Population immunity to measles virus and the effect of HIV

Population immunity to measles virus and the effect of HIV-1 infection after a mass measles vaccination campaign in Lusaka, Zambia: a cross-sectional survey.

Measles control efforts are hindered by challenges in sustaining high vaccination coverage, waning immunity in HIV-1-infected children, and clustering of susceptible individuals. The authors’ aim was to assess population immunity to measles virus after a mass vaccination campaign in a region with high HIV prevalence. 3 years after a measles supplemental immunisation activity (SIA), they undertook a cross-sectional survey in Lusaka, Zambia. Households were randomly selected from a satellite image. Children aged 9 months to 5 years from selected households were eligible for enrolment. A questionnaire was administered to the children’s caregivers to obtain information about measles vaccination history and history of measles. Oral fluid samples were obtained from children and tested for antibodies to measles virus and HIV-1 by EIA. 1015 children from 668 residences provided adequate specimens. 853 (84%) children had a history of measles vaccination according to either caregiver report or immunisation card. 679 children (67%) had antibodies to measles virus, and 64 (6%) children had antibodies to HIV-1. Children with antibodies to HIV-1 were as likely to have no history of measles vaccination as those without antibodies to HIV-1 (odds ratio [OR] 1.17, 95% CI 0.57-2.41). Children without measles antibodies were more likely to have never received measles vaccine than those with antibodies (adjusted OR 2.50, 1.69-3.71). In vaccinated children, 33 (61%) of 54 children with antibodies to HIV-1 also had antibodies to measles virus, compared with 568 (71%) of 796 children without antibodies to HIV-1 (p=0.1). 3 years after a supplemental immunisation activity, population immunity to measles was insufficient to interrupt measles virus transmission. The use of oral fluid and satellite images for sampling are potential methods to assess population immunity and the timing of supplemental immunisation activities.

The WHO/UNICEF strategy for measles mortality reduction requires more than 90% routine measles vaccine coverage, a second opportunity for measles vaccination, effective case-based surveillance, and appropriate clinical management for children with measles. This Lusaka household survey did not find that HIV-infected children contributed disproportionately to the pool of susceptible children however, this may have been due to the high mortality already experienced by HIV-infected children who had encountered measles. There was a non-statistically significant but nonetheless concerning difference in measles antibody detection between HIV-infected children and other children. This, in addition to the low levels in the general paediatric population of both a history of measles vaccine and detectable antibody, suggests that there is a high risk of measles outbreaks in Lusaka and that will translate into disproportionate morbidity and mortality for children with HIV infection.