Epidemiology

Before the introduction of pertussis immunisation in the 1950s, the average annual number of notifications exceeded 120,000 in the UK. By 1972, when vaccine coverage was around 80%, there were only 2069 notifications of pertussis.

• Two major epidemics occurred in 1977-79 and 1981-83 due to a report published which suggested a possible link between the vaccine and brain damage (which resulted in immunisation coverage dropping to 30%).
• Since the mid-1990s, coverage has been consistently over 90% by the second birthday has exceeded 95% since 2009/10 (1).

Despite sustained levels of vaccine coverage above 95% from 2010, an increase in pertussis activity was observed in England and Wales from October 2011 and continued into 2012 (2):

• initially affecting adolescents and adults and later extending to young infants
• national outbreak was declared in April 2012

Despite the current low levels of disease, pertussis in the very young remains a significant cause of illness and death (1).

• Highest incidence of the disease is seen in infants less than 3 months - laboratory confirmed pertussis: 77 per 100,000 population in 2015 (2).
• Young infants are at highest risk of severe complications, hospitalisation and death (3).

In response to this outbreak, in October 2012, the Department of Health introduced a temporary programmed to offer pertussis vaccination to pregnant women ideally between 28-31 weeks (but up to 38 weeks) of their pregnancy (1,2).

• In February 2016, JCVI (Joint Committee on Vaccination and Immunisation) advised that maternal pertussis immunisation can take place from week 16 of pregnancy (1).

Note:

• resurgence in disease in the presence of sustained high vaccine coverage may potentially be explained by improved case ascertainment, change from whole-cell to acellular vaccines, waning immunity, and genetic changes in B. pertussis (1)

Reference:

• (1) Immunisation Against Infectious Disease - "The Green Book". Chapter 24. Pertussis (April 2016)
• (2) Public Health England (PHE) 2018. Guidelines for the Public Health Management of Pertussis in England
• (3) Public Health England (PHE). Pertussis brief for healthcare professionals