Serum neutralising antibody titres against a lineage 2 neuroinvasive West Nile Virus strain in response to vaccination with an inactivated lineage 1 vaccine in a European endemic area.

The research focused on the evaluation of an inactivated Lineage 1 West Nile Virus (WNV) vaccine’s ability to produce serum neutralizing antibodies against a Lineage 2 WNV strain in horses within Europe. The results indicated that the vaccine was effective in generating antibodies against both WNV lineages for up to two years following a booster shot, though in regions where Lineage 2 strains are prevalent, a booster shot is suggested to be administered earlier.

Study Design

• The study was a response to the dramatic increase in West Nile Neuroinvasive Disease (WNND) cases caused by WNV Lineage 2 strains in Hungary and neighboring countries over the past decade, affecting both horses and humans.
• Within this study, 32 seronegative horses were split into two groups: 22 in the vaccination group and 10 in the control group, which remained unvaccinated.
• Horses vaccinated received two initial doses of the Equip® WNV vaccinated (Lineage 1) 28 days apart, roughly 5 months prior to the WNV outbreak season. A booster shot was given a year later.
• Blood samples were collected over a two-year duration from all horses, monitoring for the production of serum neutralizing antibodies that could combat both lineage 1 and lineage 2 of the WNV strain.

Key Findings

• Post-primary vaccination, the antibody titres for both Lineage 1 and 2 in the vaccinated group of horses were significantly higher than those of the control group. The only exception was found at a 6-month mark after primary vaccination for Lineage 2 WNV.
• The antibody titres were notably higher against Lineage 1 than Lineage 2 in all instances.
• Although vaccination with the inactivated Lineage 1 vaccine triggers antibodies against both WNV lineages for up to two years post-booster vaccination, earlier booster shots are recommended in regions where Lineage 2 strain outbreaks are seasonal.
• The study concluded that timing and frequency of booster vaccinations must be appropriate to maintain the highest antibody titres during outbreak seasons, consequently providing optimal protection.

Implications and Recommendations

• In parts of Europe where Lineage 2 WNV outbreaks are seasonal, a more frequent booster vaccination schedule should be implemented for optimal protection against the disease.
• This study suggests that the Equip® WNV vaccine does have cross-protection abilities against different lineages of WNV, but the antibody response against Lineage 2 is slightly less pronounced. Understanding and working on this distinction can further improve the effectiveness of vaccination strategies.
• Further research is necessary to identify the underlying reasons for the lower antibody response against Lineage 2 WNV post-vaccination.