Washington State Influenza Summary

2020-2021 Season

Washington State Department of Health, Communicable Disease Epidemiology

The Department of Health (DOH), in collaboration with local health jurisdictions and the Centers Disease

Control and Prevention (CDC), performed surveillance for influenza during the 2020-2021 season using

several different systems. This report summarizes data collected through key systems from September 27,

2020 to October 29, 2021 (week 40 of 2020 through week 39 of 2021).

Due to the COVID-19 pandemic, data reported from the various influenza surveillance systems may not represent an accurate

reflection of influenza activity. Results should be interpreted with caution, especially where comparisons are made to previous

influenza seasons.

National Summary

Influenza activity was unusually low throughout the 2020-2021 flu season both in the United States and

globally, despite high levels of testing. The low level of flu activity during this past season contributed to

dramatically fewer flu illnesses, hospitalizations, and deaths compared with previous flu seasons. COVID-19

mitigation measures such as wearing face masks, staying home, hand washing, school closures, reduced

travel, increased ventilation of indoor spaces, and physical distancing, likely contributed to the decline in 2020-

2021 flu incidence, hospitalizations and deaths. Influenza vaccination may also have contributed to reduced flu

illness during the 2020–2021 season. https://www.cdc.gov/flu/season/faq-flu-season-2020-2021.htm

Washington State Summary

In Washington State, zero laboratory-confirmed influenza deaths and zero influenza-like illness outbreaks in

long-term care facilities were reported for the 2020-2021 season. Unusually low influenza activity was likely a

result of influenza vaccination efforts and COVID-19 mitigation measures such as masking, staying home, and

limiting gatherings.

Influenza Laboratory Surveillance Data

Laboratory Data: World Health Organization (WHO) & National Respiratory and Enteric Virus

Surveillance System (NREVSS) Data Reported to CDC

For the 2020-2021 influenza season, CDC has generated separate graphs of data reported to CDC by public

health laboratories (Figure 1) and commercial laboratories (Figure 2).

Figure 1: Influenza Positive Tests Reported to CDC, WA Public Health Laboratories

Figure 2: Influenza Positive Tests Reported to CDC, WA Commercial Laboratories

Outpatient Influenza-like Illness Surveillance

Outpatient Influenza-like Illness Surveillance Network (ILINet) Data

Information on patient visits to health care providers for influenza-like illness is collected through the U.S.

Outpatient Influenza-like Illness Surveillance Network (ILINet). Each week, healthcare providers in Washington

reported data to CDC on the total number of patients seen and the number of those patients with influenza-like

illness (ILI) by age group. For the purposes of ILINet, ILI is defined as fever (temp 100

∘

F/37.8

∘

C or higher) plus

cough and/or sore throat. More information about ILINet is available here.

It should be noted that in addition to the overarching impacts of COVID-19 on influenza surveillance systems, interpretation of ILINet

influenza data during the 2020-2021 season should take into account the following COVID-19 impacts: changes in the health seeking

behavior at ILINet sentinel sites, changes to provider swabbing at ILINet sentinel sites due to the availability of telehealth and

respiratory clinics, and limited ability to distinguish between ILI and COVID-19 symptoms.

Figure 3: Percentage of ILI Visits Reported by Sentinel Providers, Washington, 2019-2021

Influenza-like Illness Syndromic Surveillance Data

ESSENCE Syndromic Surveillance Data

Figure 4 shows the proportion of visits at a subset of emergency departments across Washington for a chief

complaint of influenza-like illness, or discharge diagnosis of influenza, by CDC week. For this purpose, ILI is

defined as “influenza” or fever with cough or fever with sore throat.

It should be noted that in addition to the overarching impacts of COVID-19 on influenza surveillance systems, interpretation of

syndromic surveillance influenza data for the 2020-2021 season should take into account the following COVID-19 impacts: changes in

the health seeking behavior at syndromic surveillance sites and limited ability to distinguish between ILI and COVID-19 symptoms.

For more information about Syndromic Surveillance in Washington State, see:

www.doh.wa.gov/ForPublicHealthandHealthcareProviders/HealthcareProfessionsandFacilities/DataReportinga

ndRetrieval/ElectronicHealthRecordsMeaningfulUse/SyndromicSurveillance

Figure 4: Syndromic Surveillance, Percentage of Hospital Visits for a Chief Complaint of ILI, or

Discharge Diagnosis of Influenza, by CDC Week, Washington, 2017-2021

Influenza-like Illness Outbreaks in Long Term Care Facilities

Long term care facilities are required to report all suspected and confirmed outbreaks to their local health

jurisdiction per Washington Administrative Code (WAC) 246-101-305. Long-term care facilities are required to

report the following:

• A sudden increase in acute febrile respiratory illness over the normal background rate (e.g., 2 or more cases of

acute respiratory illness occurring within 72 hours of each other) OR

• Any resident who tests positive for influenza

This count of Influenza-like Illness Outbreaks does not include lab-confirmed COVID-19 outbreaks. For more

information on COVID-19 outbreaks, see the WA DOH Long-term care COVID-19 report:

https://www.doh.wa.gov/Portals/1/Documents/1600/coronavirus/data-tables/Weekly-COVID-19-Long-Term-

Care-Report.pdf

Recommendations for prevention and control of influenza outbreaks in long-term care facilities are available at:

http://www.doh.wa.gov/Portals/1/Documents/5100/fluoutbrk-LTCF.pdf

Local health jurisdictions in turn report long-term care facility influenza-like illness outbreaks to the Washington

State Department of Health.

Since Week 40 of 2020, 0 influenza-like illness outbreaks in long-term care facilities have been reported to the

Washington State Department of Health.

Other Causes of Respiratory Infections

During the 2020-2021 season, the following non-influenza respiratory viruses were reported to the National

Respiratory and Enteric Surveillance System (NREVSS). NREVSS does not capture COVID-19 testing data.

For more information on COVID-19, see https://www.doh.wa.gov/Emergencies/Coronavirus.

For more information about NREVSS, see https://www.cdc.gov/surveillance/nrevss/index.html.

Figure 5: Respiratory and Enteric Viruses, Washington, 2020-2021 Season

Laboratory Confirmed Influenza-Associated Deaths

Reported Laboratory-Confirmed Influenza Associated Deaths

Note that these counts reflect only deaths officially reported to the Washington State Department of Health and are likely under-

reported for a variety of reasons. Influenza may not be listed as a cause of death, influenza testing may not have been performed,

and lab-confirmed influenza deaths may not have been appropriately reported to public health. CDC has published information about

estimating seasonal influenza-associated deaths: www.cdc.gov/flu/about/burden/howcdcestimates.htm

Zero laboratory-confirmed influenza deaths have been reported during the 2020-2021 season: 0 influenza A, 0

influenza B, and 0 type unknown.

Table 1: Count and Rate of Reported Laboratory-Confirmed Influenza-Associated Deaths by Age

Group, Washington, 2020-2021

Age Group (in years)

Count of Deaths

Death Rate (per 100,000 population)

0-4

5-17

18-29

30-49

50-64

65+

Total

Reported Laboratory-Confirmed Influenza-Associated Deaths, Past Seasons

Lab-confirmed influenza death totals reported to the Department of Health for past seasons are presented

below in Table 2. Note that for the purposes of tables 2 and 3, each influenza season runs from week 40 of

one year to week 39 of the next (roughly October to October). Past season summaries are available on the

Department of Health website.

Table 2: Count of Reported Laboratory-Confirmed Influenza-Associated Deaths by Season

Season

Count of Deaths Reported for the Entire Season (week 40 to week 39)

2020-2021, to date

2019-2020

114

2018-2019

245

2017-2018

296

2016-2017

278

2015-2016

2014-2015

156

2013-2014

2012-2013

 
6 
 
Additional Resources 
 
International Influenza Data: http://www.who.int/topics/influenza/en/ 
National Influenza Surveillance Report: http://www.cdc.gov/flu/weekly/ 
 
Washington DOH Influenza Information for Public Health and Healthcare Providers: 
http://www.doh.wa.gov/ForPublicHealthandHealthcareProviders/PublicHealthSystemResourcesandServices/Im
munization/InfluenzaFluInformation#recommendation 
 
Washington Local Health Department Influenza Surveillance Reports: 
Clark County: https://www.clark.wa.gov/public-health/flu 
King County: http://www.kingcounty.gov/healthservices/health/communicable/diseases/Influenza.aspx 
Kitsap County: http://www.kitsappublichealth.org/Respiratory.pdf 
Pierce County: https://www.tpchd.org/healthy-people/provider-resources/disease-information-for-
providers/influenza/influenza-reports 
Whatcom County: http://www.co.whatcom.wa.us/967/Influenza 
Yakima County: http://www.yakimacounty.us/365/RSV-Flu-Stats 