Safia Bibi, Taranum Ruba Siddiqui, Syed Furqan Hasan, Waquaruddin Ahmed.
Colonizing pneumococcal serotypes in Pakistani children (<3 years) before the introduction of pneumococcal conjugate vaccine - implications for vaccine formulation.
Pak J Med Res Jan ;57(4):138-43.

Background: Pneumococcal vaccine prevents pneumococcal infections by inhibiting pneumococcal colonization in the host. As pneumococcal vaccine covers limited pneumococcal serotypes, hence knowledge of prevalent pneumococcal serotypes in a population is critical to estimate the effectiveness of vaccine in that population. This is the first study from Pakistan that reports colonization rates and colonizing pneumococcal serotypes in Pakistani children during pre-vaccination era. Study design, settings and duration: A cross sectional study was conducted at PHRC Research Centre, Jinnah Postgraduate Medical Centre (JPMC), Karachi in collaboration with EPI Centre, National Institute of Child Health (NICH), Karachi during one year. Materials and Methods: The study was conducted in continuation with a previous study in which nasopharyngeal swabs of healthy children coming to NICH for the EPI vaccination were collected and cultured for the presence of S. pneumoniae. Pneumococcal isolates were stored frozen in skimmed milk tryptone glucose glycerol (STGGA) medium. These isolates were then revived and serotyped using multiplex PCR as per the recommendations of Centre for Disease Control (CDC), USA to find out if the serotypes identified are being covered by recently introduced pneumococcal vaccine. Results: Out of total, 61 (31%) pneumococcal isolates that were recovered from nasopharyngeal swabs of 192 healthy children, 58 (95.1%) isolates could be revived and were serotyped. The most prevalent serogroup in was identified to be 6A/6B/6C/6D which was isolated from 9 (15.5%) of children followed by 19F, 4 (6.9%). Both serotypes were covered by 10-valent pneumococcal vaccine. Overall 23(39.7%) isolates were covered by 10-valent vaccine and 26 (44.8%) by 13-valent pneumococcal conjugate vaccine. Predominant serotypes or serogroups in our population that were not being covered by both of these vaccines were 13F, 10F/10C/33C and 38/25F/25A, each was isolated from 4(6.9%) constituting 20.7% non-vaccine serotypes. Conclusion: Serotype coverage of PCV-10 was low in Pakistani children which could be improved by using PCV-13. Policy message: The findings will be be helpful 1) for authorities to identify the appropriate vaccine for our population and 2) for industry to formulate a vaccine with a serotype combination that may give desired results to prevent pneumococcal infections in our population.

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