Field trial of a heat-stable measles vaccine in Papua New Guinea.

In Papua New Guinea, consideration has been given to the introduction of measles vaccination, and a trial was conducted to determine the optimum age for vaccination and the suitability of a heat-stable measles vaccine (Rimevax) for countrywide use. As much of the vaccination programme is carried out by MCH teams on foot patrols, the trial was designed to determine immunogenicity of the vaccine after being transported and used for a week in a standard issue vaccine Esky by MCH staff. A study of the relevant literature having indicated 9 months as the probable best minimum age for measles vaccination, younger children were not included. The study was carried out on 313 infants and children aged nine to 24 months. An overall seroconversion rate of 96.6% was achieved using initially potent vaccine kept under field conditions for up to 102h. Ninety-seven percent of the vaccinees less than 11 months and 15 days of age seroconverted, as did all 15 children who were less than 70% of the Harvard standard weight for age. All 35 children who had seroconverted and who were retested six months after vaccination had detectable measles antibodies in their serum. Parental recollection of past measles infection was found unreliable as was reporting of post-vaccination reactions by parental recall since the incidence of reported 'reactions' in initially seronegative and seropositive vaccinees were similar. It is concluded that use of this heat-stable vaccine is possible with existing cold chain facilities in PNG and that infants can be vaccinated from the age of 9 months.