4. Discussion
4.1. Summary of main findings
We have found that half of UK children acquire chickenpox by age 3 and almost three quarters by age 5 based on maternal reporting. The true prevalence estimates are likely to be even higher due to under-reporting of sub-clinical or mild infections. Our findings support the hypothesis that increased social contact with other children, either in the household or through attendance at day care nursery increases the risk of chickenpox, and that their influence varies by age. Household contact with other children and day care attendance appear to be more important in predicting risk of infection by 3 years than between ages 3 and 5 years. We also found a higher risk of infection by 5 years of age in children whose mothers were White or of higher socio-economic status although the importance of these factors appears to vary with age at acquisition. In addition, children born to professional mothers are more likely to acquire chickenpox by age 3 years than between 3 and 5 years. However, the influence of maternal ethnic status is more important between ages 3 and 5 years particularly for children of Black mothers who are more likely to acquire infection between ages 3 and 5 years than by age 3.