Why COVID keeps roaring back every summer?

By many measures, the coronavirus is a thing of the past. Masks have been stored away. Social distancing is just a vague memory. Interest in vaccines is waning. COVID, for many, feels like an inevitable annoyance, like the flu. Then, each summer, we get a rude reminder.

The season of travel and fun continues to bring a spike in COVID-19 activity, far less profound than during the height of the pandemic but enough for people to notice and worry. This summer's jump is being fueled by the subvariant XFG, nicknamed "Stratus."

"As we learn more about COVID, we are seeing that it has two surges a year: the late fall/early winter and in the summer, so we expect this trend of increased cases in the summer to continue," said Dr. Elizabeth Hudson, the regional chief of infectious disease at Kaiser Permanente Southern California.

Why summer? There are a number of factors that could explain why COVID activity seems to ramp up along with the temperature, according to the Los Angeles County Department of Public Health:

• Summertime travel and increased social mixing because of social events.

• Spending time indoors to beat the heat: Respiratory viruses tend to spread more easily in environments with low humidity and cool temperatures. Air-conditioned spaces might not have adequate ventilation.

• Waning immunity from vaccination and previous infections.

• Mutations: As the virus spreads, it acquires mutations that allow it to evade our existing immunity. Eventually, a version of the virus collects enough mutations that it has a slight edge over other viruses, and if other factors line up, it can sweep through a population.

What do the numbers show? The rate at which coronavirus tests in California came back positive was 11.59% for the week ending Aug. 16. That's up from a positive test rate of 5.69% for the week ending July 19, according to the California Department of Public Health. The positive test rate is expected to further increase in the coming weeks, the department said. "COVID-19 test positivity this summer looks similar to (the) summer of 2023 so far," the department said. That year saw the summer COVID wave peak in early September.

Last year, which saw the largest summer spike since 2022, COVID activity maxed out in early August. COVID is also increasingly a reason why people are seeking urgent medical care. For the week ending Aug. 17, COVID diagnosis was the reason why 4.04% of children in California up to age 11 were in the emergency room — up from 1.02% during the last week in June. COVID was the reason why 2.25% of people age 75 and older were in the emergency room over the same period, up from 1.13% during the last week of June, state data show.

So what? The pandemic emergency is over. The rise in COVID comes as the disease has receded as a major worry from the minds of many, with fewer people getting annual COVID vaccines and even fewer wearing masks in any setting. Still, COVID can result in significant illness — a "razor blade" sore throat and miserable cough for some and hospitalisation and even death for the very young, very old and chronically ill. The US Centers for Disease Control and Prevention estimates that at least 38,000 have died from COVID-19 for the season that began Oct. 1. During the same period, the CDC estimates the number of flu deaths to be at least 27,000.

What are the vaccine numbers like? Just 14.7% of California's population has received the updated COVID-19 vaccine that first became available nearly a year ago. Uptake was greatest among the oldest Californians, with 37.2% of state seniors age 65 and up getting the vaccine. For those ages 50 to 64, 17.7% have gotten their shot, as have 9.5% of younger adults ages 18 to 49. Among children ages 5 to 11, 5.9% have been vaccinated, and for those younger than 5, 3.2% have been vaccinated with the latest COVID-19 vaccine formula. The California Department of Public Health continues to recommend that everyone age 6 months and older stay up to date on their COVID-19 vaccinations. "This is particularly important for higher-risk individuals, such as infants and toddlers, pregnant individuals, older persons, and others with risks for serious disease," the department said.

The department's advice resembles the CDC's past guidance, which has changed since the start of the second Trump administration and the appointment of vaccine skeptic Robert F. Kennedy Jr. to head the CDC's parent agency, the Department of Health and Human Services. The CDC now says it offers "no guidance" as to whether healthy pregnant women should get the COVID vaccine, and asks parents of healthy children to talk with a healthcare provider before getting the COVID vaccine for their youngsters. Mainstream medical organisations, like the American College of Obstetricians and Gynecologists, continue to recommend that people receive the updated COVID-19 vaccine at any point during pregnancy. The American Academy of Pediatrics recommends infants and children ages 6 months to 23 months get the updated COVID vaccine, since they are at high risk of severe illness should they get COVID, and that the vaccine should be offered for children age 2 and older if their parent wishes.

Some doctors, including Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert, have suggested that people who haven't been vaccinated in more than a year, and are at risk for severe complications should they get COVID, get vaccinated with the currently available shots now. Chin-Hong noted that the 2025-26 version of the COVID vaccine should be "relatively the same formula" as the 2024-25 version. "It's less important to wait," he said. Eligibility for the new vaccine has been delayed by the Trump administration, and it isn't clear when it'll become available or who will be eligible outside of older people and those with chronic health conditions.

Some pharmacy chains and health providers have paused online scheduling of appointments for COVID-19 vaccines until the 2025-26 version is released, presumably later this year. But at least one chain, CVS, says all of its pharmacies nationwide offer the 2024-25 version of the COVID-19 vaccine and that it is available on a walk-in basis. "All CVS Pharmacy locations across the U.S. currently offer the COVID-19 vaccine. We'll continue to offer to eligible patients, as determined by the [Food and Drug Administration] and CDC, until an updated 2025-2026 vaccine is released," CVS spokesperson Amy Thibault said in a statement to The Times. "Digital vaccination scheduling is paused temporarily, but we are still offering walk-in COVID-19 vaccinations," Thibault said.

What might the rest of the summer look like? Officials note that the spread of COVID appears to be less severe this summer compared to last. Across California, levels of the coronavirus detected in wastewater are about 20% lower than the peak of the 2023 summer wave, and about 50% below the height of the 2024 summer wave, the state Department of Public Health said. For this time of year, COVID hospitalizations are currently considered low, based off thresholds "established from the data from the past five seasons," the department said. "Deaths are also lower than previous seasons."