Early antiviral treatment is recommended for patients at high risk of complications presenting with influenza-like illness.

Key messages

• We are currently experiencing a late-season increase in influenza A (H3N2)
• Vaccine effectiveness against influenza A (H3N2) viruses is lower compared to influenza A (H1N1) or influenza B viruses
• Early initiation of antiviral medications is recommended for patients with suspected influenza at high risk of complications

Recent influenza activity

 A late-season surge in influenza A (H3N2) began in the last week of February (Figure 1). We anticipate that it will continue for several more weeks. For further information, see the BC Influenza Surveillance Bulletin.

Influenza A (H3N2)

H3N2-predominant seasons are typically associated with more hospitalizations and deaths in people aged 65 years and older. Influenza vaccine effectiveness against influenza A (H3N2) viruses is generally lower compared to influenza A (H1N1) or influenza B viruses.

Antiviral treatment

Given the late-season increase in H3N2 this season, please:

1. Keep influenza on the differential, and consider antiviral treatment for high-risk patients with suspected influenza including patients with chronic medical conditions, those aged 65 years or older, Aboriginal Peoples, and pregnant women or women up to 4 weeks post-partum. 
2. Antiviral medications are most effective when started within 48 hours of symptom onset. It is not necessary to wait for laboratory confirmation. 
3. Circulating influenza strains are susceptible to both oseltamivir and zanamivir. 

Antiviral treatment is not routinely recommended for adults at low risk of complications. Children under 5 are at increased risk for complications, however, antiviral therapy is not routinely required for children with mild or uncomplicated illness and no other risk factors for severe disease. For more information, see the antiviral use guidelines from AMMI Canada.