Context Additional smallpox vaccine doses are needed to augment current US national
stockpile. Aventis Pasteur smallpox vaccine (APSV), initially manufactured
in the 1950s from the New York Board of Health vaccinia strain in a frozen
preparation, appears as effective as lyophilized vaccine but the effectiveness
of diluted doses of APSV is unclear.
Objective To compare the vaccination success rate and the reaction profile of
various APSV dilutions.
Design, Setting, and Participants A double-blind, randomized controlled trial of 340 healthy vaccinia-naive
adults aged 18 to 32 years from 3 academic medical centers who were vaccinated
with 1 of 3 strengths of APSV dilutions (undiluted, 1:5, and 1:10) between
October 9, 2002, and February 24, 2003. Volunteers were followed up every
3 to 5 days until the vaccination site healed for bandage changes, vaccine
response assessment, and adverse event evaluation, followed by 1- and 2-month
clinic evaluations and 6-month telephone interview.
Main Outcome Measures Successful vaccination, defined by presence of a vesicle or pustule
at the inoculation site 6 to 11 days postvaccination, and local and systemic
reactions to vaccination.
Results A total of 340 volunteers were vaccinated (vaccine dose: undiluted,
n = 113; 1:5 dilution, n = 114; and 1:10 dilution, n = 113). Following vaccination,
99.4% (95% confidence interval [CI], 97.9%-99.9%) of all volunteers had successful
vaccinations. Success rates did not differ between the dilution groups (undiluted,
100.0%; 95% CI, 96.8%-100.0%; 1:5 dilution, 98.2%; 95% CI, 93.8%-99.8%; 1:10
dilution, 100.0% 95% CI, 96.8%-100.0%; P = .33).
Overall, 99.7% of volunteers reported at least 1 local symptom at the vaccination
site, and 61.8% had axillary lymphadenopathy, 15.0% developed satellite lesions,
and 7.6% developed a rash away from the vaccination site. Fever developed
in 21.5%. No differences were noted in local or systemic reactions between
the 3 dilution groups (P>.05 for each comparison).
A total of 25% of volunteers missed scheduled duties due to vaccine-related
Conclusions Even at diluted doses, APSV is an effective smallpox vaccine, allowing
for expansion of the current stockpile. However, reactogenicity was not reduced
with dilution of the vaccine and, as with other smallpox vaccines, may impair