Effect of pneumococcal conjugate vaccination in Uruguay, a middle-income country

Abstract

Background: In 2008, a 7-valent pneumococcal conjugate vaccine (PCV7) was introduced into the routine childhood immunization program in Uruguay, with a 2+1 schedule. In 2010, PCV13 replaced PCV7, and the same 2+1 schedule was used. The effect of these pneumococcal vaccines on the incidence of invasive pneumococcal infections (IPD) and on serotype distribution was analyzed retrospectively, based on passive national laboratory surveillance.

Methods: Data from 1,887 IPD isolates from 5 years before and 5 years after PCV7 introduction (7 before and 3 after PCV13 introduction) was examined to assess the incidence rate per 100,000 age-specific population of all IPD, PCV7-serotypes, and PCV13-serotypes associated IPD among children < 2 years and 2 to 4 years old, and patients ≥ 5 years old. Trends of frequency for each serotype were also analyzed.

Results: Comparison of pre-vaccination (2003-2007) and post-vaccination (2008-2012) periods showed a significant decrease in IPD incidence among children < 2 years old (IR 68.7 to IR 29.6, p<0.001) and children 2 to 4 years (p < 0.04). IPD caused by serotypes in PCV7 was reduced by 95.6% and IPD caused by 6 serotypes added in PCV13 was reduced by 83.9% in children <5 years old. Indirect effects of both conjugate vaccines were observed among patients ≥ 5 years old one year after the introduction of each vaccine, in 2010 for PCV7 and in 2012 for PCV13. Nevertheless, for reasons that still need to be explained, perhaps due to ascertainment bias, total IPD in this group increased after 2007. In 2012, the relative frequency of vaccine serotypes among vaccinated and unvaccinated population declined, except for serotype 3. Non vaccine serotypes with increasing frequency were identified, in rank order: 12F, 8, 24F, 22F, 24A, 15C, 9N, 10A and 33.

Conclusion: Consecutive immunization with PCV7 and PCV13 has significantly reduced IPD in children < 5 years of age in Uruguay.

Figure 1. Incidence of invasive pneumococcal disease (IPD) per 100,000 population: A) patients 0–2 years old; B) patients 2–4 years old; C) patients 5–14 years old; D) patients 15–59 years old; E) patients ≥60 years old.

VT-PCV7: IPD caused by PCV7 serotypes; VT-PCV13: IPD caused by 6 additional serotypes in PCV13; NVT: non vaccine serotypes.

Figure 2. Relative frequency of 13 conjugate vaccine serotypes before and after PCV7 and PCV13 introduction: A) patients <5 years old; B) patients ≥5 years old.

PCV7 and PCV13 were introduced into national immunization program in 2008 and 2010, respectively.