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Seven-valent pneumococcal conjugate vaccine (PCV7) was included in the UK national immunisation program in 2006, and this was replaced by thirteen-valent PCV in 2010. During this time, the carriage of vaccine-type Streptococcus pneumoniae decreased but pneumococcal carriage remained stable due to increases in non-vaccine-type S. pneumoniae. Carriage studies have been undertaken in various countries to monitor vaccine-type replacement and to help predict the serotypes, which may cause invasive disease. There has been less focus on how conjugate vaccines indirectly affect colonization of other nasopharyngeal bacteria. If the nasopharynx is treated as a niche, then bacterial dynamics are accepted to occur. Alterations in these dynamics have been shown due to seasonal changes, antibiotic use, and sibling/day care interaction. It has been shown that, following PCV7 introduction, an eradication of pneumococcal vaccine types has resulted in increases in the abundance of other respiratory pathogens including Haemophilus influenzae and Staphylococcus aureus. These changes are difficult to attribute to PCV7 introduction alone and these studies do not account for further changes due to PCV13 implementation. This review aims to describe nasopharyngeal cocarriage of respiratory pathogens in the PCV era.

Background: Asymptomatic carriage of the opportunistic pathogen Streptococcus pneumoniae is known to precede the development of invasive disease. Young children are one of the major reservoirs for pneumococci and worldwide over 700,000 children under two years old die due to invasive pneumococcal disease each year. Heptavalent conjugate vaccine (PCV-7) was introduced into the UK childhood immunisation schedule in September 2006. Our objective was to assess the emergence of colonising serotypes in young children in the three years following PCV-7 implementation., Methods: Time-series prevalence survey set in the paediatric outpatients department of a large UK teaching hospital. Participants were children aged four years and under attending the outpatients department during PCV-7 introduction (October 2006-February 2007) and in the same months of the two subsequent years. The main outcome measure was prevalence of pneumococcal carriage by serotype., Results: The rate of pneumococcal nasopharyngeal carriage remained stable during the three year period. We observed a significant 69% (95% CI, -40% to -118%, p<0.0001) decrease in carriage of PCV-7 serotypes during PCV-7 implementation and a concomitant increase in the proportion of non PCV-7 serotypes. The most prevalent emerging non-vaccine serotypes were 6C, 11A, 19A and 22F. By March 2009, PCV-13 was predicted to cover only 33.3% (95% CI, 24.2-42.5%) of strains carried in the study population., Conclusions: Although the overall pneumococcal carriage rate remained stable between 2006 and 2009, we observed a significant decrease in the serotype coverage of PCV-7 and PCV-13. PCV-7 was highly successful in reducing carriage of vaccine serotypes. However, the increase in the proportion of non-vaccine serotypes found both in our study and causing invasive disease currently in the UK, underlines the importance of continued surveillance of carriage and disease., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

We sought to determine the potential impact of seven-valent pneumococcal conjugate vaccine on the incidence of invasive pneumococcal disease (IPD) among children in Scotland. Invasive pneumococci from blood and cerebrospinal fluid, isolated between 2000 and 2004 from all children aged less than 5 years in Scotland, were characterized by serotyping. Using reported efficacy data of the seven-valent pneumococcal conjugate vaccine (PCV7) along with likely coverage rates, we made an estimation of the potential impact on the incidence of IPD among children in Scotland. A total of 217 pneumococci were characterized into 22 different serogroups/types, the most common, in rank order, being 14, 19F, 6B, 18C, 23F, 9V, 4, 1, 19A, and 6A. Estimated serotype coverage for PCV7 was 76.5% in those aged less than 5 years of age but increased to 88.9% for those aged 1 year. By using serotype coverage and estimates of vaccine efficacy and uptake, the potential impact of the vaccine for those greater than 2 months of age, but less than 5 years, was estimated as 67.3%, leading to an average of 29 preventable cases per year. The introduction of PCV7 into the childhood immunization schedule would reduce the burden of pneumococcal disease in children, and the incidence would be particularly reduced in those children aged 1 year. Additional benefits may be gained in adults through herd protection. Continued surveillance of IPD is required before, during, and after the introduction of PCV7.