IPD Serotypes Decrease Significantly During the COVID-19 Pandemic

Between 2018 and 2023 in Portugal, the number of serotype samples causing invasive pneumococcal disease (IPD) in adults decreased significantly, according to a study published in Scientific Reports.¹ Following a 76% reduction during the 5-year period, the number of samples has since increased but has not reached prepandemic levels—as what was seen among pediatric patients.

“Worldwide, the COVID-19 pandemic and the measures adopted to contain viral transmission had major impacts on other respiratory transmissible pathogens, including pneumococcal infections,” wrote the authors of the study. “Many countries reported a decline in IPD cases, followed by an increase, coinciding with the relaxation of those measures.”

According to them, the unprecedented events and interventions throughout the COVID-19 pandemic significantly interfered with the dynamics of several infectious diseases and viruses. One of those would be Streptococcus pneumoniae (S pneumoniae), the bacteria causing IPD.

READ MORE: Rise in IPD Calls for Development of More Pneumococcal Vaccines

Due to stringent measures during the pandemic, viruses like S. pneumoniae were less likely to spread because of measures regarding individuals’ social distancing, wearing of masks, staying at home, and more. A 2021 study in The Lancet Regional Health – Americas showed evidence of the pandemic’s impact on other respiratory viruses. According to the researchers, the 2020 to 2021 respiratory virus season was “effectively absent” in Canada, purportedly due to pandemic shutdowns.²

However, prior to the pandemic, the spread of S pneumoniae and its associated IPD-causing serotypes was relatively tamed because of the development of pneumococcal conjugate vaccines (PCVs). In Portugal, where the current study was conducted, PCVs were first introduced in 2001 with the 7-valent PCV (PCV7). PCV13 eventually replaced PCV7 and was introduced into the country’s national immunization plan (NIP), leading to a 95% vaccine uptake.

But despite these continuous vaccine developments to protect against S pneumoniae bacteria, IPD cases have still risen significantly, nearly doubling between 2012 and 2024.³

Amid continuous vaccine developments, changing serotype distribution, and a worldwide pandemic in between, researchers wanted to better understand the S pneumoniae patterns among Portuguese adults.

“We aimed to document serotype changes and antimicrobial susceptibility patterns among S. pneumoniae responsible for adult (≥ 18 years) IPD after almost 2 decades of PCV use in children,” continued the authors.¹ “Additionally, we wanted to evaluate the impact of the SARS-CoV-2 pandemic on the burden of disease and serotype distribution, as well as the potential coverage of the recently approved PCVs.”

Using data across 40 laboratories in Portugal, researchers collected bacterial isolates causing IPD from July 2018 to June 2023. IPD within the study design was defined as the isolation of S pneumoniae bacteria in normally sterile body fluid. Just 1 isolate from each patient was viable, and all patients included in the study were at least 18 years old.

Regarding the classification of serotypes researchers were uncovering, those that were included in a previously developed pneumococcal vaccine were included. Specifically, serotypes included in PCV7, PCV13, PCV15, PCV20, PCV21, and the 23-valent pneumococcal polysaccharide vaccine (PPSV23) were all classified separately. Those not appearing in PCV20 and PPSV23 were considered non-vaccine serotypes.

Their analysis yielded 1778 isolates causing adult IPD throughout the 5-year study period. The number of isolates distributed throughout each year of the study declined significantly from 2020 to 2021, but a rise began shortly thereafter. Indeed, the number of isolates went from 542 in 2018 to 2019 to 342 in 2019 to 2020, 127 in 2020 to 2021, 311 in 2021 to 2022, and 458 in 2022 to 2023. Pneumococci bacteria were most often recovered in patients’ blood (92.1%).

“As expected, there was a decrease in the number of isolates reported from adult IPD in 2019-2020 and 2020-2021, mirroring the situation found in children,” wrote the authors.¹ “However, although the number of isolates started to increase in 2021-2022, we have not reached prepandemic numbers, contrary to what was seen in the pediatric population.”

As a significant amount of research relating to the COVID-19 pandemic releases, researchers are often uncovering contradictory evidence containing unclear reasoning behind it. For example, the authors noted the potential for adults to continue pandemic health practices that helped stop the spread of SARS-CoV-2.

When exploring the success of PCV development and serotype distribution, studies like this—and those that came before it—continue to highlight the need for monitoring pneumococci isolates. As more vaccines are introduced, further expert attention will be necessary.

“Despite fluctuations in the number of episodes, serotypes 3 and 8 remain the leading IPD serotypes, although there were some changes throughout the study period. The increase in serotype 4, a PCV7 serotype rarer in previous years, should be closely monitored,” they concluded.¹ “The introduction of PCV20 in the NIP for children and in the national health authorities’ recommendations in 2025 will potentially further impact serotype distribution.”

READ MORE: Pneumococcal Resource Center

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REFERENCES

1. Guerreiro-Nunes A, Silva-Costa C, Gomes-Silva J, et al. The resilience of vaccine serotypes in adult invasive pneumococcal disease in Portugal, 2018–2023. Sci Rep 15, 40146 (2025). https://doi.org/10.1038/s41598-025-23819-w

2. Groves HE, Piché-Renaud PP, Peci A, et al. The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: a population-based study. Lancet Reg Health Am. 2021 Sep;1:100015. doi: 10.1016/j.lana.2021.100015.

3. Nowosielski B. Rise in IPD calls for development of more pneumococcal vaccines. Drug Topics. November 17, 2025. Accessed November 20, 2025. https://www.drugtopics.com/view/rise-in-ipd-calls-for-development-of-more-pneumococcal-vaccines