Pandemic (H1N1) 2009 Virus


(Human Swine Influenza, Influenza A (H1N1))

Updated October 6, 2014

For general information on influenza and pandemic influenza, see our Influenza and Pandemic Influenza webpage

Pandemic (H1N1) 2009 Virus

Confirmed cases of Pandemic (H1N1) 2009 virus, commonly called 'swine flu', which originated in Mexico around March 18, 2009, have occurred around the globe and are now in decline. Many deaths have been associated with this outbreak.

In Canada, Pandemic (H1N1) 2009 virus was confirmed in all provinces and territories and carried a mortality rate of 1.3 per 100,000 population. The highest hospitalization rates occurred in children aged less than 5 years of age. Influenza activity for the 2009-2010 far exceed the expected range and occurred in two distinct waves. The peak period for the first wave was May 31/09 to June 20/09, and for the second wave October 25/09 to November 14/09). The 2013-2014 season saw another spike in cases across the country. For weekly reports, visit Canada's FluWatch site.

Pandemic (H1N1) 2009 virus totals in Canada:

Season # cases* # deaths
2008-2009 12262 77
2009-2010 33509 428
2010-2011 1024 n/a
2011-2012 1063 n/a
2012-2013 1274 1
2013-2014 10436 n/a

*(confirmed cases by subtyping)

The following information has been retained for historical purposes. Please note that some links may no longer be working.

Significant Events - 2009-2010

  • March 18/09: first cases in Mexico
  • April 25/09: WHO declares a Public Health Emergency of International Concern
  • April 26/09: the U.S. declares a public health emergency
  • April 27/09: WHO increases the pandemic alert level to phase 4, indicating sustained human-to-human transmission
  • April 28/09: PHAC issues a travel health warning, recommending that travellers from Canada postpone elective or non-essential travel to Mexico until further notice
  • April 29/09: WHO increases the pandemic alert level to phase 5, indicating widespread human infection and imminent pandemic
  • April 29/09: Canada provides laboratory testing support to Mexico
  • April 30/09: WHO refers to new influenza virus as Influenza A(H1N1)
  • May 6/09: Genetic makeup of H1N1 Flu virus decoded
  • May 18/09: PHAC lifts travel health warning to Mexico
  • June 11/09: WHO increases the pandemic alert level to phase 6, indicating that a global pandemic is underway
  • June 29/09: First case of oseltamivir-resistant H1N1 flu virus reported (Denmark)
  • July 1/09: WHO renames novel influenza virus as Pandemic (H1N1) 2009
  • July 3/09: First reported case of acquired oseltamivir-resistant H1N1 flu virus (Hong Kong)
  • July 13/09: WHO releases recommendations on pandemic (H1N1) 2009 vaccines
  • July 21/09: First Canadian case of aseltamivir-resistant H1N1 flu virus reported (Quebec)
  • September 16/09 : Canada announces H1N1 vaccine rollout sequencing
  • October 23/09: Canada officially enters second wave of Pandemic (H1N1) 2009
  • January 27/10: End of second wave of Pandemic (H1N1) 2009
  • August 10/10: WHO decreases pandemic alert level to the post-pandemic period, indicating worldwide flu activity has returned to typical seasonal patterns

Symptoms of Pandemic (H1N1) 2009 virus

Most cases of H1N1 flu have occurred in previously health young adults aged 25-44 years old or older adults with chronic underlying conditions such as diabetes, tuberculosis or cardiovascular diseases. Groups that appear to be at increased risk for severe disease and death from infection include persons with pulmonary disease such as asthma, immunosuppression, chronic heart disease, pregnant women, children under five years of age and those with chronic conditions. [ref: WHO].

Pregnant women are not more likely to get the H1N1 flu, but if they do get it, they are more likely to suffer complications such as pneumonia or severe respiratory distress. Severe complications from the flu could lead to early delivery or miscarriage. The H1N1 vaccine is recommended for all pregnant women at any stage of their pregnancy.

Clinical symptoms of H1N1 flu include: [ref: Public Health Agency of Canada]

Almost Always: Common: Sometimes:
Fever Sore throat Nausea
Cough Fatigue Diarrhea
  Muscle aches Vomiting
  Decreased appetite  
  Headache  
  Runny nose  

Rapid progression of symptoms to severe respiratory distress may occur within 5 days. Individuals should seek immediate medical attention if they have any of the following symptoms:

  • Shortness of breath, rapid or difficulty breathing
  • Chest pain
  • Bluish or grey skin colour
  • Bloody or coloured sputum
  • Severe or persistent vomiting
  • Sudden dizziness or confusion
  • High fever (>39.5° C) lasting longer than three days
  • Low blood pressure
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Prevention and Control Measures

Influenza is spread from person to person via droplets when coughing or sneezing and by touching objects and surfaces that are contaminated with the virus (e.g. doorknobs, telephones) and then touching their eyes, nose or mouth. The influenza virus may persist for hours in dried mucus and be transmitted by direct contact. It is spread very easily indoors, which is why it is so prevalent in the winter months in northern countries, when people spend more time together inside. A person with H1N1 flu is believed to be infectious one day before onset of symptoms and up to 7 days after the start of symptoms. [ref: Public Health Agency of Canada]

Measures to Reduce the Spread of Influenza

There is no evidence to suggest that wearing masks will prevent the spread of infection in the general population. Improper use of masks may in fact increase the risk of infection. Masks do not act as an effective barrier against disease when they are worn for extended periods of time. In addition, removing your mask incorrectly can spread virus to your hands and face.

Health Care Settings

In health care settings, Routine Practices should be used consistently with all patients including:

  • Hand hygiene before and after all patient contact (hand hygiene information is available on CHICA-Canada's Hand Hygiene website)
  • Appropriate use of personal protective equipment (gloves, masks, eye protection) for contact with all patient secretions/excretions
    • See SHEA's Position Statement: "Interim Guidance on Infection Control Precautions for Novel Swine-Origin Influenza A H1N1 in Healthcare Facilities"
  • Disinfection of all equipment which is shared between patients with a disinfectant registered for use against Influenza A viruses (more information)
  • Cleaning/disinfection of all patient contact surfaces after patient leaves an examining room or area with a disinfectant registered for use against Influenza A viruses (more information)

Emergency Departments should apply screening to all patients who present with respiratory symptoms. Laboratory testing for Pandemic H1N1 2009 virus is not recommended for patients with mild illness. Specimens should only be submitted for testing where lab results are required for clinical management of hospitalized cases of influenza-like illness (ILI) or where patients are at high risk for complications from influenza.

There is no risk of infection from this virus from consumption of well-cooked port or pork products.

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Treatment of Influenza [Ref: World Health Organization]

Treatment of influenza usually involves making the person more comfortable – increasing fluid intake and getting plenty of rest. Antibiotics do not kill viruses and have no role in treating influenza in otherwise healthy people, although they may be used to treat complications, such as pneumonia.

Antiviral drugs for influenza are an important adjunct to influenza vaccine for the treatment and prevention of influenza. However, they are not a substitute for vaccination. When taken before infection or during early stage of the disease (within two days of illness onset), antivirals may help prevent infection, and if infection has already taken hold, their early administration may reduce the duration of symptoms by one to two days.

Laboratory testing has found the Pandemic (H1N1) 2009 virus to be resistant to amantadine and rimantidine and susceptible to the prescription antiviral drugs oseltamivir and zanamivir, although isolated cases of resistance have occurred.

In severe influenza, admission to hospital, intensive care, antibiotic therapy to prevent secondary infection and breathing support may be required.

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Travel Advisories - PHAC

Updated May 18, 2009

As of May 18, 2009, the Public Health Agency of Canada no longer recommends Canadians postpone elective or non-essential travel to Mexico.

PHAC recommends that travellers at risk of complications from any form of influenza such as those with chronic conditions (for example diabetes, lung disease, heart disease), elderly, pregnant women or children under 2 years of age, discuss the risk of travel with their health care provider before going to Mexico.

More information

Pandemic (H1N1) 2009 Virus Links

CHICA-Canada
Public Health Agency of Canada (PHAC)
World Health Organization (WHO)
U.S. Organizations
Provincial Information
British Columbia Alberta Saskatchewan Manitoba Ontario Quebec New Brunswick Nova Scotia Prince Edward Island Newfoundland Northwest Territories Nunavut Yukon
Pandemic Influenza

Pandemic (H1N1) 2009 virus PUBLICATIONS

See also: The Lancet's H1N1 Flu Resource Centre

  • MMWR April 24, 2009: Swine Influenza A (H1N1) Infection in Two Children - Southern California, March-April 2009
  • MMWR May 1, 2009: Update: Swine Influenza A (H1N1) Infections - California and Texas, April 2009
  • MMWR May 1, 2009: Update: Drug Susceptibility of Swine-Origin Influenza A (H1N1) Viruses, April 2009
  • MMWR May 1, 2009: Update: Infections With a Swine-Origin Influenza A (H1N1) Virus - United States and Other Countries, April 28, 2009
  • MMWR May 1, 2009: Update: Swine-Origin Influenza A (H1N1) Virus - United States and Other Countries
  • MMWR May 8, 2009: Swine-Origin Influenza A (H1N1) Virus Infections in a School --- New York City, April 2009
  • MMWR May 8, 2009: Outbreak of Swine-Origin Influenza A (H1N1) Virus Infection --- Mexico, March--April 2009
  • MMWR May 8, 2009: Update: Novel Influenza A (H1N1) Virus Infections --- Worldwide, May 6, 2009
  • Science May 11, 2009: Pandemic Potential of a Strain of Influenza A (H1N1): Early Findings
  • Eurosurveillance May 14, 2009: A Preliminary Estimation of the Reproduction Ratio for New Influenza A (H1N1) From the Outbreak in Mexico, March-April 2009
  • MMWR May 15, 2009: Novel Influenza A (H1N1) Virus Infections in Three Pregnant Women --- United States, April--May 2009
  • Biochemical and Biophysical Research Communications May 20, 2009: Susceptibility of antiviral drugs against 2009 influenza A (H1N1) virus
  • MMWR May 22, 2009: Hospitalized Patients with Novel Influenza A (H1N1) Virus Infection - California, April - May, 2009
  • MMWR May 22, 2009: Serum Cross-Reactive Antibody Response to a Novel Influenza A (H1N1) Virus After Vaccination with Seasonal Influenza Vaccine
  • Eurosurveillance May 28, 2009: Cluster analysis of the origins of the new influenza A(H1N1) virus
  • Eurosurveillance June 4, 2009: Origins of the new influenza A(H1N1) virus: time to take action
  • Eurosurveillance June 4, 2009: Evaluation of four real-time PCR assays for detection of influenza A(H1N1)v viruses
  • Journal of Clinical Virology June 5, 2009: Emergence of a novel swine-origin influenza A virus (S-OIV) H1N1 virus in humans
  • MMWR June 5, 2009: Update: Novel Influenza A (H1N1) Virus Infection --- Mexico, March-May, 2009
  • SHEA June 10, 2009: Position Statement: Interim Guidance on Infection Control Precautions for Novel Swine-Origin Influenza A H1N1 in Healthcare Facilities
  • MMWR June 19, 2009: Novel Influenza A (H1N1) Virus Infections Among Health-Care Personnel --- United States, April--May 2009
  • ScienceInsider July 3, 2009: Oseltamivir-resistant H1N1 Flu Virus indicates acquired resistance
  • MMWR July 30, 2009: Prevention and Control of Seasonal Influenza with Vaccines. Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009
  • MMWR August 6, 2009: Evaluation of Rapid Influenza Diagnostic Tests for Detection of Novel Influenza A (H1N1) Virus - United States, 2009
  • MMWR August 27, 2009: Use of Influenza A (H1N1) 2009 Monovalent Vaccine: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009
  • MMWR September 25, 2009: Performance of Rapid Influenza Diagnostic Tests During Two School Outbreaks of 2009 Pandemic Influenza A (H1N1) Virus infection - Connecticut, 2009
  • MMWR October 8, 2009: Update on Influenza A (H1N1) 2009 Monovalent Vaccines
  • MMWR November 12, 2009: Effectiveness of 2008-09 Trivalent Influenza Vaccine Against 2009 Pandemic Influenza A (H1N1) - United States, May-June 2009
  • Eurosurveillance November 12, 2009: A Simple Mathematical Approach to Deciding the Dosage of Vaccine Against Pandemic H1N1 Influenza
  • Eurosurveillance November 19, 2009: Differentiation of two distinct clusters among currently circulating influenza A (H1N1)v viruses, March-September 2009
  • Eurosurveillance December 10, 2009: Prolonged Shedding of Influenza A (H1N1)v Virus: Two Case Reports from France 2009
  • MMWR December 10, 2009: Safety of Influenza A (H1N1) 2009 Monovalent Vaccines - United States, October 1-November 24, 2009
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