Statewide COVID-19 cases are falling, but concern exists about potential fourth wave

By Dave Somers, Snohomish County Executive | Press Release

Snohomish County, Wash., March 16, 2021 – The state’s Department of Health late last week released the latest statewide situation report on COVID-19. A key concern: a possible fourth wave infection.

Progression of COVID-19 outbreak in WA state by cases per day, also know as the epidemiological curve. Source: DOH.

“When you look at our data, there is a pattern of several waves of COVID-19 activity followed by a return to baseline level. The baseline we reached after our second wave in summer 2020 was higher than the level after our first wave. Now, following the third wave that began last fall, cases have flattened out at higher baseline level than ever before,” said Acting State Health Officer Scott Lindquist, MD, MPH.

Statewide snapshot as of March 14, 2021. Source: DOH.

“I’m concerned about what this means for the future and a possibility of a fourth wave of activity, along with the increases we are seeing in variants of the virus. As we continue working to accelerate vaccination so we can protect more people, it’s critical that we all maintain the precautions we’ve been taking to stop the spread of the virus.”

Report findings include:

Case counts have increased slightly in western Washington and plateaued in eastern Washington as of late February. Case counts are still relatively high across the state—around the same level we were seeing last October when the third wave of disease activity was ramping up. Plateauing or increasing at these high levels is concerning.
Most counties have seen declines in case counts since the first week of January, but cases have flattened in several counties and are starting to increase again in others. Six of 39 counties had rates above 200 new cases per 100,000 people over the two-week period ending on Feb. 25. No counties had rates above 500 new cases per 100,000 people.
Cases are increasing among younger adults aged 20-29 and 30-39.This has previously been an early warning sign of larger surges in the general population. Case counts in other age groups were declining, but have now flattened. As more people who are 60 and older get vaccinated, we expect to see a more rapid decline in cases in this population.
We are seeing sharp declines in hospital admission rates among people 70 and older, possibly because those groups are among the first to get vaccinated. Admissions have declined at different rates depending on the age group. Overall, hospital admissions have flattened in eastern Washington and continue to decline in western Washington.
COVID-19 transmission is continuing at about the same level after declines through January and February. The best estimate of the reproductive number (how many new people each COVID-19 patient will infect) in the state on Feb. 19 was 0.96. The goal is to maintain a reproductive number well below one — meaning COVID-19 transmission is declining — for a substantial amount of time.
The estimated prevalence (percentage of people with active COVID-19 infections) began to plateau in early February after declines in January. High prevalence means there are a lot of people with infections who may need health care and could be spreading the virus to others. The best model-based prevalence estimate as of Feb. 19 was 0.11%.

Summary of key performance metrics – Snohomish County

Snohomish County COVID-19 case rates per 100,000. Data source: Snohomish Health District COVID-19 database.

COVID-related hospital admissions by week. Data source: Snohomish Health District COVID-19 database.

DOH partners with the Institute for Disease Modeling, Fred Hutchinson Cancer Research Center, University of Washington and the Microsoft AI for Health program to develop these reports every other week. More COVID-19 data can be found on the DOH data dashboard and in the state’s Roadmap to Recovery dashboard.