The vaccine for whooping cough commonly administered to young children loses its effectiveness after three years, according to the preliminary results of a new US study. The results released on September 19 come from a survey of 15,000 children in Marin County, California, where an outbreak of the bacterial disease killed 11 infants and infected more than 8,000 people in 2010.
"When we first started having a pertussis outbreak, we assumed that this would be primarily in the unvaccinated population," Dr David Witt, of Kaiser Permanente Medical Centre in San Rafael, California told a conference in Chicago, using the scientific name for the once-common childhood disease.
"What we pretty quickly identify is that the bulk of the outbreak was in fully vaccinated children" in the 8-12 age group, he said.
He added that a lot of the children did not seek care because the vaccine mitigated the symptoms.
He cautioned that more research was necessary as he presented the preliminary results at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) organised by the American Society of Microbiology. In the group of 15,000 children surveyed, doctors found 171 confirmed cases of whooping cough across all age groups, including 103 in the group of eight to 12-year-olds.
These children were up to 20 times more likely to become infected than those whose last booster injection was more recent, Witt said.
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