International Journal of Epidemiology, Vol 28, 147-151, Copyright © 1999 by International Epidemiological Association
J Bennett, H Whittle, B Samb, B Cisse, F Simondon and P Aaby
BACKGROUND: Increases in measles antibodies without rash-illnesses have
been documented in previously vaccinated children exposed to measles cases.
The phenomenon has been incompletely evaluated in young unvaccinated
infants with immunity of maternal origin. METHODS: Monthly cohorts of
newborns were prospectively randomized to vaccine and placebo control
groups during a trial of high-titre vaccines in Niakhar, Senegal. Measles
antibodies were assayed in blood samples of enrolled children collected at
5 months old, when controls received a placebo injection, and at 10 months,
when the placebo group was given measles vaccine. Intensive prospective
surveillance for measles was conducted throughout the trial. RESULTS:
One-fifth (n = 53) of the placebo controls seroconverted, with known
exposure to a measles case in only three of them. None of the
seroconverters developed a measles- like rash. Sixteen-fold or greater
increases in titres were noted in about one-quarter of them. Compared with
placebo controls who did not seroconvert, seroconverters were more likely
to have had exposure to a measles case and to travel, more likely to be
boys than girls, and had significantly lower baseline antibody titres.
Measles was endemic in the study area throughout the trial. Seroconversions
did not adversely effect subsequent nutritional indices or mortality.
CONCLUSIONS: Although laboratory errors and inadvertent injection of
vaccine rather than placebo may have played some role, they do not fully
explain the above observations, which are consistent with subclinical
measles in the seroconverters. The possible role of subclinical measles in
occult transmission, its potential effect on the type and duration of
subsequent immunity, and its impact on response to primary vaccination need
to be determined.
ARTICLES
Seroconversions in unvaccinated infants: further evidence for subclinical measles from vaccine trials in Niakhar, Senegal
The Task Force for Child Survival and Development, The Carter Center, Atlanta, GA 30307, USA.
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