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Common cold and flu season is here!

Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer

As the cold weather arrives, so too does the season of common cold and flu. It’s the same every year. Why are respiratory viral infections more common when it gets cold? One reason is that the flu virus is very sensitive to humidity and hot weather. Dry environments and cold temperatures, both indoors and out, are therefore a welcoming environment. Also, people stay indoors longer, and are therefore in closer contact with each other. Shorter days might also be a factor — vitamin D and melatonin both require sunlight for their production. Low levels of vitamin D and melatonin have been associated with a reduced activity of the immune system [1].

Read more : The difference between the flu and a cold

How can we protect ourselves from the cold?

Apart from living in total isolation, there is no surefire way to protect yourself against the common cold. No vaccine or treatment is available for the more than 200 different viruses responsible for the common cold.

Multiple recommendations can be found on the web, and many are just good common sense: wash your hands frequently, avoid touching your face, keep household surfaces and objects clean, use disposable items and paper towels if a family member is infected.

Other suggestions may be some help even though most of them are not supported by strong scientific evidence. For example, taking supplements of Vitamin C, D, E or Zinc or echinacea, ginseng or probiotics. Good sleep hygiene is also associated with a more efficient immune system.

Coughing in your elbow or wearing a surgical mask is probably better at protecting others than it is yourself. Be considerate where you can.

Read more: Does eating oranges help cure a cold ?

What about the flu?

You can be immunized against flu (influenza), though the effectiveness of flu vaccines varies from year to year with an average efficacy of 60%, and with wide variation. A record low of 19% efficacy was observed in 2014–15 [2].

This variation is a result of the laborious and time-consuming process of vaccine preparation. The mixture of viral strains that can cause the flu varies each year, and in order to have enough doses of vaccine in time for fall immunization campaigns, the formulation must be based on the flu strains that have circulated elsewhere in previous months. (For us in Canada, this means flu strains that have recently caused epidemics in the southern hemisphere.) However, there is no guarantee that all of these strains, or only these strains, will be present here in the coming season, and unexpected flu strains regularly appear.

That being said, 60% or even 20% protection against an infection that can be lethal in a significant percentage of the population is better than no protection at all. Selected groups of individuals at higher risk of complications from the flu (young children, older people, pregnant women, and people with certain chronic health condition) are the ones that will benefit the most from annual flu immunization. In many parts of the world, including Quebec, state health authorities will organize flu vaccine programs free of charge to people in these higher risk populations [3].

Strep A sore throat

Sore throat (pharyngitis) is almost always caused by a virus. Bacterial infection of the throat by group A streptococcus, however, is responsible for 20% to 30% of pharyngitis (the medical term for a sore throat) in children and 5% to 15% in adults.

Strep A infection is not as closely associated as the flu virus with the cold season. Strep A infection can occur any time, but is more prevalent in winter and early spring and fall as the bacteria flourish when groups of people are in close contact.

Signs and symptoms

Signs and symptoms of sore throat include:

  • fever;
  • a throat pain that usually comes on quickly;
  • painful swallowing;
  • red and swollen tonsils sometimes with white patches of pus;
  • tiny red spots on the palate;
  • swollen tender lymph nodes in the neck.


Unlike a viral infection, which will resolve by itself, a bacterial sore throat requires antibiotic treatment. An untreated strep A infection can lead to scarlet fever (an inflammatory disease that affects several organs) or complications such as rheumatic fever or post-streptococcal kidney disease (glomerulonephritis).

Read more: Biron improves diagnostic procedure for strep throat with new molecular test

To prevent the development of antibiotic resistant strains of bacteria, it is not recommended that all cases of sore throat be treated with an antibiotic, but only those that are strep A positive. As signs and symptoms of a strep A sore throat can also be due to a viral infection, a strep A infection is usually confirmed by identifying the presence of bacteria with a throat swab (rapid strep test). A positive rapid strep test is highly suggestive of a strep A infection and an antibiotic treatment can be instituted without delay.

The situation is a little more complex when the rapid strep test is negative. Non-positive direct strep tests need to be confirmed in the lab. Traditionally, strep A confirmation is done by performing a throat culture, which may take as long as 48 hours after sampling to provide definitive results. Two days are therefore required before beginning symptom suppressive treatment. Due to advances in molecular testing, some tests are now available that can be done in a few minutes, allowing the patient and their physician to view their results on the same day as the throat sampling. This test is based on identifying the specific Strep A DNA signature and is as reliable as the result of a 48 hour culture.

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  1. Elert, Emily. “FYI: Why Is There A Winter Flu Season?” Popular Science, July 2, 2019.
  2. “CDC Seasonal Flu Vaccine Effectiveness Studies.” Centers for Disease Control and Prevention. Consulted on October 1, 2019.
  3. “Flu Vaccination Program.” Gouvernement du Québec. Consulted on November 7, 2019.
Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer