Effectiveness of the conjugate pneumococcal vaccines against clinically suspected invasive pneumococcal disease in New Zealand

Abstract

Introduction Pneumococcal conjugate vaccines (PCVs) have proven successful in reducing global rates of invasive pneumococcal disease (IPD). Most countries have measured PCV effectiveness using laboratory surveillance methods only. Data examining sociodemographic differences in IPD and vaccine effectiveness (VE) are scarce. Recent evidence suggests clinically suspected invasive pneumococcal disease (CSIPD), described by hospitalisation discharge codes and excluding laboratory confirmed disease, captures a larger proportion of clinically significant IPD. We analysed PCVs effectiveness against CSIPD in New Zealand (NZ) children. Methods A retrospective cohort study using NZ national administrative data from 2008-2015 was undertaken. It included all children aged under 6 years who were born in 2008-2015 and were eligible to receive the NZ infant PCV schedule. We defined CSIPD based on ICD-10-AM codes compatible with IPD (A40.3, B95.3, G00.1, and M00.1) and unspecified sepsis and/or infection (A40.9, A41.9, A49.9, G00, G00.9, I30.1, M00, M00.9, and B95.5). Laboratory confirmed cases were removed. Vaccinated was defined as 14 days after receiving two vaccinations at least 3 weeks apart, after 38 days of age. VE was estimated using 1-Odds Ratios (OR). Results The cohort included 466,252 (83.8%) vaccinated, and 90,183 (16.2%) unvaccinated children. There were 1,417 CSIPD events in children aged 6 weeks to 5 years. Of this, there were 461 unvaccinated cases (0.5% of unvaccinated), and 956 vaccinated cases (0.2% of vaccinated). Of the cases, 35.1% identified as Māori, and 18.3% as Pacific peoples. Also, 37.8% of cases were in the highest deprivation quintile. The unadjusted VE was 60% (95% CI; 55, 64). When adjusted for sex, ethnic group, deprivation level, district health board, and year of birth, VE was 64% (95% CI; 60, 68). Māori had an adjusted VE of 84% (95% CI; 0.81, 0.87), Pacific peoples 81% (95% CI; 75, 85), and NZ European, Other, and Asian 54% (95% CI; 0.45, 0.62). The most deprived group had a VE of 82% (95% CI; 79, 85), and the least deprived 46% (95% CI; 21, 63). Conclusions PCVs have been effective against CSIPD in NZ children between 2008 and 2015, especially among Māori, Pacific peoples, and high deprivation groups.