COVID-19 transmission in Washington is decreasing, though much of how the next few months unfold depends on upcoming holiday gatherings and seasonal behavior changes, according to the newest modeling report from the state Department of Health.

While cases, hospital admissions and deaths remain high in the state, trends are moving in the right direction, DOH’s most recent COVID-19 modeling and surveillance report says.

The report found that COVID-19 prevalence — the percent of residents with an active virus infection — has been declining significantly since early September. Last month, the state reported that virus prevalence was at a new high at 0.94%, or about 1 in every 106 people in the state. On Thursday, researchers reported prevalence around 0.41%, or 1 in every 244 Washingtonians.

The newest estimate reflects about a 50% drop in residents with an active COVID-19 infection since last month. Despite the decline, the report noted, “prevalence still remains high, similar to levels observed at the peak of the spring 2021 surge.”

Thursday’s report estimated a reproductive number — or Re, which shows how many additional people each positive person will infect — of roughly 0.83 as of early October, showing a drop from 1.14 last month, possibly brought on by increased preventive behaviors, like masking.

A reproductive number below 1 means cases could begin to decrease, though the number must stay below 1 for a “sustained period of time” to ensure a continuous drop in transmission.

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“We’re hopeful that the declines we’ve seen in the last few weeks will continue, but that will only be possible if vaccination rates continue to increase and we continue wearing masks,” Dr. Scott Lindquist, state epidemiologist for communicable diseases, said in a Thursday statement. “Our individual choices over the next several weeks will determine whether hospitals are able to return to a sustainable level of operations by the end of December.”

Researchers reported population immunity in Washington has rapidly increased since August and now sits at about 63.5% — about 20.3% of immunity was derived from previous infection, while 43.2% came from vaccinations. 

Long-term immunity, however, isn’t addressed in the data, so the estimates don’t account for waning of immunity.

Case counts have continued to decline in the past month. As of early October, the seven-day rolling average was 2,224 infections per day — down from the most recent peak of 3,552 on Sept. 13.

While the drop in cases has been recorded across all age groups, it began “noticeably later” for kids and teens younger than 19, the report said. Researchers noted the later decline could be related to the increased testing of kids as schools reopened this fall, since they didn’t observe the same pattern in hospitalizations.

Hospital admissions and deaths have also decreased recently, though hospitalizations remain high. The most recent count shows a seven-day rolling average of 115, or about 10.37 hospitalizations per 100,000 people. At this time last year, in comparison, the state counted 3.62 hospitalizations per 100,000. 

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The seven-day rolling average of deaths has slightly declined from 38 deaths per day in mid-September to 33 as of late September. The number is much higher than the state’s rolling average of deaths at this time last year, which epidemiologists recorded at about 8 before the winter surge.

Hospital admission rates — which remain at least nine times higher among the unvaccinated — remain fairly even in most age groups, though there’s some flattening in rates among those in their 30s and 50s. Occupancy, meanwhile, is still tight. The total number of hospital beds occupied by COVID-19 patients peaked in mid-September and beds have freed up since then, but occupancy remains around 90%.

Researchers are pointing to increases in staffing shortages and people seeking health care and elective procedures as reasons behind the continued high hospital occupancy. 

Future of hospital capacity

If transmission drops slightly over the next two weeks, projections show a slow increase in hospital occupancy through the end of December, with 400 to 790 beds occupied per day, the report said. However, in another scenario where the state sees a “moderate” increase in transmission, between 520 and 1,375 beds could be occupied per day by early November.

In either scenario, general hospital capacity would remain tight because of a backlog of delayed care and ongoing staffing shortages, as well as the potential spread of other respiratory viruses.

COVID-19 patients have taken up fewer beds since early September, and now make up about 17% of overall occupancy compared with nearly 25% a few weeks ago.

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“While vaccination provides much more protection this fall and winter compared to last year, exposure to COVID-19 and disease transmission continues to be influenced by our behavior,” the report said.

If Washingtonians, for example, relax preventive behavior and dive into travel and holiday gatherings, the state could find itself in a situation similar to last winter.

“Given the likelihood that high levels of occupancy will persist through the fall, any measures that can be taken to reduce transmission from now through the end of the year are warranted,” the report said.