Some host populations, particularly in southeast Asia, have been infected at 6 %, and of course such human populations, mostly children under5, deserve vaccine protection. Nonetheless, if 0.006 % of people were infected, 9,994 others would have to be vaccinated to avoid 6/10,000 cases. Then, the urgency of vaccination depends upon the risk of infection. Disease transmission by vector control may reduce the risk so that vaccination is not indicated. Then high-risk areas may indicate the failure of mosquito control. Underreporting cases are common, therefore the risk of infection is routinely underestimated. Misdiagnosis is part of underreporting. Public education is crucial. For instance, the success of a cleanup campaign to reduce mosquito breeding sites depends on public realization of transmission from soft drink containers, old tires and from hiding places in houses.