Advantage of a two-dose versus one-dose varicella vaccine in healthy non-immune teenagers and young adults.

This study was undertaken to compare the immunogenicity and reactogenicity of two vaccines based on the attenuated Oka-strain of Varicella zoster virus (VZV), in adolescents and young adults. One hundred and eighty-six subjects, aged 13 to 29 years, were randomized to one of two groups to receive a one- or a two-dose VZV vaccine. Pre- and post-vaccination blood samples were assayed for VZV-specific IgG. Solicited local and general symptoms, as well as unsolicited symptoms, were recorded post-vaccination. Seroconversion rates were 94.9% in the one-dose, and 100% in the two-dose, regimen. The two-dose vaccine elicited significantly higher geometric mean antibody titer, 392.5 vs 86.8 pfu. Transient local injection site pain was the most frequently-reported symptom per dose in both groups (one dose: 48.9%; two-dose: 32.8%). The two-dose vaccine regimen afforded the advantage of higher antibody titers and potential increased protection from disease, without significantly increased reactogenicity.

Effect of climatic factors and population density on varicella zoster virus epidemiology within a tropical country.

Blood samples were collected from healthy subjects, aged 9 months-29 years in urban and rural communities from 4 distinct regions in Thailand, to determine the seroprevalence rate of varicella-zoster virus (VZV) antibody and its relationship with demographic, climatic, and socioeconomic factors. The overall seroprevalence rate was 52.8% and increased from 15.5% in the 9-month to 4-year-old group to 75.9% in the 20-29 year-olds. The age-adjusted seroprevalence was significantly higher in the cooler than in the warmer regions. In the warmer regions only, the age-specific seroprevalence was significantly higher in the urban population than in the rural population. In Thailand, climate is the main determinant of VZV seroprevalence. The delayed onset of natural immunity is more marked in warmer climate areas. Population density is a secondary determinant; in the warmer areas, the pattern of adolescent and adult susceptibility was greater in rural than in urban areas.

Comparison of the reactogenicity and immunogenicity of two different dose levels of hepatitis A vaccine in healthy children and adolescents.

An open study was performed to compare the reactogenicity and immunogenicity of an inactivated hepatitis A vaccine administered in two different doses and schedules to 460 healthy volunteers aged 3-18 years. Participants were randomized to two groups to receive either two doses of 720 ELISA Units (EL.U) inactivated hepatitis A per 0.5 ml dose according to a 0, 6-month schedule, or three doses of 360 EL.U according to a 0, 1, 6-month schedule. Transient local injection soreness was the most commonly reported symptom in almost half of both groups with no serious adverse events. One month after the primary course (one dose of 720 EL.U and two doses of 360 EL.U), 99% of 720 EL.U vaccinees had seroconverted, compared with 100% seroconversion in the 360 EL.U group. All vaccinees were seropositive after the booster dose of both vaccines with geometric mean anti-HAV titers of 2,359 and 2,967 mIU/ml in the 720 EL.U and 360 EL.U groups, respectively. The vaccine containing 720 EL.U of antigen per dose offers the advantage of convenience and acceptance of immunization afforded by a two-dose course of vaccination accompanied by a comparable antibody response with that achieved after three doses of vaccine containing 360 EL.U of antigen per dose.

Seroepidemiology of hepatitis A virus antibody in primary school children in Khon Kaen Province, northeastern Thailand.

Hepatitis A is a disease commonly found in Thai children. Since 1984, there have been very few reports on the age specific prevalence of hepatitis A virus infection in the northeastern part of Thailand, which has the largest population and is the poorest area of the country. We studied the seroprevalence of hepatitis A virus (HAV) antibody in 3 primary school children in different areas of Khon Kaen Province, northeastern Thailand. Anti-HAV level was assayed by ELISA. Four hundred and forty-one children age 6-12 years were selected from one primary school in the urban area and two from rural areas. The highest prevalence was 22.6% at age 12 years and 0 at age 6 years. The seroprevalence was highest, 45%, in rural school children of the lowest socioeconomic status as compared to 10.8% and 2.6% in other urban school children. The overall prevalence was 12.7% and the age specific prevalence with 95% CI are presented. These data indicated a much lower seroepidemiological prevalence than previously reported and might be related to the level of socioeconomic and standard of public sanitation and living conditions.

The pattern of diarrhea in children in Khon Kaen, northeastern Thailand: I. The incidence and seasonal variation of diarrhea.

The incidence, seasonal variation and risk factors of diarrhea in children in Thailand are not well defined. The objective of this study is to identify the incidence and seasonal variation of diarrhea in a rural community. A cohort of 481 children under five years of age from 14 villages in rural northeastern Thailand was followed for 1 year, from May 1988 to April 1989. The data were collected daily by 5 participant observers who resided in the villages during the study period. During the 25,012 person weeks of surveillance, 384 episodes of diarrhea occurred; 279 episodes (72.7%) were watery diarrhea and 105 episodes (27.3%) were dysentery-like diarrhea. The incidence of diarrhea was 2.1, 1.76, 0.96 and 0.45 episodes per child per year for children aged 0-6 months, 7-12 months, 1 year and above 2 years, respectively. Males were affected as frequently as females. The average duration of illness was 4.9, 2.1, 1.5 and 0.5 days per child per year for children aged under 1 year, 1-2 years, 2-3 years and more than 3 years old, respectively. Both dysentery and watery diarrhea rates peaked for children of all ages from May to July, during the early rainy season. A second peak of watery diarrhea in the winter from November to January and was seen primarily in children less than 2 years old. The monthly incidence of diarrhea was associated with rainfall, ambient temperature and occupational behavior of people in each season.