EAU CLAIRE — Wisconsin still has found relatively few cases of the fast-spreading Delta variant of COVID-19, but experts and studies suggest that if the strain finds a firmer foothold in the U.S. in coming weeks, it may spread more quickly among people who aren’t vaccinated.

Seventy-one cases of the Delta variant have been identified in Wisconsin, as of Thursday.

The real number of Delta variant cases is almost certainly higher, the state Department of Health Services has warned, since only a fraction of positive COVID-19 specimens undergo lab testing to detect if they’re caused by variants — a process called whole genome sequencing.

The new, more transmissible Delta strain has caused big ripples overseas, though it’s not clear yet if it causes more severe illness in infected people. The Delta variant drove a massive case surge in India this winter and spring. Cases in Britain are doubling every nine days, and the country has postponed lifting virus restrictions. In the United States, roughly 25% of new COVID-19 cases are the Delta variant.

“What we’ve seen from the Delta variant is it tends to eventually out-compete, or become the dominant strain everywhere it’s had time to circulate,” said Dr. Ryan Westergaard, chief medical officer of the Wisconsin health department’s Bureau of Communicable Diseases.

But so far, western Wisconsin appears to be free of the Delta variant.

The state has tested 559 specimens from 15 of Wisconsin’s northwest counties, including Eau Claire County, and found no cases caused by the Delta variant. (Most of the state’s Delta cases are stemming from northeastern Wisconsin, according to state data.)

CDC Director Dr. Rochelle Walensky has said counties with vaccination rates below 30% are most vulnerable.

Eau Claire County clears that benchmark, with just over 50% of residents having received at least one dose of the vaccine. Regardless, vaccination rates in some surrounding counties are lower and Eau Claire health officials say they’re monitoring the Delta variant closely.

Audrey Boerner, public information officer for the Eau Claire City-County Health Department’s pandemic response, expressed concern that the variant could spur a surge of hospitalizations among unvaccinated people.

“For those who are not yet vaccinated, either because they are under age 12 or have chosen not to get the vaccine, we are concerned that we could see more cases because of how easily this variant spreads from person to person,” Boerner said in an email to the Leader-Telegram Thursday.

“Other parts of the country have seen increasing cases and hospitalizations as a result of the Delta variant and we are watching this closely.”

Several studies indicate that Delta — a strain of COVID-19 first documented in October in India — spreads much more quickly and easily than earlier strains, or as much as 50% more transmissible. It’s been found in more than 90 other countries since October.

It’s still unclear if the variant causes more severe illness or heightens the risk of death.

Studies have suggested some monoclonal COVID-19 antibody treatments might be less effective in infections caused by certain variants, according to the CDC.

Will Wisconsin ever see a surge of Delta variant cases?

“We’ve experienced this before with the Alpha variant,” Westergaard said, referring to a variant first documented in Britain. “Three to four months after it started peaking in Europe, we saw it become the predominant variant in the U.S. It’s possible, perhaps likely, that we’ll see that same pattern.”

Vaccines, Delta and efficacy

Researchers believe the Pfizer and Moderna shots do protect against the Delta variant — and are only slightly less effective.

“We have good evidence that the vaccines we have available in the U.S. provide protection against the Delta variant,” Boerner said.

In clinical trials last year, the Pfizer and Moderna vaccines originally reported about 95% effective in people who got both doses. Trials also indicated Johnson & Johnson’s vaccine is about 85% effective at preventing severe COVID-19 illness.

A new Moderna study concluded that the Moderna shots produce an antibody response that shields against Delta and other variants, though protection may be slightly lessened.

Oxford University researchers found a similar result for Pfizer and AstraZeneca vaccines: They’re also “broadly effective” against the Delta variant, though again, that protection might be very slightly reduced, Reuters reported.

About 67% of U.S. adults have gotten at least one dose, along with 61% of Eau Claire County residents.

Boerner said it’s crucial for people who got the Pfizer or Moderna vaccine to return for their second dose “to have the best protection against this or any other strain.”

To mask or not to mask?

The Delta variant so far hasn’t spurred the CDC to change its recommendations for masks.

Walensky on Wednesday reiterated the CDC’s stance that fully vaccinated people don’t have to wear masks in most situations, though unvaccinated people should still don them when in public.

The World Health Organization has taken a different tack. A WHO official last week urged fully vaccinated people to keep wearing masks indoors and socially distancing.

The Eau Claire City-County Health Department continues to follow CDC and state guidance, Boerner said, recommending that unvaccinated people wear masks in public but vaccinated people can leave them off in most circumstances.

Wisconsin health officials have continued to push vaccines in the wake of highly transmissible new variants.

“The stakes are higher, in a sense,” Westergaard said last week of the Delta variant. “It’s one reason that, right now in the summer, we want to encourage everyone to get vaccinated. Now is the time when we build up our protection … (it’s) one thing with more transmissible variants. We need a higher percentage of people vaccinated to prevent outbreaks.”

The Associated Press contributed to this report.

Contact: 715-833-9206, sarah.seifert@ecpc.com, @sarahaseifert on Twitter

Sarah Seifert is the L-T's education and health reporter. She has worked as a journalist in the Chippewa Valley since 2017 and joined the L-T in 2019. Get in touch at sarah.seifert@ecpc.com or on Twitter @sarahaseifert.