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Friday, July 12, 2024

Covid’s Summer Wave Is Rising—Again

It’s the summer tradition no one wants to partake in: Covid-19 cases are on the rise again. Hospitalizations from the virus ticked up in mid-July, increasing by 12 percent to just over 8,000 across the US for the week ending July 22. That’s nowhere near the pandemic peaks that overwhelmed health workers, but July brought the first weekly increases in hospitalizations since the US ended the federal Covid-19 public health emergency in May, just a week after the World Health Organization did the same with its global public health emergency.

The end of Covid-19 emergency status meant the US Centers for Disease Control and Prevention stopped tracking the virus as closely. But metrics show infections are still spreading. The pharmacy chain Walgreens reported a 42 percent positivity rate for tests during the last week of July, up from 29 percent in late June. And wastewater samples show concentrations of the virus moving upward across the country. Cases of Covid have also increased in Japan and the United Kingdom.

SARS-CoV-2 has spiked every summer since 2020. “There’s no reason that we wouldn’t see [a wave] this summer,” says Katelyn Jetelina, who writes the online health newsletter Your Local Epidemiologist. “We’re slowly but surely starting to see one summer wave and one winter wave.”

But experts have a hazier view of the building wave than in prior years. In the US, publication of hospitalization data comes a week behind the dates it captures. The CDC no longer tracks community levels of transmission. When the WHO emergency declaration was in effect, we saw more cross-government communication, but that’s less available now. “Our magnifying glass is a bit smudged compared to where we were a year ago,” says Josh Michaud, an associate director for global health policy at KFF, a nonprofit research group. “Many of the data points and indicators that we relied on in the past are no longer available to us.”

But there are still signs to watch. Wastewater testing, which can find traces of the virus expelled in feces, has shown a “sustained” increase in Covid-19 concentrations over several weeks, says Mariana Matus, CEO and cofounder of Biobot Analytics, a company that tracks Covid-19, Mpox, and opioids in US wastewater. The data from Biobot Analytics draws from about 600 wastewater data collection points and is valuable, Matus says, because it doesn’t exclude people who can’t afford testing or don’t report the results of at-home tests—and it can show the presence of Covid-19 in a community before large numbers of people get test results or are hospitalized.

But ensuring a bigger picture will require additional steps, such as expanding wastewater sampling. The decision to test wastewater largely relies on individual communities opting do their own testing. Matus imagines a more robust system that could help people make decisions based on pathogen concentrations in different regions, analogous to the Air Quality Index—data that could be easily displayed on something equivalent to a weather app. “We’re very excited about a vision and a future where people interact with wastewater data similar to how they interact with weather data, where it’s that pervasive in our society,” Matus says.

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At this point, it’s too early to say there’s a massive wave of infections building—but the hospitalization data is enough to pique the attention of epidemiologists and public health experts. Although case and hospitalization numbers are still relatively low, the virus does kill hundreds of people in the US each week. And as of early 2023, it had left an estimated one in 10 survivors fighting long Covid, which can include persistent health issues like breathlessness and brain fog.

There could be a few reasons for the current uptick in cases, waning immunity among them. Just around 17 percent of the US population has received bivalent vaccines, which became widely available in the fall of 2022 and are meant to offer better protection against Omicron variants. With lower case numbers over the past few months and many people not receiving a booster shot in 2023, immunity from vaccinations and prior infections could be decreasing, making more people susceptible to the virus, says Sam Scarpino, director of AI and life sciences at the Institute for Experiential AI at Northeastern University.

Experts guessed that Covid-19 would become seasonal, peaking in the fall and winter like the flu and the common cold, but other factors have kept the virus around in warmer months. “It’s true that you have cyclical patterns for most of these respiratory diseases,” Scarpino says. “I don’t think it’s really well understood what drives those.”

There could be some particular factors at play this year. Much of the US is enduring a suffocating summer. Wildfire smoke from Canada has engulfed the East Coast and Midwest, and exposure to the particulate pollution that comes with the smoke may weaken the immune system. Those were the findings of a 2021 study: In 2020, parts of California, Oregon, and Washington that experienced wildfire smoke saw excess Covid-19 cases and deaths. Meanwhile, dangerously high temperatures are keeping people indoors in the southern part of the US, and as a respiratory virus, SARS-CoV-2 spreads most easily indoors. People also traveled at record rates during the summer’s early months, which meant more opportunities for Covid to spread. But it’s not yet clear whether one, all, or none of these factors may be driving infections.

Genomic sequencing from the CDC shows that, as of June, offshoots of the Omicron variant are responsible for all of Covid-19 cases in the US. “On one hand, this is a good sign,” says Jetelina. “We can hopefully predict where SARS-CoV-2 is going.” That’s helpful for formulating updated coronavirus vaccinations. But it’s not certain that the virus’s evolution will continue down this Omicron path. In May, experts estimated the possibility of a highly mutated variant of concern arising during the next two years at about 20 percent.

In June, the US Food and Drug Administration recommended the development of an updated Covid-19 shot, preferring a formula that would target the XBB.1.5 Omicron variant. The FDA may authorize such a shot by the end of the month. But it’s hard to know whether people will be eager to get a fifth or sixth vaccine—pandemic fatigue, distrust of public health officials, and an overall return to normal life left many unenthused about last year’s booster and contributed to the low uptake rates. And while the US government previously bought doses directly and helped distribute them for free, the distribution of vaccines is now expected to move to the private sector.

Officials are unlikely to roll out wide-ranging restrictions on masking and social distancing—and barring a threatening new subvariant or a massive peak in cases, people are unlikely to change their behaviors after living alongside the virus for more than three years. It’s too soon to know whether the latest Covid-19 cases are a blip or a big wave. But as the dog days of summer linger, Covid is hanging around too.

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