Clinical and Immunological Response to Attenuated Tissue-Cultured Smallpox Vaccine LC16m8

Abstract

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. To assess the immunogenicity and frequency of adverse events of LC16m8 vaccine in unvaccinated and previously vaccinated adults. 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. Documentation of a vaccine take, presence of neutralizing antibody response, and frequency of adverse events. 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. 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.