Vaccination is the best measure to prevent
influenza pandemics. Here, we studied the protective effect against heterologous influenza viruses, including A/reassortant/NYMC X-179A (pH1N1), A/Chicken/Henan/12/2004 (H5N1), A/Chicken/Jiangsu/7/2002 (H9N2) and A/Guizhou/54/89×A/PR/8/34 (A/Guizhou-X) (H3N2), in mice first vaccinated with
a DNA vaccine of haemagglutinin (HA) or
neuraminidase (NA) of A/PR/8/34 (PR8) and then infected with the homologous virus. We showed that PR8 HA or NA vaccination both protected mice against a lethal dose of the homologous virus; PR8 HA or NA
DNA vaccination and then PR8
infection in mice offered poor or excellent protection, respectively, against a second, heterologous influenza virus challenge. In addition, before the second heterologous
influenza infection, the highest antibody level against
nucleoprotein (NP) and matrix (M1 and M2)
proteins was found in the PR8 NA-vaccinated and PR8-infected group. The level of induced cellular immunity against NP and M1 showed a trend consistent with that seen in antibody levels. However, PR8 HA+NA vaccination and then PR8
infection resulted in limited protection against heterologous influenza virus challenge. Results of the present study demonstrated that
infection of the homologous influenza virus in mice already immunized with a NA
vaccine could provide excellent protection against subsequent
infection of a heterologous influenza virus. These findings suggested that NA, a major
antigen of influenza virus, could be an important candidate
antigen for
universal influenza vaccines.