Infectious disease experts said the coronavirus may have infected millions unknowingly around the world, having preceded worldwide lockdown measures, in mid-March.

"Most people infected with coronavirus have an uncomplicated case of the virus, and it may not be distinguished from cold or influenza," said Amish Adalja, the first researcher at John Hopkins Center for Health Security in the United States, and an expert in infectious diseases.

Unfortunately, there is “no 100% sure-fire way to know” if the disease you dealt with last winter was COVID-19 or a common cold, according to doctors.

However, there are seven signs that could indicate a COVID-19 infection:

A cold in early 2020

Scientists analysed throat swabs taken last winter of suspected cases having influenza in the U.S. and China, and discovered that for every two cases of flu, there was one case of coronavirus.

Due to the similarity of symptoms, it may be difficult to distinguish between a cold and a mild case of COVID-19. However, colds do not usually cause shortness of breath or severe headaches.

Sense of smell and taste loss

A distinctive feature of coronavirus is the loss of smell and taste, while this symptom does not happen to everyone, Adalja said it is now strongly associated with COVID-19.

It is also possible to lose these two senses temporarily in the case of other respiratory diseases, such as colds, influenza, sinusitis, or seasonal allergies.

Hair loss

Many of those who recovered from coronavirus reported problems related to hair loss. Reasons could include a combination of factors, such as severe stress, or weight loss, said Adalja.

Shortness of breath

Scientific research published by GAMA Healthcare, found those infected with coronavirus may feel short of breath, possibly due to an infection in the lungs.

A persistent cough

One of the symptoms of coronavirus is a persistent and dry cough, which means no sputum or mucus appears, according to Adalja.

Collected data found 43% of people who contracted COVID-19 had a cough from 14 to 21 days after testing positive for the virus.

Feeling overwhelmed

The research published by GAMA Healthcare, found that 53% of COVID-19 cases experienced fatigue and exhaustion, about two months after symptoms first appeared.

It could be how the person's immune system interacts with the virus, or simply how the virus works in the body, said Adalja.

Symptoms that do not disappear

Coronavirus is new to doctors. Therefore, some of its symptoms and consequences remain hidden, such as those suffering from heart problems after infection.