Herd immunity without evidence of viral circulation during seven years of vaccination with Porvac®, a subunit vaccine against classical swine fever.

Subunit vaccines against classical swine fever (CSF) have been proposed as a safer alternative to modified live vaccines. Porvac®, based on the chimeric protein E2-CD154 (fusion of CSFV E2 glycoprotein and CD154), was registered in Cuba in 2017. This study reports seven years of Porvac® use in the Isle of Youth. In November 2017, all 30,000 domestic pigs were immunized twice within six weeks. Thereafter, piglets were vaccinated at 2-3 weeks of age and breeding stock twice annually. Serological monitoring showed a sharp rise in anti-E2 antibodies, from 43.5% before vaccination to 97.6% at six months post-vaccination (mpv). The fraction of animals with protective neutralizing antibody titres increased from 24% at baseline to 88.4% at six mpv and remained close to 90% throughout the study. A steady decline in anti-Erns antibody prevalence was observed, and viral RNA was undetectable in 200 sera analysed at 0 and 60 mpv. Importantly, no CSF outbreaks have been reported since 2018. The sustained population immunity; reduced Erns seropositivity, and absence of viral circulation strongly suggest that Porvac® has contributed to effective CSF control in this region.