Safety and immunogenicity of an inactivated eastern equine encephalitis virus vaccine.

BACKGROUND: Eastern equine encephalitis virus (EEEV) is a mosquito borne alphavirus spread primarily in Atlantic and Gulf Coast regions of the United States. EEEV is the causative agent of a devastating meningoencephalitis syndrome, with approximately 30% mortality and significant morbidity. There is no licensed human vaccine against EEEV. An inactivated EEEV vaccine has been offered under investigational new drug (IND) protocols at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) since 1976. METHODS: Healthy at-risk laboratory personnel received inactivated PE-6 strain EEEV (TSI-GSD 104) vaccine under two separate IND protocols. Protocol FY 99-11 (2002-2008) had a primary series consisting of doses on day 0, 7, and 28. Protocol FY 06-31 (2008-2016) utilized a primary series with doses on day 0 and 28, and month 6. Participants with an inadequate immune response, plaque reduction neutralization test with 80% cut-off (PRNT80) titer < 40, received booster vaccination. Volunteers with prior EEEV vaccination were eligible to enroll for booster doses based on annual titer evaluation. RESULTS: The FY06-31 dosing schema resulted in significantly greater post-primary series immune response (PRNT80 ≥ 40) rates (84% vs 54%) and geometric mean titers (184.1 vs 39.4). The FY 06-31 dosing schema also resulted in significantly greater cumulative annual immune response rates from 1 to up to 7 years post vaccination (75% vs 59%) and geometric mean of titers (60.1 vs 43.0). The majority of probably or definitely related adverse events were mild and local; there were no probably or definitely related serious adverse events. CONCLUSIONS: Inactivated PE-6 EEEV vaccine is safe and immunogenic in at-risk laboratory personnel. A prolonged primary series, with month 6 dose, significantly improved vaccine immunogenicity both post-primary series and longitudinally on annual titers. Despite decades of safe use under IND, full licensure is not planned due to manufacturing constraints, and ongoing development of alternatives.

The Western Equine Encephalitis Lyophilized, Inactivated Vaccine: An Update on Safety and Immunogenicity.

Background: Western Equine Encephalitis (WEE) is a naturally acquired infection and potentially devastating bioweapon, with no specific human countermeasures. An experimental inactivated Western Equine Encephalitis Vaccine (WEEV; WEE TSI-GSD 210) has been used under an IND (investigational New Drug) protocol at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) since 1976. Methods: Over 24 years from 1987 to 2011, 876 subjects received 3 primary vaccine doses under 3 studies with 1,537 booster doses administered (FY87-8, phase 2, laboratory workers, vaccine lots 1-81-1, 1-81-2, and 2-1-91; FY99-12, phase 2 laboratory workers, lot 2-1-91; and FY09-02, phase 1 healthy volunteer, lot 3-1-92). Post-vaccination safety and immunogenicity [plaque reduction neutralization test 80% (PRNT80) > 1:40] were analyzed. Results: Overall PRNT80 response to the primary series in FY87-8 was 42% (326/770) but dropped to 16% (14/87) in FY99-12, prompting study FY09-02, which achieved 89% (17/19). The first booster response rate was 68% (814/1194) in FY87-8, 53% (171/324) in FY99-12, and 100% (10/10) in FY09-02. The majority of definitely related adverse reactions (AEs) were mild and local with no definitely related serious AEs. No laboratory acquired WEE infection was documented during this period despite 4 reported exposures in vaccinated subjects. Conclusion: The TSI-GSD 210 WEE vaccine was immunogenic, safe and well tolerated. Use of this vaccine could be considered in an emergency setting. Despite decades of safe and effective use under IND, full licensure is not planned due to manufacturing constraints, and a strategic decision to develop alternatives. Clinical Trial Registration: https://clinicaltrials.gov/, identifier NCT01159561.