Academic journal article Journal of Health Population and Nutrition

Seroprevalence of Antibodies to Measles, Mumps, and Rubella among Thai Population: Evaluation of Measles/MMR Immunization Programme

Academic journal article Journal of Health Population and Nutrition

Seroprevalence of Antibodies to Measles, Mumps, and Rubella among Thai Population: Evaluation of Measles/MMR Immunization Programme

Article excerpt

INTRODUCTION

The immunization programme in Thailand, commenced in 1980, currently provides vaccines to protect against 10 childhood diseases, such as tuberculosis, hepatitis B, diphtheria, pertussis, tetanus, poliomyelitis, measles, mumps, rubella, and Japanese encephalitis, through scheduled EPI sessions in hospitals and health centres around the country. The first dose of measles vaccination was incorporated into the national immunization programme for children aged nine months in 1984. The second dose of measles vaccine was added in 1996 for 1st grade students aged seven years. In 1997, the second dose of measles vaccine was replaced by measles-mumps-rubella (MMR) vaccine. Rubella immunization was first provided to 6th grade female students aged 12 years during 1986-1998 and, later, to 1st grade students of both the sexes during 1993-1996 before being replaced by MMR vaccine in 1997 as mentioned above (1). Ages in 2004 of the population under the measles and MMR immunization programme are provided in Table 1. Surveys indicated that the coverage of 1st dose of measles vaccine was 48% in 1987, 82% in 1991, and above 90% since 1996. From the last survey, in 2003, the coverage of 1st dose of measles vaccine was 96% (2). The coverage of MMR vaccine among 1st grade students was 94% surveyed in 2004 (3).

As in other countries, the incidence of measles in Thailand has reduced dramatically since the introduction of live measles vaccine into the routine immunization programme (4-6). The number of reported measles cases reported in the National Disease Surveillance System has declined since 1984 with an outbreak peak every 3-4 years, and mortality due to measles has become extremely rare (Fig. 1). The last peak years were 2001 and 2002 (11.8-16.5 per 100,000 people) (6). The highest incidence was observed in children who were too young for vaccination (7). Outbreaks of measles in children aged less than five years occurred exclusively in hard-to-reach area where the coverage of vaccine was low. Nevertheless, outbreaks among urban and rural children aged 7-15 years still occur occasionally.

In the case of rubella, MMR vaccine is administered to school-age children aiming at preventing congenital rubella syndrome (CRS) and reducing morbidity. The incidence of rubella in Thailand is declining (Fig. 1), the reported rubella morbidity rate in 2003-2006 being only 0.61-0.78 per 100,000 people (6). No outbreak of CRS has been noted in the last 10 years but the significance of this may be questionable as Thailand does not list CRS as a notifiable disease.

The purpose of mumps vaccination in Thailand is to reduce its associated complications and morbidi-ty. The disease-surveillance data show high out- break peaks in 1995-1996 and, after that, the incidence declined. During 2003-2006, the incidence of mumps was 12.2-17.6 per 100,000 people (6).

Although the epidemiological changes seen in the incidence of MMR in Thailand correspond well with immunization history and levels of coverage, the national immunization programme still needs to verify actual levels of immunity. Such information would guide vaccination strategies in both preventing future outbreaks and pursuing the more ambitious targets of elimination or eradication. Accordingly, the main objective of this study was to review the seroprevalence of IgG antibodies to MMR among the Thai population after many years of vaccination against these diseases.

MATERIALS AND METHODS

The Ethical Committee for Research in Human Subjects, Department of Disease Control, Nonthaburi, approved the study. There was no field serum specimen and evidence of data collection specifically for this study. The serum specimens were those remaining from the 2004 hepatitis immunity study (described below). Vaccination history was available only in relation to measles vaccination of children, aged less than five years, who had vaccination cards.

Serum specimens

The sera used in the study were taken from 6,213 existing specimens remaining from a cross-sectional descriptive study of hepatitis immunity in the Thai population in 2004 (8,9). …

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