SUMMARYSera from an age-stratified sample of 1810 people from the Caribbean island of St Lucia were tested for antibodies against varicella-zoster virus. The results indicate that very few infections occur in childhood, which agrees with clinical survey data from other tropical countries, but contrasts with the observed high case rate in children in temperate countries. The alternative hypotheses which may explain these results are discussed, and it is suggested that high ambient temperatures interfere with the transmission of the virus. Irrespective of the cause, the pattern of varicella incidence observed has important implications for any vaccination policy adopted in tropical countries.
INTROD)UCTIONVaricella (chickenpox), primary infection with varicella zoster virus (VZV), is a very common childhood infection in temperate countries, although the mean age of infection is significantly higher in developing countries [1][2][3][4][5][6][7][8]. This is the reverse of the age pattern observed with many other directly transmitted infections, such as measles, where the mean age of infection is typically low in developing or tropical countries because of a mixture of high population densities, which provide more opportunities for disease transmission, and high birth rates, which provide a large pool of young susceptibles [9]. The reversed age pattern of varicella infection raises questions about the nature of varicella transmission.In order to address these questions this paper discusses the evidence that the force of infection (the per capita rate at which susceptibles acquire infection) of VZV is less in tropical than in temperate countries. The paper examines published reports, describes a serological investigation of the pattern of infection in the population of the Caribbean island of St Lucia and uses the survey data to estimate the age-specific force of infection.The discussion of varicella transmission in this paper centres on differences between tropical and temperate countries. However, tropical countries are usually