In 2006, the UK introduced the 7-valent PCV (PCV7) into the infant immunization program with a 2+1 schedule, alongside a 12-month catch-up for all children up to 2 years of age. This program achieved a high vaccine coverage (>90%), resulting in a rapid and sustained reduction of Invasive Pneumococcal Disease (IPD) due to the PCV7 serotypes across all age groups. This impact was due to the direct protection from vaccination as well as indirect (herd immunity) protection achieved through the prevention of pneumococcal carriage in the vaccinated child’s nasopharynx and onward transmission to others. This decline was partially offset by small increases in non-PCV7 type IPD across all age groups.
In April 2010, PCV13 replaced PCV7, which led to further reductions in IPD due to the additional PCV13 serotypes. Since 2013/14 an increase in overall incidence of IPD has been observed, largely due to increases in non-PCV13 vaccine serotypes (especially serotypes 8, 12F and 9N) and mainly in older age groups.
In early 2020, the UK moved to a 1+1 infant schedule, with vaccinations given at 12 weeks and 1 year of age. Due to COVID-19 pandemic lockdown and subsequent restrictions since March 2020, IPD incidence decreased by 65% across all age groups in 2020/21 (see figure below). As restrictions were eased, IPD incidence gradually increased, initially in young children followed by older children and adults.
In 2022, PCV15, which protects against the PCV13 pneumococcal serotypes as well as serotypes 22F and 33F, was licensed for use from 6 weeks of age. UKs Joint Committee on Vaccination and Immunisation (JCVI) considered the use of PCV15 in a 1+1 schedule and agreed that the current evidence indicated it could be used in a 1+1 schedule. On the other hand, PCV20 which protects against 20 pneumococcal serotypes became available too but not yet included in UKs NIP.
Recent modeling suggests that PCV15 might increase overall invasive pneumococcal disease as the reduction in vaccine-type invasive pneumococcal disease would be counterbalanced by an increase in non-PCV15 invasive pneumococcal disease. By contrast, PCV20 is projected to have a substantial impact on overall invasive pneumococcal disease due to higher invasiveness of the additional serotypes covered by PCV20 than the replacing non-vaccine serotypes. Reduced carriage protection against PCV13 serotypes with higher valency vaccines would amplify these effects. (see PCVs table)
Replacing PCV13 with PCV20 is likely to have a substantial public health benefit, but PCV15 could potentially increase the overall burden of disease since it does not cover PCV20 STs
The decision to replace current PCVs with higher valency vaccines in pediatric vaccination programs requires careful evaluation, considering the complexity of the dynamic changes in pneumococcal transmission and the relative invasiveness of emerging serotypes in carriage. Multivalent vaccine formulations that preserve immunogenicity with increasing valency or the development of PCVs that complement existing PCVs by including only the main highly invasive non-vaccine serotypes could offer additional public health benefit.
Final Remarks
Adding more STs to PCVs decreases protein-polysaccharide conjugations, leading to decreased immunogenicity.
UK experience should be closely followed up to measure its impact and, in this way, evaluate if countries with similar epidemiology and PCV schedule history can switch to a shortened scheme such as the 1+1.
UK PCV Vaccines
References
- Green Book. Chapter 25. www.dh.gov.uk/greenbook.
- WHO. Pneumococcal conjugate vaccines in infants and children under 5 years of age: WHO position paper—February 2019. Feb 22, 2019. https://iris.who.int/bitstream/handle/10665/310968/ WER9408.pdf?sequence=1 (accessed on November 11th , 2024)
- Goldblatt D, Southern J, Andrews NJ, et al. Pneumococcal conjugate vaccine 13 delivered as one primary and one booster dose (1+1) compared with two primary doses and a booster (2+1) in UK infants: a multicentre, parallel group randomised controlled trial. Lancet Infect Dis 2018; 18: 171–79.
- Yoon Hong Choi, Marta Bertran, David J Litt, Shamez N Ladhani, Elizabeth Miller. Potential impact of replacing the 13-valent pneumococcal conjugate vaccine with 15-valent or 20-valent pneumococcal conjugate vaccine in the 1 + 1 infant schedule in England: a modelling study Lancet Public Health 2024; 9: e654–63
