Using the Indirect Cohort Design to Estimate the Effectiveness of the Seven Valent Pneumococcal Conjugate Vaccine in England and Wales
et al. (2011) Using the Indirect Cohort Design to Estimate the Effectiveness of the Seven Valent
Pneumococcal Conjugate Vaccine in England and Wales. PLoS ONE 6(12): e28435. doi:10.1371/journal.pone.0028435
Using the Indirect Cohort Design to Estimate the Effectiveness of the Seven Valent Pneumococcal Conjugate Vaccine in England and Wales
Nick Andrews 0
Pauline A. Waight 0
Ray Borrow 0
Shamez Ladhani 0
Robert C. George 0
Mary P. E. 0
Slack 0
Elizabeth Miller 0
Lorenzo Aguilar, Universidad Complutense, Spain
0 1 Statistics, Modelling and Economics Department, Health Protection Services, Health Protection Agency , London , United Kingdom , 2 Immunisation , Hepatitis and Blood Safety Department, Health Protection Services, Health Protection Agency , London , United Kingdom , 3 Vaccine Evaluation Unit, Microbiology Services Division, Health Protection Agency , Manchester , United Kingdom , 4 Respiratory and Systemic Infection Laboratory , Microbiology Services Division, Health Protection Agency , London , United Kingdom
Background: The 7-valent pneumococcal conjugate vaccine (PCV-7) was introduced in the United Kingdom in 2006 with a 2,3 and 13month schedule, and has led to large decreases in invasive pneumococcal disease (IPD) caused by the vaccine serotypes in both vaccinated and unvaccinated cohorts. We estimated the effectiveness of PCV-7 against IPD. Methods and Findings: We used enhanced surveillance data, collated at the Health Protection Agency, on vaccine type (n = 153) and non vaccine type (n = 919) IPD cases eligible for PCV-7. The indirect cohort method, a case-control type design which uses non vaccine type cases as controls, was used to estimate effectiveness of various numbers of doses as well as for each vaccine serotype. Possible bias with this design, caused by differential serotype replacement in vaccinated and unvaccinated individuals, was estimated after deriving formulae to quantify the bias. The results showed good effectiveness, increasing from 56% (95% confidence interval (CI): -7-82) for a single dose given under one year of age to 93% (95% CI: 7098) for two doses under one year of age plus a booster dose in the second year of life. Serotype specific estimates indicated higher effectiveness against serotypes 4, 14 and 18C and lower effectiveness against 6B. Under the assumption of complete serotype replacement by non vaccine serotypes in carriage, we estimated that effectiveness estimates may be overestimated by about 2 to 5%. Conclusions: This study shows high effectiveness of PCV-7 under the reduced schedule used in the UK. This finding agrees with the large reductions seen in vaccine type IPD in recent years in England and Wales. The formulae derived to assess the bias of the indirect cohort method for PCV-7 can also be used when using the design for other vaccines that affect carriage such as the recently introduced 13 valent pneumococcal conjugate vaccine.
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Funding: Funding was provided by the Health Protection Agency. The funder had no role in study design, data collection and analysis or preparation of the
manuscript. The funder approved the submission of the manuscript.
Competing Interests: RB has performed contract research on behalf of the Health Protection Agency that was funded by Pfizer, GlaxoSmithKline, Sanofi
Pasteur, and Merck. MS has received assistance to attend scientific meetings from Pfizer and GlaxoSmithKline and research funding from Pfizer and
GlaxoSmithKline. RG has received support for conference attendance from Pfizer and GlaxoSmithKline, and his laboratory has received research funding from
Pfizer and GlaxoSmithKline. SL has received assistance to attend scientific meetings from Pfizer and GlaxoSmithKline. This declaration does not alter the authors
adherence to all the PLoS ONE policies on sharing data and materials. None of the funding from Pfizer, GlaxoSmithKline, Sanofi Pasteur, or Merck was used
specifically for this study.
The 7-valent pneumococcal conjugate vaccine (PCV-7;
Prevenar, Pfizer) was first licensed in the United States in 2000 as a
3+1 dose schedule following evidence of high efficacy in children
from randomized controlled trials [1]. The vaccine has since been
introduced in many countries, including the United Kingdom in
September 2006, where a reduced 2 +1 schedule at 2, 4 and13
months was used together with a single dose catch-up for children
aged between 12 and 24 months. This reduced schedule was based
on immunogenicity rather than efficacy data, and therefore
required post-licensure assessment of effectiveness [2].
Within a few years of introduction there was a considerable
reduction of vaccine-type invasive pneumococcal disease (VT
IPD) in both the vaccine-targeted age groups and older age groups
through herd immunity in England and Wales [3]. Some of these
reductions have, however, been offset by increases in non-vaccine
type IPD (NVT IPD) through replacement as documented in a
recent review [4]. A higher valency pneumoco (...truncated)