Protection of weaned pigs by vaccination with human adenovirus 5 recombinant viruses expressing the hemagglutinin and the nucleoprotein of H3N2 swine influenza virus.

Swine influenza virus (SIV), subtype H3N2, is a recent reassortant virus that emerged in 1998 in North American swine causing severe respiratory and reproductive disease. In this study, two replication-defective adenovirus recombinants were developed as potential vaccines against H3N2 influenza viruses. Three groups of 3-week-old pigs (10 pigs per group) were vaccinated intramuscularly (IM) with the recombinants; one group was vaccinated with the recombinant adenovirus expressing the influenza virus H3 hemagglutinin (HA) protein, one group was vaccinated with the recombinant adenovirus expressing the nucleoprotein (NP), and one group was vaccinated with both recombinants in a mixture. Two additional control groups (10 pigs per group) were included in the animal trial. One control group was challenged with a virulent H3N2 field strain and one control group remained unchallenged. The results showed that pigs in the groups given the recombinant adenovirus expressing HA alone and HA plus NP developed high levels of virus-specific hemagglutination-inhibition (HI) antibody by 4 weeks post vaccination. Pigs in the group vaccinated with both recombinant viruses in a mixture were completely protected. Complete protection was shown by the lack of nasal shedding of virus following challenge and by the lack of lung lesions at 1 week following the challenge infection. Thus, replication-incompetent adenovirus vaccines given simultaneously to pigs are efficacious for SIV and have the additional advantage over commercial vaccines that suckling piglets have no pre-existing maternally-derived antibody to block early life vaccination.