When the World Health Organization launched a campaign in 2000 to eliminate measles through mass vaccination, measles deaths among young children were slashed by 91 percent in Africa, which comprised 70 percent of the global burden.
To keep the disease from reemerging, the WHO recommends that countries vaccinate at least 90 percent of their children every few years.
But measles started to reappear again in Zambia as the country eased up on vaccination efforts.
In a study published this week in the journal The Lancet, researchers surveying 679 children in three townships in Lusaka found that only 67 percent showed immunity to measles, a sign that fewer than 90 percent or more of young children had been vaccinated against the potentially deadly, highly infectious disease.
Researcher William Moss, of the Bloomberg School of Public Health in Baltimore, Maryland, and colleagues looked at the situation in Zambia three years after a mass vaccination campaign in 2003. Moss says this unvaccinated population poses a serious public health threat.
"What our survey showed is that over time, the number of susceptible children increased, creating the possibility for a larger and more severe measles outbreaks," said Moss. Moss says Zambia also has one of the highest rates of HIV in Africa, but the study found that the presence of HIV-infected children didn't significantly decrease the effectiveness of the measles vaccination campaign. To conduct their study, Moss took cheek swabs from the children and analyzed them for antibodies to the measles virus, a sign that the youngsters had been vaccinated.
Moss believes the survey technique he and his colleagues used could be an important tool in targeting and monitoring the effectiveness of future vaccination campaigns, which are costly burdens on a country's health care system. "So, we believe this that this type of survey might be useful in helping countries determine the timing of campaigns," added Moss. Proper timing would keep enough people with immunity in the population to interrupt measles virus transmission, without spending precious funds on unnecessary vaccinations.
Moss also says Zambia began a vaccination campaign in 2007 to stop outbreaks of the disease, but the study authors conclude that was too late and say that based on the evidence, it would have been better if a countrywide campaign had been started the a year earlier.
By Jessica Berman Washington 10 February 2009
