Cases of IGAS infections in children surged after decreasing early in the COVID-19 pandemic, which investigators attribute, in part, to reduced use of the protective measures imposed in the pandemic.
The trend emerging from the case series,1 drawn from 3 decades of population-based surveillance of IGAS in Southern Ontario, Canada, was marked by an increase in the emm1 strain, and associated rise in respiratory infections and ICU admissions.
The resurgence in incidence after the pandemic was, the investigators explain, "likely a result of an increased pool of nonimmune children, resulting from public health measures enacted to reduce SARS-CoV2 transmission also reducing GAS transmission, particularly of emm1 strains, during the pandemic.
"The postpandemic resurgence of viral respiratory infections, which are known to predispose to IGAS, also likely contributed to increased disease incidence," noted Halima Dabaja-Younis, MD, Infection Prevention and Control Unit, Sinai Health, Toronto, Ontario, Canada, and colleagues.
The investigators reported that IGAS incidence had declined from 2.4 events per 100,000 population per year in the period of 2012-2019 (incidence rate ratio, 1.3 [95% CI 1.1-1.6) to 1.2 in 2000 and 0.5 in 2021.Incidence then surged to 6.0 events per 100,000 population per year in 2023.
The most common strain in the surge was emm1 (182 of 471 isolates [38.6%]; followed by emm12 (15.9%), and emm4 (6.6%). Compared with other emm types, emm1 was more likely associated with pneumonia (odds ratio [OR] 1.99 [1.16-3.40]) bone and joint infections (OR 1.70 [1.08-2.68]) and ICU admission (OR 1.67 [1.03-2.68]}.
Dabaja-Younis and colleagues noted that while most of the emm types of the isolates (92.8%) were those that are included in the most current, advanced 30-valent GAS vaccine, this case series does not necessarily represent other populations.
"In populations in low- and middle-income countries, where strain distribution is different and diversity greater, other vaccines may be needed to provide adequate stain coverage," the investigators advised.
What You Need to Know
After declining during the early COVID-19 pandemic due to widespread non-pharmaceutical interventions (NPIs), IGAS infections in children surged significantly postpandemic. This increase is attributed to a larger population of nonimmune children and the easing of protective measures, which had also suppressed GAS transmission.
The resurgence was largely driven by the emm1 strain, which was the most common strain (38.6%) in the 2023 surge. This strain was notably associated with more severe outcomes, including higher rates of pneumonia, bone and joint infections, and ICU admissions.
While most detected strains (92.8%) are covered by the current 30-valent GAS vaccine, the strain diversity in lower-income countries may require different formulations. Experts also highlight that the observed surge reflects complex transmission dynamics and evolutionary pressures shaped by pandemic-era interventions, underscoring the need for ongoing surveillance and adaptive public health strategies.
Among other observations from the study was the temporal association of an increase in GAS pneumonia with the introduction of pneumococcal conjugate vaccine. Dabaja-Younis and colleagues consider possible factors for the interaction, including that changes in respiratory flora may have been a factor in the increase in GAS pneumonia.
In accompanying, invited commentary,2 Anthony Flores, MD, MPH, PhD, Division of Pediatric Infectious Diseases, Department of Pediatrics, Monroe Carell Jr Children's Hospital at Vanderbilt, Vanderbilt University Medical Center, Nashville, TN, suggests that the GAS emm types found prominent in the postpandemic surge indicate a more complex epidemiological shift than simple clonal expansion.
"Transmission bottlenecks play a critical role in shaping pathogen genetic diversity and evolutionary trajectories," Flores observed. "These bottlenecks, such as those implemented via NPIs (Non-Pharmaceutical Interventions, or personal protective measures) during the COVID-19 pandemic, may lead to divergence of a particular lineage from its broader genetic background due to restricted transmission pathways."
Flores emphasized the importance of elucidating these dynamics, not only to better anticipate the evolution of respiratory pathogens such as GAS, but for refining public health strategies for future outbreaks.
"We find ourselves in a critical stage in the intersection of politics, science, and public health," Flores declared."The postpandemic surges in GAS infections and our lack of understanding of the associated pathogen molecular changes should serve as a clarion call for renewed emphasis in active pathogen surveillance, the study of transmission dynamics, and pathogen emergence," he advised.
References
1. Dabaja-Younis H, Kandel C, Green K, et al. Invasive group A Streptococcal infection in children, 1992-2023. JAMA Netw Open. 2025; 8(4):e252861. doi:10.1001/jamanetworkopen.2025.2861.
2. Flores AR. Postpandemic surges proving the mettle of group A Streptococcus—Rising to the occasion.JAMA Netw Open. 2025; 8(4):e252872. doi:10.1001/jamanetworkopen.2025.2872.
