Partial uptake of varicella vaccine and the epidemiological effect on varicella disease in 11 day-care centers in North Carolina.

BACKGROUND: The increasing use of varicella vaccine in children attending day care has rapidly decreased the incidence of wild-type varicella disease. The herd immunity noted is significant and will have an effect on the epidemiology of natural varicella. OBJECTIVE: To monitor the change in varicella incidence in day-care attendees after the licensure of varicella vaccine. DESIGN: A prospective observational cohort study design. SETTING: Eleven private day-care centers and preschools in North Carolina participated in the study from January 1, 1995, through December 31, 1999. PARTICIPANTS: All children in the 11 centers were eligible for participation. Some participated more actively, supplying information on a regular basis. Others participated passively. Day-care personnel provided information about all cases of varicella. INTERVENTIONS: None. MAIN OUTCOME VARIABLES: The change in the incidence of varicella disease was documented as the use of varicella vaccine increased. RESULTS: Varicella vaccine coverage increased substantially from 4.4% in 1995 to 63.1% in December 1999. The vaccination rate accelerated dramatically in 1996 and 1997, leveled off in 1998, and rose again in 1999. Cumulative varicella incidence decreased from 16.74 cases per 1000 person-months in July 1996 to 1.53 cases per 1000 person-months in December 1999 in unvaccinated children. CONCLUSIONS: The varicella vaccination rate continued to increase slowly in the day-care population after an initial rapid uptake. The decrease in varicella disease is greater than the increase in varicella vaccination. This herd effect is welcome and even apparent in the unvaccinated children younger than 1 year.

Postlicensure study of varicella vaccine effectiveness in a day-care setting.

BACKGROUND: Varicella vaccine has been licensed for use in the United States since the spring of 1995. The acceptance of the vaccine and its effect on varicella incidence in children is important. AIM: To document the effectiveness of the varicella vaccine in children attending day care in 11 centers in North Carolina. METHODS: A dynamic cohort study design was used in 11 day-care centers in North Carolina. Multiple cross-sectional evaluations were performed and children were noted to be vaccinated or not and diseased or not. Vaccine effectiveness was estimated by comparing the varicella attack rate in the vaccinated with the varicella attack rate in the unvaccinated. Person time was used as the denominator for all calculations. RESULTS: During the study period February 1, 1996, to September 1, 1997, 134 cases of varicella occurred in the unvaccinated and 11 cases occurred in the vaccinated children. The attack rates in the vaccinated and unvaccinated were 2.49 and 14.66, respectively, for an overall vaccine effectiveness of 83% for mild/moderate disease. CONCLUSIONS: In the day-care setting varicella vaccine demonstrated benefit in preventing and modifying wild-type varicella disease.

Concurrent administration of inactivated hepatitis A vaccine with immune globulin in healthy adults.

301 healthy adult volunteers were randomized to one of three treatment groups: inactivated hepatitis A vaccine alone; inactivated hepatitis A vaccine with immune globulin (Ig) concurrently; or Ig alone. The first two treatment groups received a second dose of hepatitis A vaccine at week 24. Anti-HAV was measured 4, 8, 12, 24 and 28 weeks after the primary immunization. When comparing subjects receiving inactivated hepatitis A vaccine alone to those receiving vaccine and Ig, the seropositivity rates were not significantly different at 4, 8, 12 and 28 weeks, but at week 24 the seropositivity rate was lower in the group receiving both vaccine and Ig compared to the group receiving vaccine alone (92.0% compared to 97.0%). At weeks 8, 12 and 24 the geometric mean titers (GMTs) were significantly lower for subjects receiving both vaccine and Ig. The GMTs were not significantly different after the second dose of vaccine. At all time points, the lower serum antibody concentrations observed in subjects receiving both inactivated hepatitis A vaccine and Ig were nevertheless substantially higher than the cutoff for assay seropositivity and much higher than after Ig alone; these differences are therefore clinically insignificant.