21 October 2011
A study led by the Medical Research Council in The Gambia in collaboration with the London School of Hygiene & Tropical Medicine and published in this week’s PLoS Medicine shows for the first time in Africa, that vaccinating young children against the pneumococcus (a bacterium that can cause fatal infections) causes a herd effect in which the entire community is protected against this infection..
As an alternative method to long-term observational studies and to anticipate the potential long term effects of the introduction of pneumococcal conjugate vaccination in sub-Saharan Africa, the authors conducted a village-randomized trial in The Gambia in which the whole population of some villages were immunized with pneumococcal conjugate vaccine (PCV-7) (vaccinated villages) and in other villages only children <30 months of age at vaccination or other children born during the trial received PCV-7 while older residents received a control vaccine (control villages).
Before immunization, the overall prevalence of pneumococcal carriage in both groups was high at 71.1% and decreased with age. The overall prevalence of pneumococcal carriage at 6, 12, and 22 months after vaccination was similar between vaccinated and control villages, showing a marked fall. However, the prevalence of carriage of vaccine serotype pneumococci was significantly lower in vaccinated than in control villages in all surveys for all age groups. The authors also found that the overall prevalence of pneumococcal carriage fell markedly after vaccination and reached minimum levels at 12 months after vaccination in both study arms and in all age groups.
The authors, led by Anna Roca from the MRC in The Gambia say: “We have shown here, to our knowledge for the first time in Africa, a herd effect on carriage of [vaccine serotype] pneumococci, which might be translated into herd protection against [invasive pneumococcal disease] in adults, following routine immunization of infants and young children.”
They conclude: “Our findings are relevant for other countries in Africa contemplating the introduction of [pneumococcal conjugated vaccines] where the pattern of pneumococcal infection is similar to that in The Gambia.”
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