If you’ve been noticing more of your friends posting photos of positive test sticks lately, it isn’t just your imagination. California is currently navigating a sharp, late-season wave that has caught many off guard. It’s a weirdly familiar feeling. Just when we thought we could breeze into fall without thinking about masks or boosters, the numbers started climbing. Honestly, the timing is kind of a mess.
By late August 2025, the California Department of Public Health (CDPH) reported that the state’s test positivity rate hit 12.07%. To put that in perspective, that is double what we were seeing just a month prior in July. In some spots, like Los Angeles County, the rate spiked even higher to 13.44%. We aren't just seeing a little bump; we’re seeing a significant "Stratus Summer" that has outpaced the transmission levels of the previous winter.
The Variants Driving the 2025 Surge
Why is this happening now? Basically, it’s a mix of biology and behavior. The primary culprit is a new subvariant dubbed XFG, or "Stratus." This thing is incredibly sticky. According to research from Stanford’s WastewaterSCAN program, Stratus has been the dominant strain in the Bay Area since July, accounting for over 80% of detected variants in sewage samples from San Francisco, San Jose, and Sacramento.
It’s not alone, though. We’re also seeing NB.1.8.1 (nicknamed "Nimbus") hanging around. Dr. Peter Chin-Hong, an infectious disease expert at UCSF, has noted that these variants are behaving a bit differently than what we saw back in 2020. They are way more transmissible, which means they find people easily, but for most healthy, vaccinated folks, the symptoms remain mild.
That said, "mild" is a relative term. Some people are reporting a "razor-blade" sore throat, heavy congestion, and even gastrointestinal issues that weren't as common with earlier Omicron subvariants. If you’ve got a "summer cold" right now, there is a very high statistical likelihood it's actually COVID-19.
✨ Don't miss: Why the Some Work All Play Podcast is the Only Running Content You Actually Need
Why Summer Surges are the New Normal
We used to think of respiratory viruses as "winter things." You get your flu shot in October, you hunker down in December, and you're good by May. But COVID-19 hasn't followed that script. It has maintained what experts call "dual seasonality."
- Heat Drives Us Indoors: When it’s 100°F in the Central Valley or a humid 85°F in SoCal, nobody is sitting on a patio. We’re all inside with the AC cranking, recirculating the same air.
- Waning Immunity: Most people got their last booster in the fall of 2024. By August 2025, that protection has significantly dipped.
- The Travel Factor: Summer 2025 saw massive travel numbers. People flying internationally or crowding into theme parks act as "super-spreaders" without even knowing it.
What the Wastewater Data Tells Us
Testing data is actually a bit unreliable these days because so many people use at-home kits and never report the results. That’s why public health officials are obsessed with poop. Wastewater monitoring is the most honest metric we have left.
Currently, wastewater viral activity levels in California are categorized as "High" by the CDC. In Los Angeles, Dr. Elizabeth Hudson from Kaiser Permanente Southern California noted that wastewater levels actually surpassed the peaks we saw last winter. It’s a sobering reminder that even if the hospitals aren't overflowing like they were in 2021, the virus is still everywhere.
The Hospitalization Reality
The good news? Death rates and ICU admissions aren't skyrocketing in tandem with the infection rate. As of late August, hospitalizations in California hovered around 3.62 per 100,000 people. While that number has doubled recently, it’s still considered "low" by historical standards.
🔗 Read more: Why the Long Head of the Tricep is the Secret to Huge Arms
However, pediatricians like Dr. Eric Ball in Orange County are sounding the alarm for the youngest Californians. Kids between 6 months and 2 years old are seeing hospitalization rates similar to seniors over 65. Because the vaccine rollout for this age group has been confusing and sometimes restricted, they are sitting ducks during this late summer surge.
Navigating the "Stratus" Wave: Actionable Advice
So, what are you supposed to do? We’re past the era of lockdowns, but that doesn't mean you should just ignore it.
Update Your Mask Game
If you're heading to a crowded concert or jumping on a flight at LAX, those flimsy blue surgical masks aren't going to cut it against the XFG variant. Use an N95 or KN95. Several counties, including Yolo, have officially recommended returning to indoor masking for high-risk settings.
The "Is it Jet Lag?" Test
If you just got back from a trip and feel "off," don't assume it's just the flight. Experts like Andy Pekosz from Johns Hopkins have pointed out how easy it is to mistake a mild COVID case for travel fatigue or a change in climate. Test immediately.
💡 You might also like: Why the Dead Bug Exercise Ball Routine is the Best Core Workout You Aren't Doing Right
Check the New Vaccine Schedule
The 2025-2026 COVID-19 vaccine is rolling out. If you haven't had a shot in over six months and you’re in a high-risk category (or live with someone who is), getting the updated formula is the best way to prevent a mild case from turning into Long COVID.
Monitor Your Symptoms
The "Stratus" variant is bringing more GI issues than previous waves. If you have a sudden onset of nausea or diarrhea alongside a scratchy throat, don't rule out COVID.
Practical Steps to Take Today:
- Restock your home test kits. Check the expiration dates on the ones in your medicine cabinet; many have likely expired by now.
- Improve ventilation. If the weather allows, crack the windows. If it's too hot, use HEPA air purifiers in common areas.
- Plan your booster. Reach out to your pharmacist to see when the 2025-2026 version is available in your zip code.
California's late summer surge is a reminder that the virus is opportunistic. It doesn't care that it's 90 degrees outside. Staying aware of the wastewater trends in your specific county and masking up in high-density indoor spaces are the most effective ways to make sure your summer finish doesn't end in a week of isolation.