Editor's Note: Dr. Claire Castellano (she/her/hers) is a resident physician in pediatrics at the Children’s Hospital of Philadelphia. In addition to her MD, Claire has a Master’s in Public Health, focusing on global epidemiology. Claire hopes to combine her interests in medical education and global health in her career as a pediatrician. – Rachel Y. Moon, MD, Associate Editor, Digital Media, Pediatrics
Vaccinations are a crucial part of any pediatrician’s practice. The world of immunizations has been in the spotlight recently, with the new COVID-19 messenger RNA (mRNA) and monoclonal respiratory syncytial virus (RSV) antibody shots making a splash in the news.
But what about the mainstay vaccinations that are part of any child’s standard immunization schedule? Some of them have updates, too!
Dr. Inci Yildirim, from Yale University, and colleagues share how changes to the pneumococcal conjugate vaccines (PCV) have influenced the rates of invasive pneumococcal disease (IPD) in their article, “Invasive Pneumococcal Disease After Two Decades of Pneumococcal Conjugate Vaccine Use,” being released early this week in Pediatrics (10.1542/peds.2023-063039). (We want to disclose that 3 of the authors are employees and shareholders of Pfizer Inc., which manufactures PCV, and that Pfizer provided funding for this study.)
In 2000, the first generation of PCV, the 7-valent or PCV7, was introduced in the US. It protected against 7 serotypes (types) of pneumococcus: serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. Ten years later in 2010, the 13-valent, PCV13, became the new standard of care. It added 6 additional serotypes: 1, 3, 5, 6A, 7F, and 19A. In this study, the authors analyzed surveillance data for cases of invasive Streptococcal pneumoniae disease (IPD), defined as bacteremia, pneumonia, or meningitis, among children <18 years of age living in Massachusetts from 2002 to 2021.
In general, the vaccine works—really well! The incidence of IPD decreased by 72% between 2002 and 2021, and this rate of decline improved even more when PCV13 replaced PCV7. The reduction in IPD rate is serotype-specific, meaning there are fewer cases of pneumococcal disease from the specific serotypes the vaccines are targeting.
But what about the children who are still getting IPD? Who are they and where are these cases coming from? The authors classify them into two main buckets:
- Cases caused by pneumococcal serotypes that are included in the vaccine.
- Cases caused by pneumococcal serotypes that were never included in the vaccine.
Their results are as follows:
- In the PCV7 era (2002–2010), nearly 60% of all IPD cases were from 3 serotypes (3, 7F, and 19A), all of which were subsequently included in PCV13.
- In the PCV13 era (2010–2021), IPD cases were largely from serotype 3 and serotypes not included in PCV13.
- Serotype 3 remains responsible for many breakthrough IPD cases, or IPD in children who were sufficiently immunized by PCV.
- Children with chronic medical conditions, such as neuromuscular, pulmonary, cardiac, and immune-compromising diseases, remained at increased risk for IPD, both before and after the implementation of PCV-13, consistently accounting for approximately 25% of all IPD cases.
- From May 2020 to June 2021, or during the peak of the COVID pandemic, incidence of IPD was at an all-time low.
How can this data translate to patient care and inform goals for future work?
- Future Vaccines: Knowing which serotypes are causing disease by doing surveillance studies such as this one is important for future vaccine development. For example, the non-PCV13 serotypes that have made up many cases of IPD in the PCV13 era should be considered as ones that should be included in future versions of PCV.
- Serotype 3: Although this serotype was included in both PCV7 and PCV13, it still contributed to a large proportion of breakthrough infections. Future studies should try to understand why there were so many breakthrough infections.
- Vulnerable Populations: The medical conditions that placed children at increased risk for IPD were all common, with asthma, prematurity, and neuromuscular disorders as the most prevalent, highlighting the importance of vaccination efforts in these populations. The authors speculate this may be due to these children’s chronic inflammatory status, but there is a need to better understand why they are at such risk.
Newer iterations of PCV, such as PCV15 and PCV20, are now being distributed. It will be important to continue to track serotype information to further optimize vaccines, which will ultimately result in fewer invasive diseases in children.
