The battle against invasive pneumococcal disease (IPD) is far from over. Despite significant advancements in vaccines, a dramatic surge in cases between 2012 and 2024 underscores the urgent need for even more effective protection. This rise demands the development of higher-valent pneumococcal vaccines to combat the evolving threat of nonvaccine serotypes (NVTs).
Between 2012 and 2024, we've witnessed an alarming nearly 100% increase in IPD. This highlights the critical need for pneumococcal vaccines with broader coverage to protect against these NVTs. Even with the efficacy of the 20-valent pneumococcal conjugate vaccine (PCV20) and a stabilization of IPD potential from 2018 to 2023, research suggests that we need to go beyond PCV20, according to a study published in the Journal of Infection.
As the study authors noted, "To date, over 100 different pneumococcal serotypes with unique capsular polysaccharides have been identified with different ability to cause IPD." PCVs are effective in protecting against IPD caused by the serotypes they include.
IPD is a serious concern, especially for children, the elderly, and those with weakened immune systems. Caused by the Streptococcus pneumoniae (S. pneumoniae) bacteria, IPD can manifest as anything from a simple upper respiratory infection to severe conditions like pneumonia and meningitis. The introduction of PCVs in 2007 was a game-changer, leading to a massive drop in IPD rates among children. The CDC reported a 95% decrease in IPD cases among children under 5 and a 99% decrease for diseases caused by PCV13 serotypes between 1998 and 2001.
Early PCV formulations, like PCV7 and PCV13, have been superseded by higher-valent PCVs. In the US, PCVs are now more commonly used than the pneumococcal polysaccharide vaccine (PPSV). The current PCVs available in the US include PCV15, PCV20, and PCV21, the newest addition to the pneumococcal vaccine market.
"Worldwide, vaccine impact has been monitored through surveillance of pneumococcal carriage and IPD incidence," the authors continued. "Following the introduction of PCVs in national immunization programs (NIPs), shifts in serotype carriage and disease towards NVTs have been observed."
As IPD and S. pneumoniae colonization decreased, shifts in serotypes have increased the prevalence of NVTs—bacteria that the current PCVs don't protect against. To study these changes, researchers conducted a 20-year study in the Netherlands, analyzing higher-valent PCVs, serotype-specific carriage, IPD, and invasive disease potential.
Using data from the Dutch NIP, researchers examined two separate cohorts and compared their findings with data from carriage studies spanning 2005 to 2016. The cohorts were observed during the 2018-2019 and 2022-2023 winter seasons. All IPD data from children and adults covered the period from 2004 to 2024.
The analysis included a total of 331 patients in the 2018-2019 cohort (52% boys; average age 24.4 months) and 330 in the 2022-2023 group (53% boys; average age 24.1 months).
"Our data suggest an effective vaccination strategy, as evidenced by decreased and stabilized overall pneumococcal carriage rates and minimal detection of PCV10 serotypes in both carriage and IPD," they wrote. "Concurrently we observe serotype replacement, predominantly by NVTs and PCV20-specific serotypes. Serotypes from higher valent PCVs also show high invasive disease potential."
Pneumococcal carriage decreased throughout the study, dropping from 66% in 2005 to 49% in the 2018-2019 cohort and 46% in 2022-2023. Highlighting the success of PCV development and implementation, parents also saw a 15% decrease in carriage from 2005 to 2023.
But here's where it gets controversial... Despite these declines, IPD incidence increased among patients under 5 between 2018 and 2020, as well as 2022 and 2024. According to researchers, this recent rise in IPD among Dutch children is due to the 19A serotype.
Within the ongoing cycle of serotype distribution, which includes both PCV-specific serotypes and NVTs, researchers agree that higher-valent PCVs remain essential for national vaccine programs. Despite significant progress in reducing IPD rates in children, the evolving nature of serotype distribution will continue to drive the development of more PCV formulations.
"In conclusion, this study shows stabilized overall pneumococcal carriage between 2018-2023 with minimal invasive disease potential for the most frequently circulating serotypes," the authors concluded. "However, between 2012 and 2024 the overall IPD incidence nearly doubled and the relatively high invasive disease potential of NVTs highlight the need for implementation of a more-valent vaccine aimed at highly invasive NVTs."
What are your thoughts? Do you think the current vaccine strategies are sufficient, or do we need to accelerate the development of even broader-spectrum vaccines? Share your opinions in the comments below!
