Streptococcus pneumoniae Serotypes Causing Invasive Disease in Children Under 5 Years of Age After the Introduction of the Pneumococcal 13-Valent Conjugate Vaccine in El Salvador.
To the Editors: The incidence of invasive pneumococcal disease (IPD) described by Makwana et al1 from 2010 to 2016 in England, after the introduction of the pneumococcal 13-valent conjugate vaccine (PCV13), was similar to that found in El Salvador, Central America, from 2011 to 2019. PCV13 was introduced to El Salvador in 2011. Between 2011 and 2019, 72 IPD cases in children <5 years of age were reported in El Salvador. A 38.7% decrease in IPD incidence was observed from 2.4 cases/100,000 inhabitants in 2011 to 1.5 cases/100,000 inhabitants in 2019 (P < 0.001), with an average annual decrease of 0.77 cases/100,000 inhabitants. The greatest decrease (52.5%) was observed in the 1–4 years’ age group, where the IPD incidence diminished from 1.9 to 0.9 cases/100,000 inhabitants (P < 0.001). The rates were calculated for each age group under study (<1 year, 1–4 years, >4 to <5 years) using SPSS 26 (IBM, Armonk, NY). As previously stated, PCV13 was introduced in El Salvador in 2011. Two years later, a substantial decrease in vaccine serotypes (VSs) 1, 6 B, 7F, 14, 18C, 19A and 23F was detected. However, from 2011 to 2013, VS 9V continued to be registered, and from 2013 to 2015, new VSs 4, 6A and 19F were reported. In 2014 and 2015, VS 4 was reported once a year. From 2016 to 2018, no VSs were isolated from patients <5 years of age who were diagnosed with IPD. In 2018, PCV13 was replaced with a pneumococcal 10-valent conjugate vaccine (PCV10) for systematic vaccination in children <2 years of age. In 2019, VS 19 F was isolated from pleural fluid clinical samples obtained from two patients diagnosed with pneumonia plus empyema, 1 and 3 years of age, respectively. S. pneumoniae serotyping was interrupted in El Salvador in 2020 owing to the lack of reagents. PCV10 was replaced with PCV13 in 2020. A reduction and even elimination of PCV13 serotypes were registered during the study period, as well as serotype replacement in children <5 years of age diagnosed with IPD, as reported in other countries where PCV13 has been introduced.2,3 Serotype replacement increased from 2011 to 2016 (Fig. 1), rising from one case in 2011 to seven and nine cases in 2015 and 2016, respectively. It decreased again in 2017 (two cases) and 2018 (one case); in 2019, nonvaccine serotypes (NVS) increased again to five cases. From 2011 to 2019, 37 NVS isolates were reported; none are included in the pneumococcal 15-valent conjugate vaccine (PCV15), and 12 (32.4%) are included in the pneumococcal 20-valent conjugate vaccine (PCV20). The distribution of the 12 serotypes was as follows: 8 (four cases), 10A (five cases), 11A (one case), 12F (one case) and 15B (one case). The incidence of PCV13-VS IPD decreased throughout the study period. Nevertheless, as reported by other authors,4,5 the gradual increase in the incidence of PCV13-NVS IPD counteracted the overall effect of PCV13 on the disease burden. The upcoming use of new pneumococcal-conjugated vaccines with a greater spectrum may diminish this phenomenon.FIGURE 1.: Vaccine and nonvaccine serotype replacement in children under 5 years of age diagnosed with invasive pneumococcal disease in El Salvador/2011–2019.ACKNOWLEDGMENTS We thank Mario Sanchez (statistician) and Maria José Luna Boza (Lab technician) for their statistical and laboratory technical advice, respectively.
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