Oral Presentation Abstracts: 25B

[25B]

EFFICACY OF OKA/MERCK VARICELLA VACCINE AFTER CONCOMITANT ADMINISTRATION WITH M-M-R®II

B.J. Kuter (1), H.R. Shinefield (2), S.B. Black (2), S.J.R. Vessey (1), C.Y. Chan (1),
M. Waters (1), J.C. Sadoff (1), J.F. Heyse (3), H. Matthews (3), S. Li (3), I. S.F. Chan (3)
Departments of (1) Vaccine Infectious Disease and (3) Biostatistics, Merck Research Laboratories, West Point, PA, USA. (2) Kaiser Permanente, San Francisco, USA

Objective:
To determine the effect of concomitant administration of M-M-R®II and Oka/Merck varicella vaccine on postvaccination varicella breakthrough infection rates.

Study Design:
Healthy children, 1 to 6 years of age, received Oka/Merck varicella vaccine either concomitantly with (N=299) or six weeks after (N=276) M-M-R®II. Subjects were followed annually for 5 years to obtain information about breakthrough cases of varicella infection. Observed annualized breakthrough rates were compared with expected annualized breakthrough rates in unvaccinated susceptible children to provide an estimate of efficacy for Oka/Merck varicella vaccine.

Results:
The observed annualized varicella breakthrough rate in the group who received the vaccines concomitantly was 1.4% (95% CI: 0.8%, 2.0%) compared with 1.1% (95% CI: 0.6%, 1.7%) for the group who received Oka/Merck varicella vaccine six weeks after M-M-R®II. Comparison with age adjusted expected varicella breakthrough rates yielded an estimated efficacy of 88.9% (95% CI: 83.7%, 93.7%) for Oka/Merck varicella vaccine given concomitantly with M-M-R®II and 90.5% (95% CI: 86.2%, 95.0%) for Oka/Merck varicella vaccine given six weeks after M-M-R® II.

Conclusions:
Oka/Merck varicella vaccine induced long lived protection against varicella infection when used concomitantly with M-M-R®II. The estimated efficacy of Oka/Merck varicella vaccine was unaffected by concomitant administration of
M-M-R®II.

Corresponding Author: Dr. S.J.R. Vessey, Associate Director, Clinical Vaccine Research, Merck & Co., Inc.; Phone: (610) 397-3770, Fax: (610) 397-3371, Email: rupert_vessey@merck.com