Serological Memory and Long-term Protection to Novel H1N1 Influenza Virus After Skin Vaccination

Background. A major goal in influenza vaccine development is induction of serological memory and cellular responses to confer long-term protection and limit virus spread after infection. Here, we investigate induction of long-lived immunity against the 2009 H1N1 virus after skin vaccination. Methods. BALB/c mice received a single dose of 5 mu g inactivated A/California/04/09 virus via coated metal microneedles (MN) applied to skin or via subcutaneous injection. Results. MN or subcutaneous vaccination elicited similar serum IgG and hemagglutination inhibition titers and 100% protection against lethal viral challenge 6 weeks after vaccination. Six months after vaccination, the subcutaneous group exhibited a 60% decrease in functional antibody titers and extensive lung inflammation after challenge with 10 x LD(50) of homologous virus. In contrast, the MN group maintained high functional antibody titers and IFN-gamma levels, inhibition of viral replication, and no signs of lung inflammation after challenge. MN vaccination conferred complete protection against lethal challenge, whereas subcutaneous vaccination induced only partial protection. These findings were further supported by high numbers of bone marrow plasma cells and spleen antibody-secreting cells detected in the MN group. Conclusions. A single skin vaccination with MN induced potent long-lived immunity and improved protection against the 2009 H1N1 influenza virus, compared with subcutaneous injection.