Measles transmission following the tsunami in a population with a high one-dose vaccination coverage, Tamil Nadu, India 2004-2005

Background: On 26 December 2004, a tsunami struck the coast of the state of Tamil Nadu, India, where one-dose measles coverage exceeded 95%. On 29 December, supplemental measles immunization activities targeted children 6 to 60 months of age in affected villages. On 30 December, Cuddalore, a tsunami-affected district in Tamil Nadu reported a cluster of measles cases. We investigated this cluster to estimate the magnitude of the problem and to propose recommendations for control. Methods: We received notification of WHO-defined measles cases through stimulated passive surveillance. We collected information regarding date of onset, age, sex, vaccination status and residence. We collected samples for IgM antibodies and genotype studies. We modeled the accumulation of susceptible individuals over the time on the basis of vaccination coverage, vaccine efficacy and birth rate. Results: We identified 101 measles cases and detected IgM antibodies against measles virus in eight of 11 sera. Cases were reported from tsunami-affected (n = 71) and unaffected villages ( n = 30) with attack rates of 1.3 and 1.7 per 1000, respectively. 42% of cases in tsunami- affected villages had an onset date within 14 days of the tsunami. The median ages of case-patients in tsunami- affected and un-affected areas were 54 months and 60 months respectively ( p = 0.471). 36% of cases from tsunami- affected areas were above 60 months of age. Phylogenetic analyses indicated that the sequences of virus belonged to genotype D8 that circulated in Tamil Nadu. Conclusion: Measles virus circulated in Cuddalore district following the tsunami, although there was no association between the two events. Transmission despite high one-dose vaccination coverage pointed to the limitations of this vaccination strategy. A second opportunity for measles immunization may help reducing measles mortality and morbidity in such areas. Children from 6 month to 14 years of age must be targeted for supplemental immunization during complex emergencies.