370Measuring pneumococcal conjugate vaccine impact in a low-resource setting with minimal baseline data

Abstract Background We aimed to measure 13-valent pneumococcal conjugate vaccine (PCV13) impact on various pneumococcal endpoints with minimal baseline data. Methods PCV13 was introduced in October 2013 in Lao People’s Democratic Republic. We implemented studies to evaluate PCV13 impact: retrospective record review of pneumonia cases for three years pre-PCV13; prospective study of acute respiratory infection (ARI) for 4.5 years post-PCV to demonstrate effectiveness against hypoxic pneumonia; invasive pneumococcal disease (IPD) surveillance (2004-2019); carriage in children hospitalised with ARI (2013-2019); and community carriage surveys pre- and two years post-PCV13. Results Annual incidence of hospitalized pneumonia pre-PCV13 in children 2-59 months was 1,530 (95% confidence interval [CI] 1,477-1,584) per 100,000. Vaccine effectiveness against hypoxic pneumonia was 37% (95% CI 6-57%). In children <5 years, 85% (11/13) of IPD cases were due to PCV13 serotypes pre-PCV13, and 43% (3/7) post-PCV13; and in individuals ≥5 years, 61% (27/44) and 42% (17/40), respectively. In hospitalised children, vaccine type carriage prevalence reduced from 20.0% (95% CI 15.2-24.9%) in 2013 to 12.8% (95% CI 8.5-17.1%) in 2019 with increasing vaccine coverage. Results were consistent with community carriage studies. Conclusions Despite limited baseline data in Laos, we found evidence of PCV13 impact using a variety of methods. Our approach could be used in similar settings to augment existing WHO guidelines. Key messages A combination of methods may be useful to determine the impact of vaccine introduction in countries with limited surveillance.