Strep throat infections during peak season have been running higher than pre-pandemic levels, and the surge isn’t random. A combination of weakened population immunity, more virulent bacterial strains, and a wave of viral co-infections has created conditions for strep to spread faster and hit harder than it did before 2020. Here’s what’s driving it.
Pandemic Lockdowns Left an Immunity Gap
The most widely cited explanation is something researchers call “immunity debt.” During the years of masking, social distancing, and school closures, people were exposed to far fewer circulating bacteria and viruses. That sounds like a good thing, but your immune system relies on regular low-level encounters with common pathogens to stay primed. For Group A Strep specifically, this matters more than it does for many other infections.
Unlike viruses such as measles, where a single infection or vaccine gives you long-lasting protection, strep defense depends heavily on a type of short-lived immune readiness called trained immunity. Your innate immune cells (the ones that respond first, before your body builds targeted antibodies) develop a kind of non-specific memory after repeated exposure to bacteria. But that memory fades quickly, typically within about three months if you’re not re-exposed. Two-plus years of reduced social mixing was more than enough to erase that population-wide protection.
The result: when restrictions lifted and strep began circulating freely again, it encountered a much larger pool of susceptible people, especially children who had missed the normal cycle of early childhood infections entirely. Invasive Group A Strep infections in children dropped to just 0.5 per 100,000 in 2021, then rocketed to 6.0 per 100,000 by 2023, a rate 2.5 times higher than the previous peak seen between 2012 and 2019.
A More Dangerous Strain Is Circulating
It’s not just that more people are getting strep. The strep they’re getting may be nastier. A sublineage called M1UK has been gaining ground, and it’s a more aggressive version of an already virulent strain family. M1UK produces significantly higher levels of a toxin called streptococcal pyrogenic exotoxin A, the same substance responsible for the rash in scarlet fever and for triggering the kind of extreme immune overreaction seen in toxic shock syndrome.
This strain picked up extra toxin-producing genes and a genetic mutation that cranks up toxin output compared to its predecessor, which had already been the dominant invasive strain worldwide since the 1980s. Because strains in this family are disproportionately linked to invasive infections (the kind that move beyond the throat into the bloodstream, muscles, or organs), any increase in their prevalence is a serious concern. In Europe, M1UK was identified as a major player in the 2022-2023 surge. Notably, the strain hasn’t developed increased antibiotic resistance, so it still responds to standard treatment. The problem is its ability to cause more severe illness, not that it’s harder to kill with medication.
Viral Infections Are Setting the Stage
The post-pandemic rebound didn’t just affect strep. RSV, influenza, and other respiratory viruses all surged simultaneously as immunity gaps converged across multiple pathogens. That overlap matters because viral infections can damage the lining of the throat and airways, making it easier for strep bacteria to invade deeper tissues. During 2022-2023, nearly a third of children with invasive strep infections (32%) had a viral respiratory co-infection at the same time.
Upper respiratory tract complications like severe pharyngitis and infections around the eye socket were significantly more common during that period than in any prior decade tracked by researchers. The pattern suggests that the combination of a virus weakening local defenses, followed by an aggressive strep strain encountering a child with limited prior immune training, is a recipe for unusually severe outcomes.
Children Are Being Hit Hardest
Group A Strep causes about 25% of sore throat cases in children, compared to a much smaller share in adults. Kids older than 5 and adolescents are the traditional high-risk group, with strep-positive rates between 19% and 30% of sore throats in that age range. But the recent surge has also shown up in younger children, and the severity numbers are concerning.
Among children with invasive strep infections during 2022-2023, over a quarter (26.8%) required intensive care, up from 17.7% across the full study period dating back to 1992. The case fatality rate for that two-year window was 5.4%, compared to the overall 30-year average of 2.0%. These are still relatively small numbers (56 children in the study’s 2022-2023 cohort), but the trend toward more severe outcomes in a post-pandemic environment is consistent with what public health agencies have been flagging.
Strep throat alone drives an estimated 5.2 million outpatient visits and 2.8 million antibiotic prescriptions per year in the U.S. among people under 65. During peak season, both minor and serious Group A Strep infections have been exceeding pre-pandemic levels. Low-season rates, by contrast, have returned to normal, which suggests the surge is concentrated during the winter and early spring months when strep has always been most active, just amplified.
An Antibiotic Shortage Made Things Worse
On top of the biological factors, a practical problem compounded the situation. In October 2022, the FDA declared a shortage of liquid amoxicillin suspension, the go-to antibiotic for young children who can’t swallow pills. Amoxicillin prescriptions for the liquid form dropped by nearly 31% almost immediately after the announcement.
Doctors adapted by shifting to alternatives. Non-suspension amoxicillin (tablets and capsules) prescriptions rose by about 8%, but a larger share of the gap was filled by broader-spectrum antibiotics: prescriptions for amoxicillin-clavulanic acid jumped 13.7%, cefdinir rose 6.4%, and cephalexin increased 3.4%. These drugs work, but they’re wider-acting than necessary for strep and raise concerns about promoting antibiotic resistance over time. For some families, the shortage also likely meant delays in starting treatment or extra trips to pharmacies, neither of which helps contain spread.
Is the Surge Winding Down?
There are signs the worst may be stabilizing. UK surveillance data for the 2024-2025 season shows both scarlet fever and invasive strep infections tracking within normal seasonal patterns, following the extraordinary spike of 2022-2023. The 2023-2024 season had already shown a return to more typical activity levels. In the U.S., the CDC continues to note that high-season strep numbers remain above pre-pandemic baselines, but the explosive year-over-year increases appear to have slowed.
The underlying drivers haven’t fully resolved. Population immunity is still rebuilding, the M1UK strain continues to circulate, and the expanded pool of asymptomatic strep carriers (people who harbor the bacteria without symptoms but can still transmit it) means the community reservoir remains larger than it was before 2020. What’s changed is that millions of people have now been re-exposed, gradually restoring the baseline level of immune readiness that keeps strep in check during normal years. Each season of circulation narrows the gap, but it may take several more years before the pattern fully resembles what existed before the pandemic disrupted it.