COVID_19, FLU OR COLD: What are the differences?


It can be difficult to separate a flu, Covid-19, or a rhinovirus infection (which causes what is commonly known as the common cold) based on a simple clinical diagnosis.

“With practice and experience, we manage to distinguish them, and it is above all according to the epidemic context, the contacts that a patient may have had at school, or at work, etc. that we ‘directs towards a diagnosis (which must be confirmed by virological test for Covid-19)”, explains Dr Jean-Louis Bensoussan.

Each of these diseases is linked to a specific virus

  • The flu is linked to the influenza virus type A or B (Orthomyxoviridae family).
  • Covid-19 is linked to the new coronavirus SARS-CoV-2 (family of Coronaviruses (Coronaviridae).
  • The common cold (nasopharyngitis) is generally linked to a rhinovirus (Picornavirus family), of which there are hundreds of variants, and which remains confined to the nose and throat. “They circulate more or less all year round, especially in September / October, before epidemics of influenza and respiratory syncytial virus (RSV),” explains Sylvie Behillil.

The intensity of the symptoms, a factor to take into account

Rhinoviruses circulate throughout the year, which is why you can sometimes catch a cold in the middle of summer. Most of the time, they cause a simple cold, which sets in slowly and can result in congestion and runny nose, sneezing, headache, sore throat, and mild fatigue for three to five days. “However, it happens that patients present a high fever which suggests a flu-like syndrome, or even an onset of Covid-19, indicates Dr. Bensoussan. Likewise, some people go through influenza or Covid-19 with few, if any, symptoms, specifies Dr. Bensoussan ”.

The main factor that clinically differentiates a cold from the flu and Covid-19 is the intensity of the symptoms. Most patients with rhinovirus infection are able to work, go about their daily tasks. This is less often the case when a patient suffers from the flu or Covid-19.

Flu or Covid-19: can we distinguish them clinically?

Influenza, caused by influenza viruses type A (virus A (H1N1) pdm09 or A (H3N2)) and type B (B Yamagata and B Victoria), usually manifests with high fever, chills, headache, muscle pain (stiffness), and a dry cough. Some patients may have a runny or blocked nose or even a sore throat. “All these symptoms appear suddenly and persist for three to seven days, most frequently in winter and early spring, during an epidemic period. If the patient has been vaccinated against the flu, he can still develop much milder signs, depending on the virus to which he has been exposed, ”says Sylvie Behillil.

Covid-19 can cause the same symptoms (which appear gradually – not suddenly – and less specific): fever, persistent cough, loss of taste, loss of smell, fatigue, muscle stiffness, headache, sore throat, shortness of breath. More rarely, patients may experience nasal congestion or runny, diarrhea, and even neurological or skin symptoms. “Due to the many asymptomatic cases (40% of infected subjects, according to a study published in December 2021? Source 1), it is also more difficult to detect”, notes Dr. Bensoussan.

Anosmia (loss of smell) and ageusia (loss of taste) can occur in COVID patients as well as in patients with severe colds or patients with the flu.