The PCV is a conjugate vaccine (see our page on 'Types of vaccine'). Sugars (polysaccharides) are taken from the capsule around the pneumococcal bacteria and joined to a non-toxic diphtheria protein called CRM197. The protein helps to stimulate the immune system in a broader way to respond well to the vaccine. This gives a better immune response in individuals of all ages.
In recent years, there have been several changes to the pneumococcal vaccination schedule in the UK:
- 2002: a pneumococcal conjugate vaccine protecting against 7 types of pnemococcal bacteria (PCV7) was recommended for
immunisation of babies and children in at-risk groups under the age of two years
- 2003: pneumococcal polysaccharide (PPV) immunisation was recommended for all people aged 65 and over
- 2004: PCV7 was extended to at-risk babies and children under five years of age
- 2006: PCV7 was added to the routine childhood immunisation programme
- 2010: a pneumococcal conjugate vaccine protecting against 13 types of pnemococcal bacteria (PCV13) replaced PCV7.
How well does the vaccine work?
It is estimated that in the first 11 years of the pneumococcal vaccine programme (2006-07 to 2016-17), the vaccine prevented nearly 40,000 cases of invasive pneumococcal disease, and about 2000 deaths.
The original version of the PCV (Prevenar7) was introduced in 2006. This vaccine protected against seven of the types of bacteria, and resulted in a big reduction in the number of cases of pneumococcal disease in babies caused by these seven types. However, there was an increase in the number of cases caused by other types of pneumococcal bacteria. Six strains in particular were identified as causing most of the new cases of pneumococcal disease.
In 2010, the PCV vaccine was changed to one that protected against 13 types of bacteria (Prevenar13). Research in 2011 by the UK's Health Protection Agency (now Public Health England) showed a big reduction in serious disease caused by the additional six types of pneumococcal bacteria protected against by the new vaccine. Another study by Public Health England published in 2015 confirmed that 8 years of PCV use in England and Wales had reduced the overall incidence of invasive pneumococcal disease by more than 50%. The PCV has a herd immunity effect. Vaccination of babies has reduced the amount of disease in the whole population, because infants and children are no longer carrying so many pneumococcal bacteria and spreading them around.
However, the 2015 research noted that other strains of pneumococcal bacteria were starting to become more common, and could partly replace the strains that are disappearing, especially in non-vaccinated older individuals. Public Health England has continued to monitor this trend. It has found that strains not covered by the PCV have increased, and are causing more cases of pneumococcal disease (over 4000 cases in 2015-16, compared with about 2000 cases in 2010-11). Recent reports can be found here .
At the moment the disease caused by these strains is generally less severe and less likely to be fatal. There is still a very substantial reduction in disease in young children but non-vaccine strains have replaced the reductions in disease in older age groups to some extent. Public Health England is continuing to monitor the situation. Future strategies might include development of vaccines for a wider set of pneumococcal bacteria, especially for those causing replacement disease in the elderly.