Impact of pneumococcal conjugate vaccine on pneumococcal disease prevalence and genetics in the UK

Monitoring the effect of pneumococcal vaccine

Scientific version
  • Researchers:
    Dr Bruno Pichon, Dr Mary Slack, Dr Rob George, Prof Liz Miller
  • Start Date:
    01 March 2007
  • Category:
    Prevention, Surveillance
  • Location:
    HPA Centre for Infections, London, UK
Impact of pneumococcal conjugate vaccine on pneumococcal disease prevalence and genetics in the UK

What was this project about?
The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced into the routine UK infant immunisation programme in 2006. PCV7 protects against 7 of the most common types (out of the 92 actually known) of the pneumococcus, at the time the most common causes of bacterial meningitis and pneumonia in both children and adults. Ongoing surveillance carried out by Health Protection Agency suggested that the immediate success of the PCV7 programme may have been compromised by an increase of pneumococcal disease (including meningitis) caused by types of pneumococci not covered by PCV7.

What were the original aims?

This project set out to assess the long term impact of PCV7 vaccination on the types of pneumococcal bacteria circulating in the UK and causing meningitis. It also looked at the ways in which the pneumococcal bacteria change in response to introduction of a vaccine.

What were the study results and why are they important?

Genetic characterisation of some of the pneumococci causing meningitis revealed that

  • the disease is caused by genetically diverse bacteria and
  • the number of cases due to non vaccine preventable pneumococci has increased since the introduction of the vaccine suggesting that the non vaccine preventable clones are gradually replacing the vaccine preventable pneumococci.

On some occasions bacteria have changed their outer coating allowing the pathogen to escape the vaccine. However so far this phenomenon is rare in the UK which contrasts markedly with the situation in the US where pneumococci escaping the vaccine expanded in the population.

In older age groups, the expected immune herd effect occurred, reducing the number of pneumococcal disease (IPD) caused by pneumococci covered by PCV7.

Antibiotic resistance is an increasing problem for the treatment of pneumococcal diseases, particularly meningitis. Genetic analyses of pneumococci with reduced susceptibility to certain antibiotics suggest that the mechanisms involved were diverse. Further research and analysis is needed in order to determine the longer term impact of PCV7 on pneumococcal antibiotic resistance in UK.

The success of PCV7 has been compromised to some extent by rapid serotype replacement where bacteria not covered by the vaccine start to cause more disease. The introduction of PCV13 (covering 13 types of pneumococci) in April 2010 which would have prevented 54% of invasive disease in 2008/09 may be similarly compromised by expansion of other pneumococci which are not targeted by any of the available pneumococcal vaccines. Continued surveillance of IPD is therefore essential. It is anticipated that the data generated will help to inform future pneumococcal vaccine policy.

Publications

The results from this project have been published in several scientific journals:

Molecular Typing of Pneumococci for Investigation of Linked Cases of Invasive Pneumococcal Disease
J Clin Microbiol 2010 May; 48(5): 1926–1928

Changes in the molecular epidemiology of Streptococcus pneumoniae causing meningitis following the introduction of pneumococcal conjugate vaccination in England and Wales
J Clin Microbiol 2013 Mar;51(3):820-7