Omicron’s BA.5 subvariant continued to tear through Washington state in June, more than tripling its share of the state’s sequenced COVID-19 cases and contributing to high levels of infection in King County.

As of the week ending June 25, BA.5 constituted 37.3% of sequenced COVID cases, up from 9.8% during the week of May 29, according to the most recently available data released Wednesday.

What the BA.5 subvariant could mean for the U.S.

The BA.5 variant is now the dominant version of SARS-CoV-2 in the country, according to the Centers for Disease Control and Prevention. And while it’s hard to get an exact count — given the popularity of at-home testing — there are indications that reinfections and hospitalizations are increasing.

In King County, rates of COVID community transmission remain high — higher than they were during the peak of last summer’s delta surge, but still far from January’s omicron-wave levels, county health officer Dr. Jeff Duchin said in a Thursday news briefing.

As of Thursday, the county counted an average of about 941 daily cases, compared to about 620 daily cases in mid-August last year.


While COVID deaths remain relatively low, virus hospitalizations in King County have tripled since April, though they’re not rising as quickly as they did during past waves, Duchin said.

More on the COVID-19 pandemic

“The COVID-19 pandemic with the rapid evolution of new variants is challenging us in new ways we did not anticipate, and it requires long-term sustained prevention strategies,” he said. “It’s critical to understand that complacency is not the cure.”

Although there is a significant undercount of the true infection rate, the share of positive tests is surging and is now higher than during most other waves of the pandemic. BA.5 and BA.4 are the most transmissible versions of the coronavirus yet, evading immunity from previous infections and vaccines.

COVID cases in Washington are on the rise but it’s difficult for health authorities to put a finger on accurate rates of transmission.

“Cases overall seem to be slightly rising at this stage, though it is difficult to determine if these short-term trends are more representative of testing rates versus actual infections,” Rachael Sims, spokesperson for the Washington State Department of Health, said in a statement.


Besides at-home tests not being reported to health authorities, Sims added that some residents may not even get tested for various reasons.

In King County, there are no definite plans to return to indoor mask mandates, but the county is “actively considering” if and when additional public health requirements might be necessary, Duchin said.

“It’s not an easy question because things change over time,” he said. “For example, if we were seeing the level of severity before people were as well-vaccinated as they are now, or during the delta surge, I think we would be moving more quickly to such measures.”

Instead, public health leaders are first hoping community members will voluntarily renew their commitment to indoor masking, distancing, good indoor air ventilation and getting vaccinated and boosted.

“COVID-19 is not one and done,” Duchin said. “We’re not going to be able to have infinite series of mandates.”

Restrictions have a role if there is a serious need for short-term and immediate improvement, he said, adding that for the long term, the public needs to take steps to protect themselves and others.


He attributed much of the current surge to the “unexpected rapid evolution of highly infectious COVID variants, one after the next.”

As of a few weeks ago, the CDC estimated that the BA.5 subvariant, and to a lesser degree BA.4 — both of which became dominant omicron subvariants in South Africa in April — are causing between 65% and 90% of infections in Alaska, Idaho, Oregon and Washington, Duchin noted.

According to DOH data, the BA.2.12.1 omicron subvariant made up close to half of all state sequenced COVID-19 cases in June, while BA.2 declined from 37% at the start of the month to 11.7% three weeks later.

The sequencing data comes from 6.2% of all reported COVID-19 cases in the state, which DOH randomly selected for sequencing. Its Wednesday report includes data from over 60 labs across the state, which either contributed testing specimens or sequencing data.