CASE PRESENTATION: A previously healthy 7-month old infant presented initially with fever, cough and coryza, and subsequently developed Koplik's spots followed by a typical morbilliform skin rash. There was significant contact history with a household relative who had recently been diagnosed with measles. On examination, a 2.5 cm area of erythema and induration was seen at the previous BCG inoculation site, in addition to the widespread maculopapular rash. No other clinical features of KD were present. Measles virus was isolated from the throat swab and measles antibodies (IgM) were present in the serum. The patient recovered completely with oral vitamin A and supportive therapy, and had normal echocardiography examination on follow up.
CONCLUSIONS: This case report highlights the rare finding of BCG reactivation in a child with confirmed measles infection, and suggests that this clinical manifestation may occasionally occur in children with infections or conditions other than KD.
METHODS: We define effective vaccine coverage (EVC) of measles as the proportion of a population vaccinated with measles-containing vaccine (MCV) and effectively protected against measles infection. A quantitative evaluation of EVC throughout the life course of Malaysian birth cohorts was conducted accounting for both vaccine efficacy (VE) and between-dose correlation (BdC). Measles vaccination coverage was sourced from WHO-UNICEF estimates of Malaysia's routine immunisation coverage and supplementary immunisation activities (SIAs). United Nations World population estimates and projections (UNWPP) provided birth cohort sizes stratified by age and year. A step wise joint Bernoulli distribution was used to proportionate the Malaysian population born between 1982, the first year of Malaysia's measles vaccination programme, and 2021, into individuals who received zero dose, one dose and multiple doses of MCV. VE estimates by age and doses received are then adopted to derive EVC. A sensitivity analysis was conducted using 1000 random combinations of BdC and VE parameters.
RESULTS: This study suggests that no birth cohort in the Malaysian population has achieved > 95% population immunity (EVC) conferred through measles vaccination since the measles immunisation programme began in Malaysia.
CONCLUSION: The persistence of measles in Malaysia is due to pockets of insufficient vaccination coverage against measles in the population. Monitoring BdC through immunisation surveillance systems may allow for the identification of susceptible subpopulations (primarily zero-dose MCV individuals) and increase the coverage of individuals who are vaccinated with multiple doses of MCV. This study provides a tool for assessment of national-level population immunity of measles conferred through vaccination and does not consider subnational heterogeneity or vaccine waning. This tool can be readily applied to other regions and vaccine-preventable diseases.