Investigating the pertussis resurgence in England and Wales, and options for future control.

Yoon Hong Choi,Albert Jan Van Hoek,Gayatri Amirthalingam,Helen Campbell,Elizabeth Miller

doi:10.1186/s12916-016-0665-8

Yoon Hong Choi, Albert Jan Van Hoek + Show 3 more

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https://doi.org/10.1186/s12916-016-0665-8

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Abstract

BackgroundIn 2012 England and Wales experienced a resurgence of pertussis and an increase in infant deaths. This occurred 8 years after acellular pertussis (aP) vaccine replaced whole cell (wP) primary vaccine despite continued high coverage for the primary series and pre-school aP booster. We developed a mathematical model to describe pertussis transmission dynamics in England and Wales since the 1950s and used it to investigate the cause of the resurgence and the potential impact of additional vaccination strategies.MethodsAn age-structured, compartmental, deterministic model of the pertussis transmission dynamics was fitted to 60 continuous years of age-stratified pertussis notification data in England and Wales. The model incorporated vaccine-induced and natural immunity and differentiated between vaccine-induced protection against clinical disease and infection.ResultsThe degree of protection of wP vaccine against infection was estimated to be higher than that of aP vaccine. Furthermore, the duration of protection for natural and wP-induced immunity was likely to be at least 15 years, but for aP vaccine it could be as low as 5 years. Model results indicated that the likely cause of the resurgence was the replacement of wP by less efficacious aP vaccine and that an elevated level of pertussis would continue. The collapse in wP vaccine coverage in the 1970s and resultant outbreaks in the late 1970s and early 1980s could not explain the resurgence. Addition of an adolescent or toddler booster was predicted to have little impact on the disease in infants.ConclusionsOur findings support the recent recommendation by the World Health Organisation that countries currently using wP vaccine for primary immunisation should not change to aP vaccine unless additional strategies to control infant disease such as maternal immunisation can be assured. Improved pertussis vaccines that provide better protection against infection are needed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12916-016-0665-8) contains supplementary material, which is available to authorized users.

Highlights

In 2012 England and Wales experienced a resurgence of pertussis and an increase in infant deaths
We developed mathematical models to describe the pertussis transmission dynamics in England and Wales and to explore the following: the likely cause of the resurgence, in particular whether the change from whole cell pertussis (wP) to acellular pertussis (aP) vaccine or the decline in vaccine coverage in the 1970s and 1980s contributed to the resurgence; whether the higher incidence of disease in infants can be expected to continue; and the impact of the addition of a toddler or adolescent booster to the existing programme
Our results indicate that a continued higher incidence of pertussis in infants and older age groups can be expected in the future and suggest that the resurgence that began in 2012 reflects the resetting of incidence at a higher level when moving from the post-wP vaccine equilibrium to the post-aP vaccine equilibrium

Summary

Introduction

In 2012 England and Wales experienced a resurgence of pertussis and an increase in infant deaths. This occurred 8 years after acellular pertussis (aP) vaccine replaced whole cell (wP) primary vaccine despite continued high coverage for the primary series and pre-school aP booster. England and Wales, in common with several other countries, recently experienced a resurgence of pertussis despite sustained high vaccine coverage. The wP vaccination programme successfully reduced pertussis incidence until vaccine coverage collapsed in the 1970s and 1980s following publications that suggested a possible link between wP vaccine and brain damage (Fig. 1a and Additional file 1). The aP vaccine used exclusively in the UK until June 2014 was a five-component product (Pediacel®, Sanofi Pasteur MSD) containing pertussis toxin, filamentous haemagglutinin, pertactin and fimbrial antigens 2 and 3

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