The battle to continue reducing measles deaths and illness in Africa is one that can only be won with high measles vaccination coverage, achieved through repeated mass vaccination campaigns and high routine vaccine coverage. But many countries in Africa face challenges, such as difficulties maintaining high levels of routine measles vaccination coverage, high HIV prevalence, and potential clustering of susceptible people, particularly in densely populated urban areas. The issues are discussed in an Article published Online First and in an upcoming edition of The Lancet, written by Dr William J Moss and Dr Sara A. Lowther, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA, and colleagues.
The authors did a cross-sectional survey in Lusaka, Zambia, to assess population immunity to the measles virus three years after a mass vaccination campaign in a region with high HIV prevalence. Households were randomly selected from a satellite image, and children aged 9 months to 5 years were eligible. The children's caregivers were given questionnaires about measles vaccination and measles history. Oral fluid samples were obtained and tested for antibodies to both HIV and measles.
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. Only 679 children (67%) had antibodies to measles virus, and 64 (6%) children had antibodies to HIV. Children with antibodies to HIV were as likely to have no history of measles vaccination as those without antibodies to HIV. In vaccinated children, 33 (61%) of 54 children with antibodies to HIV also had antibodies to measles virus, compared with 568 (71%) of 796 children without antibodies to HIV.
The authors conclude: "3 years after an SIA, 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 SIAs.
"One of the challenges to continued progress in reducing measles incidence and mortality is the need for repeated mass measles vaccination campaigns. These campaigns require the sustained commitment of resources and personnel, are typically done within 3-4 years of the initial campaign, and target a narrower age-group than initial catch-up campaigns. Cross-sectional surveys such as this, using oral fluid specimens and satellite images for sampling, could be useful to identify the optimum timing of repeat SIA before large outbreaks of measles occur."
In an accompanying Comment, Dr Robin J Biellik, Immunization Solutions, PATH, Ferney-Voltaire, France, and Dr David Brown, Health Protection Agency, London, UK, say: "Lowther's study, together with other recent reports, shows how seroepidemiology with oral fluid can provide important information to support measles work in Africa and elsewhere.
"The wider exploitation of these tools would be facilitated by further studies to define cost-effective population sampling and assay performance, and by greater commercial and funding-agency interest in oral-fluid testing."
Dr William J Moss, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA T) +1 410-502-1165 E) wmoss@jhsph.edu
Dr Robin J Biellik, Immunization Solutions, PATH, Ferney-Voltaire, France (recently retired) contact by e-mail E) rbiellik@gmail.com
For full Article and Comment, please see: http://press.thelancet.com/measlesafricafinal.pdf
Journal
The Lancet