Clinical and immunological response to attenuated tissue-cultured smallpox vaccine LC16m8.

CONTEXT: The attenuated, tissue-cultured, third-generation smallpox vaccine LC16m8 was administered to vaccinia-naive infants in Japan during the 1970s without serious adverse events. It is a good candidate for use as part of a prevention plan for bioterrorism.

OBJECTIVE: To assess the immunogenicity and frequency of adverse events of LC16m8 vaccine in unvaccinated and previously vaccinated adults.

DESIGN, SETTING, AND PARTICIPANTS: Between 2002 and 2005 we vaccinated and revaccinated 1529 and 1692 adults, respectively, in the Japan Self-Defense Forces with LC16m8 vaccine, given intraepidermally using a bifurcated needle. Vaccinees were examined 10 to 14 days after vaccination to determine if they had developed a major skin reaction ("take"). Neutralizing antibody responses among 200 participants were assessed using a plaque-reduction neutralization test 30 days postvaccination. We monitored vaccinees for adverse events for 30 days postvaccination.

MAIN OUTCOME MEASURES: Documentation of a vaccine take, presence of neutralizing antibody response, and frequency of adverse events.

RESULTS: The proportions of take in vaccinia-naive and previously vaccinated individuals were 1443 of 1529 (94.4% [95% confidence interval {CI}, 93.2%-95.9%] and 1465 of 1692 (86.6% [95% CI, 85.0%-88.2%]), respectively. Seroconversion or an effective booster response among the individuals with take was elicited in 37 of 41 (90.2% [95% CI, 81.2%-99.3%]) vaccinia-naive participants and in 93 of 155 (60.0% [95% CI, 52.3%-67.7%]) previously vaccinated participants. One case of allergic dermatitis and another of erythema multiforme, both of which were mild and self-limited, were suspected to be caused by vaccination. No severe adverse events were observed.

CONCLUSION: Administration of an attenuated tissue-cultured smallpox vaccine (LC16m8) to healthy adults was associated with high levels of vaccine take and seroconversion in those who were vaccinia-naive and yielded an effective booster response in some previously vaccinated individuals.