IPD Serotypes Decreased 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 study data 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 the prepandemic levels that had been 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 study authors. “Many countries reported a decline in IPD cases, followed by an increase, coinciding with the relaxation of those measures.”

According to the authors, the unprecedented events and interventions throughout the pandemic significantly interfered with the dynamics of several infectious diseases and viruses. One of those is Streptococcus pneumoniae, the bacteria that causes IPD.

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

Due to stringent measures implemented during the pandemic, viruses such as S pneumoniae were less likely to spread, thanks to measures that included social distancing, mask-wearing, and staying at home. Findings from 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 2020-2021 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 controlled due to the development of pneumococcal conjugate vaccines (PCVs). In Portugal, where the current study was conducted, PCVs were first introduced in 2001 with a 7-valent version (PCV7). PCV13 eventually replaced PCV7 and was introduced into the country’s national immunization plan (NIP), leading to a 95% vaccine uptake.

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, researchers sought 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,” said 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 aged 18 or older.

Regarding the classification of serotypes that researchers were uncovering, those included in a previously developed pneumococcal vaccine were also 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 nonvaccine 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 during 2019-2020 and 2020-2021 but increased in the subsequent years: 542 in 2018-2019, 342 in 2019-2020, 127 in 2020-2021, 311 in 2021-2022, and 458 in 2022-2023. 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 more data relating to the COVID-19 pandemic are released, researchers often uncover 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.

As investigators explore the success of PCV development and serotype distribution, findings from studies such as this and previous ones underscore the importance of monitoring pneumococci isolates. As more vaccines are introduced, further 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

Don’t get left behind: Sign up today for our free Drug Topics newsletter and get the latest drug information, industry trends, and patient care tips delivered straight to your inbox.

REFERENCES

1. Guerreiro-Nunes A, Silva-Costa C, Gomes-Silva J, Ramirez M, Melo-Cristino J; Portuguese Group for the Study of Streptococcal Infections. The resilience of vaccine serotypes in adult invasive pneumococcal disease in Portugal, 2018–2023. Sci Rep. 2025;15(1):40146. doi: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;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