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What is Influenza (“the flu”)?

Seasonal influenza, also known as “the flu,” is a common, highly contagious respiratory infection that’s caused primarily by Influenza A and Influenza B viruses. The flu typically circulates in Ontario in the fall and winter.


Signs and Symptoms of Influenza

Flu symptoms usually appear one to four days after a person has acquired the virus and can be similar to symptoms of COVID-19. Common symptoms of influenza can include;

  • Fever
  • Cough
  • muscle aches and pain
  • headache
  • chills
  • fatigue (tiredness)
  • loss of appetite
  • sore throat
  • runny or stuffy nose

While anyone can get the flu, individuals in the following groups are considered to be at high risk of severe complications:

  • Children six to 59 months (five years) of age;
  • Adults 65 years of age and older;
  • All pregnant individuals;
  • Residents of long-term care and chronic care facilities;
  • Indigenous peoples; and
  • Adults and children with the following chronic health conditions:
  • cardiac or pulmonary disorders (including bronchopulmonary dysplasia, cystic fibrosis, and asthma);
  • diabetes mellitus and other metabolic diseases;
  • cancer, immune compromising conditions (due to underlying disease, therapy, or both, such as solid organ transplant or hematopoietic stem cell transplant recipients);
  • renal disease;
  • anemia or hemoglobinopathy;
  • neurologic or neurodevelopment conditions (includes neuromuscular, neurovascular, neurodegenerative, neurodevelopmental conditions, and seizure disorders [and, for children, includes febrile seizures and isolated developmental delay], but excludes migraines and psychiatric conditions without neurological conditions);
  • morbid obesity (BMI of 40 and over); and
  • children six months to 18 years of age undergoing treatment for long periods with acetylsalicylic acid, because of the potential increase of Reye’s syndrome associated with influenza.


How is Influenza Spread?

Individuals with the flu can spread the virus when they cough, sneeze or talk. Droplets from an infected person can land in the mouth or nose of others who are nearby or can be inhaled into a person’s lungs. People can also get the flu by touching a surface that has the flu virus on it or by shaking hands with someone who has the flu and then touching their own eyes, mouth, or nose.


How is Influenza treated?

Similar to COVID-19, antiviral drugs are available for those at increased risk of serious complications from influenza infection. Speak with your healthcare provider if you think you would benefit from antiviral treatment. 


Influenza Vaccination

The influenza vaccine is the most effective way to prevent influenza illness and influenza-related complications. Flu vaccines are free, and safe – including for kids and pregnant individuals – well-tolerated and are available via primary care providers, participating pharmacies, and Grey Bruce Health Unit clinics.

Individuals six months of age and older who do not have contraindications to the vaccine should get the influenza vaccine each year. Vaccination is required each year because the contents of flu vaccines can vary from year to year. The World Health Organization reviews the specific strains in flu vaccines annually and can change them to provide a better match against the strains that the organization expects to see circulating in that given year. In addition, a person’s immune response to the flu vaccine may not continue beyond a year.

While the National Advisory Committee on Immunization strongly recommends that individuals get vaccinated before the onset of the flu season, the influenza vaccine can be administered until the end of the season.

The bottom line is, the sooner someone can get vaccinated within the flu season, the better.


COVID-19 Information

RSV Information


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