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SARS-CoV-2 coronavirus and COVID-19: Key information

Who is most at risk of infection and falling ill? What preventive action can we take? What is the mortality rate? We have prepared answers to some of the most frequently asked questions.

Wizualizacja koronawirusa widzianego pod mikroskopem

Coronavirus

Coronaviruses are RNA viruses in the family Coronaviridae, first described in the 1960s. Their name is derived from the Latin corona meaning “crown”, referring to the distinctive pattern of protein structures forming a halo around the virus particle. The viruses are spherical with a diameter of approx. 120 nm. They have a single-strand RNA genome ranging between 27 and 34 kilobases – one of the largest in their class.

Scientists have described several coronaviruses causing infections in different mammal and bird species. They include four strains affecting humans (229E, OC43, NL63 and HKU1); they are common all over the globe and they cause infections of the respiratory and digestive tract, which usually manifest with mild symptoms. The HCoV-229E and HCoV-OC43 strains are responsible for between 5 and 30% of these types of illnesses.

Novel human coronaviruses arose in the early 21st century, most likely as a result of animal viruses mutating to allow them to replicate within human cells.

The first was the severe acute respiratory syndrome (SARS) virus. SARS-CoV caused major concerns around the globe in 2002 and 2003, with over 8,000 confirmed cases and mortality rate of approx. 10%. It likely evolved from viruses affecting small insect-eating bats common in China.

Starting in 2012, around 2,500 cases of the Middle East respiratory syndrome (MERS, named after the region with the highest number of cases) were noted around the globe, with a mortality rate of approx. 35%. The virus also originally arose in animals, most likely camels, and person-to-person transmission is low.

We have recently seen the appearance of a third variant of the coronavirus.

Novel SARS-CoV-2 coronavirus

The first cases in humans were most likely noted in November 2019. The virus was initially named 2019-nCoV (novel coronavirus of 2019); its current official name is SARS-CoV-2. The International Committee on Taxonomy of Viruses (ICTV) chose the name due to the novel virus’s genetic similarity (79.5%) and the similarity of clinical symptoms resulting from SARS infections.

SARS-CoV-2 penetrates human cells using the same receptors as SARS-CoV. The receptor is the ACE-2 (angiotensin-converting enzyme 2) protein found in different locations in the body, including the lungs. This means that both strains are transmitted in a similar manner and cause similar symptoms.

The genome of the novel virus comprises 29,900 bases and has a close similarity (96%) to viruses isolated from bats found in China. It is highly likely that the virus originally passed from bats to humans, directly or indirectly. The process would have been accompanied by mutations allowing the virus to replicate in human cells. This means that history has repeated itself again, although this time we are dealing with new mutations and, as such, a novel virus. It is suspected that the virus has adapted along the way via different mammal species before reaching humans. Scientists have traced the SARS virus back to civets; SARS-CoV-2 is suspected to have come via pangolins, although it is unlikely this will ever be confirmed. In any case this has no practical relevance, since we are dealing with a human virus transmitted directly among people without any involvement of animals.

WHO named the disease caused by SARS-CoV-2 the coronavirus disease 2019 or COVID-19. While the name isn’t particularly original, it follows existing taxonomy. It is also important that the name does not implicate a particular region, country, population or animal species as the source while stressing that in clinical terms it is not the same as SARS.

COVID-19 symptoms

In the majority of cases, infected individuals show no symptoms at all or they are mild. Around 20% of patients experience severe acute clinical symptoms which may lead to complications and death.

Symptoms generally present within two to 14 days since exposure, with the majority of patients showing symptoms after five to six days.

The most common symptoms are fever, cough and shortness of breath. More severe cases can lead to pneumonia, respiratory failure and multi-organ failure. In some cases, this can lead to death.

Who is most at risk of infection and falling ill?

SARS-CoV-2 is mainly spread by small droplets produced when people cough. It is the same transmission route as flu and viral colds. We know that the virus replicates in cells of infected individuals, which means they can transmit it for several days before showing any symptoms. Furthermore, many people experience no symptoms, making them a potential hidden source of infection. All this means that it is extremely difficult to control and limit the spread of the disease.

Another important issue is dealing with the consequences of infection. This is where we see a high degree of variation. Analysis of tens of thousands of cases in China reveals that over 80% people experience mild symptoms and over 15% experience severe symptoms, with between 2 and 3% of cases resulting in death. It should be stressed that the majority of deaths occur in people with underlying medical conditions. The highest risk is associated with immunosuppression, cancer, diabetes and so on. People affected by these conditions are also at an increased risk of more familiar viruses such as flu.

It is currently difficult to state whether a particular group of patients is at a higher risk with the exception of elderly people: there is a clear correlation between age and severity of symptoms. Mortality rate increases with patient age. In people aged 50 and below, the mortality rate is a fraction of a percent, increasing to up to 20% in those aged 80 and above. Children appear to be less susceptible to COVID-19, as was the case with SARS.

It is currently unknown how many people are asymptomatic in spite of being infected. It is difficult to include them in epidemiology statistics since they require no medical assistance. As a result, the mortality rate reported currently is likely to be higher than reality; attempts to estimate the actual mortality rate for all age groups indicate a level of between 0.3 and 1%.

In comparison, human mortality rates for other diseases are estimated as follows: rabies – 100%, Ebola – 40-90%, H5N1 bird flu – 50%, smallpox – 20-50%, SARS – 10%, the Spanish flu of 1918 – 3-5%, measles – 2‰ and seasonal flu – 1‰.

Preventive measures

Coronaviruses are sensitive to basic disinfectants and high temperatures; therefore, standard disinfection procedures are recommended.

They include:

  • Washing hands with soap and water frequently; using alcohol-based sanitizing gels or liquid; avoiding touching the face, nose or mouth (a common habit which is almost impossible to control).
  • Covering the nose and mouth when coughing and sneezing; using disposable tissues and throwing them away immediately; sneezing into the crook of the elbow and never into palms.
  • Maintaining a distance of at least a meter from people exhibiting symptom of the disease.
  • Protective masks are generally not recommended for healthy individuals unless they are in close contact with people who are showing symptoms of infection with the novel coronavirus (for example as their care-givers); people with symptoms such as coughing or sneezing should also wear masks.

Treatment and vaccine

Treating patients suffering with COVID-19 is mainly symptom-based. There are currently no drugs registered specifically to target the coronavirus. Attempts to treat patients with antivirals indicate possible benefits of HIV protease inhibitors and neuraminidase inhibitors. However, both these drugs were developed to target different viruses. There are some reports on scientists discovering substances specifically targeting SARS-CoV-2, but any results are a long way off.

A clinical trial has been launched to assess the safety and efficacy of a novel antiviral drug, remdesivir, in patients infected with SARS-CoV-2. The compound is a nucleotide analog, disrupting the activity of viral RNA polymerases. It was previously tested in patients suffering from Ebola and the Marburg virus, and in SARS and MERS animal models. Another compound with a similar mechanism of action is favipiravir, currently undergoing clinical trials in China and Japan. However, neither of these drugs have been registered by the US Food and Drug Administration (FDA) to treat COVID-19.

A vaccine against COVID-19 is currently in development. The entire process of developing, standardizing and testing the compound before it can be brought into mass production takes a long time. It is estimated that a vaccine may be available in around 12 months.

Is it possible to eliminate the virus?

This question can be considered on the individual and population scales.

On an individual level, even at this stage of the pandemic thousands of people are already considered to have recovered. It is likely that they have developed an immunity, i.e. their bodies produce antibodies to the virus. This should lead to their bodies eliminating the virus and becoming resistant to infection in the future. However, there are worrying reports that some patients who have recovered from COVID-19 have tested positive for the virus again. We will only have the true picture by analyzing observations carried out over several months.

On the population scale, it seems extremely unlikely if not impossible to eliminate the virus completely, just as was the case with SARS. SARS-2 will likely remain one of the plethora of viruses affecting humans. Additionally, new mutations may change the course of infection in a direction we cannot currently predict.

Where can one find reliable information about the illness and disease?

  • National Institute of Public Health – National Institute of Hygiene
  • World Health Organization
  • European Centre for Disease Prevention and Control
  • Centers for Disease Control and Prevention
  • Coronavirus COVID-19 Global Cases by Johns Hopkins CSSE
  • ProMED International Society for Infectious Diseases

Authors:

  • Egbert Piasecki, PAS Ludwik Hirszfeld Institute of Immunology and Experimental Therapy in Wrocław
  • Brygida Knysz, Faculty and Clinic of Infectious Diseases, Liver Disorders and Acquired Immunodeficiencies at the Medical University in Wrocław
  • Image credit: Alissa Eckert, MS; Dan Higgins, MAM / Centers for Disease Control and Prevention’s Public Health Image Library (PHIL).