Increasing Influenza A (H3N2) Activity in the Public Health Sudbury & Districts area

Advisory Alert

April 23, 2019

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To: Community Health Care Providers

Re:  Increasing Influenza A(H3N2) Activity in the Public Health Sudbury & Districts area

This is an update on the current influenza season. Increased vigilance is warranted for influenza A infection in your patients presenting with signs and symptoms of respiratory infection.

Please note that we are currently seeing an increase in H3 activity within the Public Health Sudbury & Districts catchment area. This is a trend that is being observed elsewhere.

As of April 6, 2019, 11,159 laboratory-confirmed influenza cases have been reported in Ontario. Among these cases, 97.9% (10,922/11,159) were influenza A, and of those with subtype information available (2,450), 40.7% were H3N2 and 59.3% were H1N11. An increase in the proportion of laboratory-confirmed influenza cases reported as H3 has been observed compared to earlier in the season, where predominantly H1 was reported1. There is currently very little influenza B circulation compared to previous seasons1. Across Canada, 57% of all influenza A (H3N2) detections have been reported in adults 65 years of age and older2.

Estimates from the Canadian Sentinel Practitioner Surveillance Network suggest the 2018/19 influenza vaccine provides substantial protection against 2018/19 A(H1N1)pdm09 but little or no protection against influenza A(H3N2) viruses this season.

Please consider the timely administration of antivirals (e.g. oseltamivir or zanamivir), where indicated, in accordance with current guidelines from the Association of Medical Microbiology and Infectious Disease Canada (PDF, 182 KB).

Laboratory confirmation of influenza is not required prior to administration1.

Although treatment is generally more beneficial if given early, it can still be considered in those at high risk for influenza complications, even if more than 48 hours has passed from symptom onset. Use of influenza antiviral medication is also recommended, regardless of time from symptom onset, for:

For more information please refer to the fact sheet on antiviral medication (Public Health Ontario).

Should you have any questions, please contact our immunization program at 705.522.9200, ext. 301.


Penny Sutcliffe, MD, MHSc, FRCPC
Medical Officer of Health and Chief Executive Officer

  1. Ontario Agency for Health Protection and Promotion (Public Health Ontario). Ontario Respiratory Pathogen Bulletin – Week 14, 2019. Accessed at:
  2. Public Health Agency of Canada. FluWatch report: March 31 to April 6, 2019 (Week 14). Accessed at:
  3. Ontario Agency for Health Protection and Promotion (Public Health Ontario). Antiviral medications for influenza: information for health care providers. Toronto, ON: Queen’s Printer for Ontario; 2017.

This item was last modified on April 24, 2019