IgG1 and IgG2a titers (×10³) in serum before and after challenge¹.

1Virus specific IgG1 and IgG2a antibody responses were determined and compared among groups before challenge (at week 4 post immunization) and after challenge (at day 4 post challenge). Antibody titers were expressed as the highest dilution having a mean optical density at 450 nm greater than the mean value plus 3 standard deviations of naïve serum samples. 2MN, microneedle vaccine without trehalose; MN+T, microneedle vaccine with trehalose; IM, reconstituted A/PR8 vaccine without trehalose; IM+T, reconstituted A/PR8 vaccine from trehalose-formulated microneedles; Mock, microneedle with trehalose coating buffer only (without A/PR8 vaccine). 3Isotype antibody ratios (IgG2a/IgG1) based on antibody titers before challenge (Week 4) and after challenge (Day4). Before, serum samples (n = 12) collected at week 4 after a single immunization; After, serum samples (n = 6) collected at day 4 after challenge.