A Rift Valley Fever Vaccine Trial. 1. Side Effects and Serologic Response Over a Six-Month Follow-Up
ARMY MEDICAL RESEARCH INST OF INFECTIOUS DISEASES FORT DETRICK MD
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A formalin-inactivated Rift Valley fever vaccine, originally produced in primary monkey kidney cells, has been used to protect laboratory workers. A trial of a modified vaccine, newly formulated in well-characterized diploid fetal rhesus lung cells, was conducted with 114 men aged 19-24 years. Of the 107 subjects who received up to three injections of 0.1 to 1 ml vaccine an additional seven received a placebo one had a local hypersensitivity-type reaction and another a generalized urticarial syndrome. Both cases had a prior history of hypersensitivity states. No pyrogenicity was detected and only insignificant systemic reactions were recorded. Mild and transient local reactions ranged from 5 at the lowest dose level to 43 at the highest. Serologic response, as assessed by plaque reduction neutralizing antibody titers, was dose dependent. Within a single vaccine lot tested at multiple dose levels, peak day 42 geometric mean titers ranged from 48 at 0.1 ml x 3 to 436 at 1.0 ml x 3. Reciprocal titers of or 40 are considered to be protective. Comparison of three lots at the 0.5 ml level indicated between lot variability, though this was not statistically significant. A sharp decline in antibody titers was observed in all vaccination groups by day 84 six months after vaccination apparently protective antibody titers were present only in groups that received 1 ml x 3 and 0.5 ml x 3 of the most antigenic lot of vaccine. These results suggest that 1 the vaccine is generally nonreactogenic, but individuals with a prior history of hypersensitivity states should be observed for allergic side effects 2 existing vaccine supplies cannot be extended by using lower dose levels without a lower and less sustained serologic response 3 a booster dose is necessary six months or more following the primary series 4 although the current TSI-GSD-200 vaccine is immunogenic, a more potent vaccine is needed.
- Medicine and Medical Research