COVID-19: what it is, signs, and types of the virus

COVID-19 is an infectious disease caused by the coronavirus SARS-CoV-2. In most infected people it is mild or asymptomatic, but some cases result in severe lung damage. Below is a brief overview of the pathogen, virus variants, signs, and when medical help is needed.

COVID-19: what kind of disease it is

COVID-19 is a potentially severe acute respiratory infection. The causative agent is the betacoronavirus SARS-CoV-2, which had not previously been found in humans: on December 31, 2019, WHO received a report of pneumonia of unknown origin, and on March 11, 2020, the epidemic was declared a pandemic.

A Chinese report on 72,314 cases: 81% mild, 14% severe, 5% critical. Other estimates are similar: about 80% of those affected do not need specific treatment and recover on their own, 15% require oxygen therapy, and 5% are in critical condition.

People of all ages are affected; the median age of infected individuals is 50 years. Severe course is more common in people over 60 and in those with comorbidities. Complications include viral pneumonia with the risk of acute respiratory distress syndrome and respiratory failure, multiple organ failure, septic shock, and venous thromboembolism. Long-term consequences are also possible — post-COVID syndrome; in children and adolescents, an inflammatory syndrome is suspected in rare cases.

The risk of severe disease is increased by:

• age over 60 years;
• asthma;
• diabetes;
• heart disease.

The COVID-19 virus: how it is structured and transmitted

SARS-CoV-2 belongs to the subgenus Sarbecovirus. Transmission is airborne: when coughing, sneezing, or talking, a person exhales droplets and very fine particles containing the virus. The second route is that the virus settles on surfaces and from there enters the eyes, nose, or mouth.

The pathogen affects various organs — directly or through the body's immune response. Therefore, in severe cases, not only the lungs but also the heart, kidneys, and liver are affected.

Masks reduce transmission, but they work together with distancing, avoiding prolonged stays in enclosed spaces with large numbers of people, frequent handwashing, and respiratory hygiene. Vaccination reduces the risk of death, severe course, symptomatic cases, and infection itself; after it, short-term mild side effects are possible — headache, muscle pain, chills, and fever.

Seasonality has not been confirmed: as of 2025, no pronounced seasonality has been identified, and no association between the rate of spread and air temperature in Chinese cities has been found.

Types (variants) of COVID

Early data show that the Omicron strain causes a less severe infection than previous variants.

Signs of COVID

The most common symptoms are fever, dry cough, fatigue, and loss of taste or smell. Less often there is body aches, sore throat, diarrhea, conjunctivitis, headache, skin rash, and discoloration of the fingers or toes.

Loss of smell is highly specific and may occur without fever and cough. The median duration of loss of smell or taste is about 8 days.

Signs of new COVID: how it differs

The symptoms of COVID remain the same: fever, cough, fatigue, and loss of taste or smell.

Diagnosis and when to see a doctor

Diagnosis includes testing for SARS-CoV-2, including rapid tests.

In people over 60 and in those with asthma, diabetes, or heart disease, severe course is more likely to develop, so the condition is assessed by a doctor.

Having COVID alone is not a reason to call an ambulance. 103 or 112 — if shortness of breath or difficulty breathing, chest pain or a feeling of chest tightness, or loss of the ability to move or speak occurs.

This material is for reference: it describes the general signs of COVID and does not replace consultation with a doctor, who assesses the condition individually.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer