2020-2021 Influenza Season Surveillance, Testing and Treatment

Published Oct. 2, 2020.


Seasonal influenza surveillance begins in October and continues through April. We expect influenza and SARS-COV-2 to circulate simultaneously. To aid testing and treatment decisions this season, it is critical providers stay up to date on local influenza and COVID-19 activity.


CDC recommends influenza vaccine for everyone over age 6 months without contraindications to the vaccine. It is best to vaccinate people as soon as vaccine is available and before influenza begins circulating in the community. Continue to give influenza vaccine throughout the season, into spring. Never miss an opportunity to vaccinate.

Different vaccine products are available, with different age indications. Make sure staff use the right product for each patient.


Our influenza surveillance relies on reporting from healthcare facilities and providers. Call us at (360) 414-5599 to report:

  • Lab-confirmed influenza death—within 3 days.
  • Patient with suspected novel influenza virus—immediately.
  • Outbreak of influenza-like illness or lab-confirmed influenza in congregate care (e.g., long-term care facility)—immediately.


Use molecular testing (e.g., PCR for influenza) for all hospitalized patients with influenza-like illness. Be aware rapid enzyme immunosorbant assay (EIA) has a low sensitivity (between 50% and 70%, depending on the product). Interpret results based on the patient’s symptoms and influenza activity in the community. Positive and negative predictive values vary considerably depending on the prevalence of influenza in the community.

  • False-positive (and true-negative) results are more likely when prevalence is low, generally at the beginning and end of the season.
  • False-negative (and true-positive) results are more likely when prevalence is high, typically at the height of the season.

When influenza is actively circulating, treat with antiviral medications patients at high risk for complications who present with influenza-like symptoms, regardless of rapid test results. People at high risk for complications:

  • Children under age 5 (especially under age 2).
  • Adults age 65 or older.
  • Pregnant women.
  • People with diabetes, asthma, heart disease, morbid obesity or other chronic health conditions.


Early antiviral treatment can shorten the duration of fever and illness symptoms and may reduce the risk of complications (e.g., otitis media in young children, pneumonia, respiratory failure). Early treatment of hospitalized patients may reduce the risk of death. Early antiviral treatment of hospitalized children has been shown to shorten the duration of hospitalization. Antiviral medications work best when given within 48 hours of symptom onset. See CDC’s antiviral medications summary for clinicians for more information.


CDC recommends chemoprophylaxis for institutional influenza outbreaks. Providers may want to prescribe chemoprophylaxis for at-risk household members of patients with influenza. See the Infectious Diseases Society of America’s clinical practice guidelines for more information.

Influenza and SARS-CoV-2 co-circulation

Influenza and COVID-19 frequently have similar symptoms. Testing can help distinguish between the viruses. However, a positive test for one virus does not necessarily rule out infection with the other. Co-infection with both viruses can occur and should be considered, particularly in hospitalized patients with severe respiratory disease. It is critical providers stay up to date on local influenza and COVID-19 activity.

When both viruses are circulating in the community, empiric antiviral treatment of influenza is recommended as soon as possible for the following priority groups:

  • Hospitalized patients with respiratory illness.
  • Outpatients with severe, complicated, or progressive respiratory illness.
  • Outpatients at higher risk for influenza complications who present with any acute respiratory illness symptoms (with or without fever).

When a patient presents with influenza-like illness, test for both influenza and SARS-CoV-2. Healthcare providers can manage patients not severely ill and not at high risk for complications via telemedicine and refer to a community site for COVID-19 testing. Testing for COVID-19 is important to identify cases so they can isolate, and their contacts can quarantine.

  • People with confirmed COVID-19 (lab-confirmed or have symptoms plus close contact with a lab-confirmed case) should isolate for 10 days after symptom onset and until fever-free for 24 hours.
  • People with influenza should stay home for 4-5 days after symptom onset or until fever-free for 24 hours.