Six years after the COVID-19 pandemic upended the world, experts in California say the disease appears to be becoming more of a summer rather than a winter phenomenon.
The shift was noted over the past couple of years and has become even clearer in 2026, prompting health officials to refocus their prevention efforts. The U.S. Centers for Disease Control and Prevention says COVID-19 is growing or likely growing in 43 states at the moment, including California.
California is also one of only four states where COVID wastewater activity levels are considered moderate or high, according to the CDC.
“Our summer peak was much higher in 2025 than it was in the winter,” Dr. Erica Pan, director of the California Department of Public Health and the state public health officer, said in a recent briefing. “Summer is really the bigger peak. So if you do have patients or loved ones who have not gotten the ’25-’26 vaccines, it is still effective and highly recommended, given this surge we’re starting to see.”
The pattern is also being seen nationally. COVID-related emergency department visits peaked last summer in late August, with COVID being responsible for 1.7% of visits. The winter peak was 1%. The trend was even more stark in California, peaking last summer at 2.1%, while there was not much of a winter peak at all, maxing out at around 0.2%.
This trend puts COVID in relatively rare territory as far as respiratory diseases go. Typically, those ailments — think flu and respiratory syncytial virus — spike in the winter, and aren’t really seen outside of that season.
In the early years of the pandemic, COVID spiked in both the summer and winter, with the winter waves being far more deadly. In 2021, for example, weekly COVID deaths spiked at more than 15,000 nationally around Labor Day, and peaked again at more than 21,000 in late January. Factors included people staying indoors due to the temperature outside, holiday travel and gatherings.
COVID deaths have dropped every year since then, but for a couple of years followed the two-peak pattern: a summer wave followed by a worse one in the winter. That has shifted in recent years, however, with doctors noticing the summer spikes were starting to get larger than their winter counterparts.
“It started in 2024. We started seeing a very large summer increase in cases and wastewater and hospitalizations, even dwarfing the winter. And then in 2025, that pattern continued, with more summer cases than winter cases,” said Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert.
It’s not entirely clear why recent summers have been more active for COVID than winters. And it’s not certain if that pattern will continue this year.
It could be that the summers of 2024 and 2025 happened to feature new coronavirus strains that spread quickly, like the FLiRT subvariant of 2024 and the Nimbus and Stratus subvariants of 2025, Chin-Hong said.
“This past fall and winter marked a change in how the COVID waves have been coming, with very little activity. The reasons for this are likely myriad, including that there was not a marked shift in the viral variant, plus the cumulative effect of people having both vaccine and natural immunity against COVID,” said Dr. Elizabeth Hudson, regional physician chief of infectious diseases at Kaiser Permanente Southern California. “We don’t have many updates on the variants coming from the CDC, so it’s possible we’re seeing this wave because there has been a change in the COVID variant.”
While COVID has become less of a public health threat since the early years of the pandemic, it can still be serious, even deadly. Those at higher risk should they get COVID are those who are older or immunocompromised, pregnant women and those who are younger than 5 years old, especially infants.
Infections also still present the risk of long COVID, a still relatively little-understood syndrome. People who get COVID also have been found to have an increased risk of stroke, heart attack and blood clots.
The rate at which coronavirus tests are coming back positive is increasing, as are viral levels in wastewater and COVID-related hospitalizations. Some doctors are now advising people to get vaccinated for COVID now if they haven’t received the most recent version of the vaccine.
The California Department of Public Health also says people age 65 and up, and those who are immunocompromised, should get a second COVID-19 vaccination six months after their first dose.
“Anyone who hasn’t received a 2025-26 dose, or is due for the second dose, is encouraged to get vaccinated now, before the next COVID-19 surge,” according to a slide in Pan’s presentation to health professionals.
“Disease is on the rise in California, where we’re seeing increasing cases, increasing test positivity, increasing in our wastewater. This is a good time, actually, to protect yourselves or your family,” Pan told The Times in an interview, “because we anticipate, based on the last couple of years at least, that that this may be the larger peak than the winter.”
Some may find it hard to get the 2025-26 version of the COVID vaccine, however. Kaiser no longer offers that version of the vaccine, but expects the 2026-27 version to be available by late September.
“In terms of whether to get the 2025-2026 COVID vaccine, if you did not get one last winter, you can get one now, if your clinician still has them available. However, if you want to wait to get the newest one, given how soon it will be available, it’s very reasonable to wait,” Hudson said.
Chin-Hong said it was particularly important to get the shot now for those at higher risk of becoming seriously sick from COVID, who haven’t been vaccinated in more than a year. He said the COVID patients who need to be seen in the hospital are generally higher-risk individuals with vaccinations that are not up to date.
Particularly for those who are older and immunocompromised, “go and get the shot now,” Chin-Hong said, “especially when we’re seeing that summer is the new winter in the last two years in California. Don’t wait for the fall.”
Severe illness, hospitalization and death from COVID “is preventable” with vaccination, Chin-Hong said. State health officials forecast a moderate increase in COVID hospital admissions later this summer and in early fall.
The California Department of Public Health recommends the 2025-26 COVID-19 vaccine for seniors age 65 and up, those age 6 months to 23 months, pregnant women, anyone with risk factors and those in contact with them, children and teens never vaccinated against COVID, and anyone else who chooses to be vaccinated.
For now, the most recent data show that levels of coronavirus in sewage are a fraction of last summer’s peak. But the test positivity rate in the San Francisco Bay Area is now considered moderate, with 7% of conducted tests coming back positive for the week that ended Aug. 1, up from 2.7% a month earlier, according to data from the California Department of Public Health.
The Los Angeles County Department of Public Health said its COVID test positivity rate for the week that ended Aug. 1 was 4.25% — up from 2% a month earlier, but still considered low.
Orange County’s rate was 6.5%, up from 2.4%. In Northern California’s most-populous county, Santa Clara, COVID levels are high in the area’s sewersheds, according to that county’s Public Health Department.
COVID hospitalizations in California are rising, but remain lower than they were for the past two summers. California most recently reported a rate of 0.84 hospitalizations for every 100,000 residents; a year ago, the rate was 1.92; and the year before that, it was 8.12 .
However, while the disease’s wider risk has waned, it has not vanished. For the 2025 calendar year, 20,685 deaths were attributed across the nation to COVID-19 on death certificates, according to the CDC. There were 47,541 deaths in 2024; 76,055 in 2023; 247,168 in 2022; 463,267 in 2021; and 385,676 in 2020.
In California, there were 1,813 deaths involving COVID-19 in 2025. The statewide death toll was 4,219 in 2024; 6,989 in 2023; 22,713 in 2022; 48,333 in 2021; and 33,579 in 2020.
The Food and Drug Administration earlier this month approved its first flu shot using mRNA technology — the same employed to make the two most widely used COVID vaccines. The new flu vaccine, manufactured by Moderna, is called mFLUSIVA and made for adults age 50 and up.
The vaccine was considered fully approved for those ages 50 to 64. For those who are at least 65 years old, the vaccine was given what the FDA calls “accelerated approval,” which requires additional verification and evidence of a clinical benefit in a confirmatory trial, according to the company.
In studies, mFLUSIVA was compared to standard-dose vaccines, but not the various kinds of turbocharged flu shots that have been made available for years for seniors, according to Pan. Those include versions that are considered higher dose or “adjuvanted,” which helps trigger a stronger immune response.
A benefit to the approval of an mRNA flu shot is that, in future seasons where a new strain suddenly emerges, vaccine manufacturers will be able to more quickly release new shots to combat it. During the 2009 H1N1 “swine” flu pandemic, getting newly formulated shots “took a lot longer than we hoped,” Pan said.
That flu pandemic strain emerged in the spring of 2009, but a specially formulated vaccine only became available in large quantities in late November, “after the peak of illness during the second wave had come and gone in the United States,” according to the CDC. That pandemic hit children and younger and middle-aged adults harder than seniors, who likely had been exposed to an older version of the H1N1 virus when they were younger.
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