Effectiveness of 13-valent pneumococcal conjugate vaccine against vaccine-serotype community acquired pneumococcal diseases among children in China: A test-negative case-control study

Background: In 2016, China licensed 13-valent pneumococcal conjugate vaccine (PCV13) based on a study that demonstrated its immunogenicity is non-inferior to PCV7. However, the real-world effectiveness of PCV13 against vaccine-serotype pneumococcal diseases in China has limited evidence. Methods: A test-negative case-control study was conducted among children under 5 years old admitted to the Children's Hospital of Soochow University (SCH) with respiratory tract infections from January 2018 to December 2020. Cases were defined as children from whom the isolates were tested positive for Streptococcus pneumoniae (S. pneumoniae) with serotypes included in PCV13. Two control groups were included, one represented children with isolates positive for S. pneumoniae of non-PCV13 serotypes and the other comprised children who tested negative for S. pneumoniae. The S. pneumoniae-negative controls were selected by matching them to the cases based on gender, age and admission date in a 1:1 ratio. Vaccine effectiveness (VE) was calculated using a logistic regression model as (1- adjusted odds ratio) * 100 %. Results: A total of 2371 pneumococcal isolates were included in the analysis, of which 75.0 % (1779/2371) were covered by PCV13 serotypes. Consequently, these 1779 children were classified as cases, and 592 children were designated as non-PCV13 serotype controls. Another 1779 children were correspondingly recruited as S. pneumoniae-negative controls. Overall, 40 cases (2.3 %) and 148 controls (6.2 %) had received vaccination. The overall VE in the PCV13/non-PCV13 serotypes case-control study was 50.0 % (95 % CI: 15.0, 70.7), which was lower than the VE of 74.4 % (95 % CI: 60.7, 83.3) in the matched PCV13/S. pneumoniae-negative casecontrol study. VE was higher for >= 2 or >= 3 doses of vaccination compared to >= 1 dose. VE against specific PCV13 serotypes (6B, 6A and 19F) was higher than for other serotypes. Conclusions: PCV13 vaccination demonstrates effectiveness against vaccine-serotype pneumococcal diseases in children, particularly for serotypes 6B, 6A and 19F.