 A/California/07/09 in dams and offspring. Pups were weaned at age 3 weeks. Maternal antibodies are present longer and at higher titers when mothers received a prime / boost vaccination with Inflexal. c Comparison of protection mediated by maternal antibodies; Adult female mice were vaccinated either 1× or 2× with Inflexal or PBS before and/or during mating. Offspring was challenged with H1N1 A/Netherlands/602/09 at the age of 7 weeks. As challenge controls mice received either PBS or broadly protective monoclonal antibody CR6261 intramuscularly 1 day prior to challenge. One day prior to challenge, at age 7 weeks, blood samples were taken and analyzed for recHA A/California/07/09 binding antibodies in an IgG ELISA assay and H1N1 A/California/07/09 HAI titers. Samples from pups of the mothers which were immunized twice were also tested for H1N1 A/California/07/09 MNA titers in a pseudoparticle assay. An increase in survival was observed when protective maternal antibodies were present in the offspring before challenge as detected by homologous HA ELISA and confirmed by MNA, but in absence of HAI titers. *** p < 0.001