The US has a new Covid-19 strain on the rise. Meet Eris.

In the latest data published by the Centers for Disease Control and Prevention (CDC), Covid-19 hospitalizations rose 12.5 percent between July 23 and July 29. Overall, they have been increasing since July 1.

And in the last week, there was a 10 percent increase in locations reporting their highest levels of SARS-CoV-2 ever in sewage wastewater (and that’s despite a decrease in the number of cities reporting the virus in their wastewater).

This is all to say: Covid-19 appears to be making a comeback. And what’s more, this summer uptick coincides with (but may not be caused by) a new dominant strain of the virus taking hold in the US. It’s called EG.5, unofficially nicknamed Eris, and the CDC estimates it’s causing 17.3 percent of current Covid-19 cases in the country. And it’s on the rise: Since the beginning of July, EG.5’s prevalence has increased 9.8 percent.

The EG.5 variant descended from the omicron variant, which caused an explosive outbreak in late 2021 and early 2022. On Wednesday, the World Health Organization (WHO) upgraded EG.5 from a variant “under monitoring” to one of “interest,” meaning it believes it could pose an “increased risk to global public health.”

“Based on its genetic features, immune escape characteristics, and growth rate estimates, EG.5 may spread globally and contribute to a surge in case incidence,” WHO’s EG.5 Initial Risk Evaluation report states. “Several countries with rising EG.5 prevalence have seen increases in cases and hospitalizations, although at present there is no evidence of an increase in disease severity directly associated with EG.5.”

Infectious disease experts tell Vox they agree the new variant is worth paying attention to, but are cautious in saying how concerned we should be.

“Although the EG.5 variant apparently has a slight competitive advantage [over other strains] — and we’ve seen the number of cases go up slightly and the number of hospitalizations go up slightly — I don’t think there’s any reason to expect a massive wave like we saw with omicron,” said Rebecca Wurtz, an infectious disease physician and a professor of health policy and management at the University of Minnesota School of Public Health.

A new Covid-19 variant understandably puts a country ravaged by the virus on edge, but compared to the last three summers, Covid-19’s impact on the health care system in the US remains low.

As of now, if people keep up with prevention efforts, they should be able to stay safe, Ruth McDermott-Levy, a professor at the Louise Fitzpatrick College of Nursing at Villanova University, told Vox.

“I think we should be a little more alert,” McDermott-Levy said of the new variant. There are several reasons it’s unlikely to cause as bad of an outbreak as past variants. “But I think continue to be vigilant and pay attention.”

How severe and contagious is EG.5?

The symptoms of EG.5 don’t appear to differ much from other omicron subvariants. Infected individuals report cough, fever, chills, shortness of breath, fatigue, body aches, loss of taste or smell, and headaches, among other symptoms.

The WHO reports that EG.5 is not resulting in more cases or deaths than its predecessor, the XBB strain of omicron.

But it’s possibly more contagious than other strains.

“The fact that [EG.5] is emerging quickly suggests that it does have some slight competitive advantage,” said Wurtz. This advantage is likely that it’s slightly more contagious or more capable of evading existing immunity, but, she added, more data is needed to confirm.

The good news is that this strain likely won’t cause as big of a wave as past variants, said Maureen Miller, an epidemiologist with the Columbia University Mailman School of Public Health. That’s because there’s more widespread immunity to SARS-CoV-2 either from vaccines or natural infection. But still, not everyone is equally protected, depending on when they were last vaccinated or exposed. “The bad news is that these protections wane,” she added. Given winter waves of Covid-19 have historically been the largest, it’s vital that people check to see if they are up-to-date with their boosters.

The hurdles to understanding EG.5

While EG.5 does not appear to make people more ill, the reason for its prominence remains a mystery. Scientists do have genetic sequence data on EG.5 and have zeroed in on some of the mutations that set it apart from past variants, but they don’t know “exactly why this mutation confers an advantage,” Wurtz said.

One hurdle to understanding EG.5’s reach is the fact that there’s less outbreak data than earlier in the pandemic. As of August 8, the CDC only published NowCast estimates of the proportion of Covid-19 variants in areas in New York and the western and southeastern US. In the past (even as recently as early July), data was available for much of the US.

“As of May 11, the emergency response to Covid was lifted and that reduces funding” for the pandemic response, said McDermott-Levy. She noted that an increase in at-home testing could be contributing to the under-reporting. Also, she says, people might just be “tired” of Covid and therefore aren’t reporting cases. “But we’re reminded it’s not going to go away just because we’re tired of it.”

Thankfully, we’re not totally in the dark. The US has adopted some new approaches to understanding emerging strains, and “we have wastewater monitoring, which is a fantastic way to get a nonvoluntary, at-home sample of the entire population,” said Wurtz.

Wastewater surveillance involves states, cities, and tribal health departments testing wastewater for the presence and prevalence of the Covid-19 virus and reporting this data to the CDC. Despite some variance, overall there has been a rise in the areas reporting increasing rates of Covid-19 in their wastewater since early June.

How to protect yourself

Across the country, people have started returning to pre-pandemic ways, but McDermott-Levy, who is currently recovering from a Covid-19 infection she got from a family gathering, says the current upswing in cases is a reminder that we need to remain cautious.

“In retrospect, for my own case, I would have asked family members to test before they came. I used to do that,” she said. She also recommends practicing health habits, such as giving up smoking, to ensure your immune system is as strong as possible in case of infection.

All of the same Covid-19 prevention methods still apply. And the same groups are at highest risk for severe infection; older adults, those with compromised immune systems, and those with chronic diseases, said Miller.

People should wear an N-95 mask, social distance when possible in public spaces, and keep up-to-date on vaccines and boosters. Soon, a new Covid-19 vaccine formula will be available. It’s specifically designed to protect against the XBB subvariants (EG.5 descends from XBB) and will hopefully work to reduce the severity of EG.5 infections, said McDermott-Levy.

These shots are especially important given the upcoming back-to-school and winter seasons. There is an under-discussed seasonality to Covid-19 infections that lines up with weather patterns, said Miller. “When it’s too cold outside, people are inside. When it’s too hot outside, people are inside,” she said. Because the virus thrives in spaces where people are in close proximity, this is a problem.

Unfortunately, EG.5 and other future variants are merely a piece of the post-Covid world, but we do have the technology needed to track the virus’s rapid evolution. And that’s helpful, despite there being less data on Covid-19 cases overall.

“It’s important to pay attention, but also not to get extremely worried about each new variant,” said Wurtz. “This is the way it’s going to be and always has been with viruses, but we just didn’t have the ability to track [the genetics] the way we do now.”

Scientists will learn more about this variant. In the meantime, being a little more Covid-vigilant can help.

Update, August 9, 12:40 pm ET: This story was originally published the morning of August 9 and has been updated to reflect the WHO’s new classification for EG.5.