COVID-19 Disease

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COVID-19 – Disease

The WHO declared COVID-19 a public health emergency of international concern, the highest level of alarm under international law, on January 30, 2020 and a pandemic on March 11, 2020. Since then, the COVID-19 pandemic continues to move at record speed.



View dashboards that provide an up-to-date overview on the geographic distribution of
COVID-19 cases worldwide:
View an up-to-date overview on the distribution of COVID-19 cases in Germany:

1. What is COVID-19?

COVID-19 (coronavirus disease 2019) is defined as illness caused by the newly discovered coronavirus SARS-CoV-2. It was initially reported to the World Health Organization (WHO) on December 31, 2019.

Coronaviruses (CoV) represent a large family of viruses which may cause illness in humans ranging from the common cold to serious illness. The most recently discovered coronavirus (SARS-CoV-2) caused the current global pandemic, which now poses major challenges to almost all countries in the world.[1] The coronavirus is named after its shape caused by the protruding spike proteins on its surface that are relevant for the interaction with human cells. Corona meaning crown in Latin.

Most people infected with SARS-CoV-2 will experience mild to moderate respiratory illness and recover without requiring special treatment. However, serious illness can also develop, including fatal multi-organ failure.

The coronavirus and how it spreads in the human body


The spreading of the virus inside one’s body starts with the virus particle attaching to cells that carry a receptor called ACE2. This allows the virus to enter the cell where it releases its viral genetic code and forces the cell to produce virus proteins. These proteins create new coronaviruses and are released into the body.

Although COVID-19 is seen as a disease that primarily affects the lungs, it can damage many other organs as well. These include, for example, the heart (e.g. myocarditis), brain (e.g. headache, anosmia, dysgeusia, disturbance of consciousness, and seizures), liver (e.g. liver dysfunction) and kidneys (e.g. kidney dysfunction or failure). It is not yet possible to predict the extent to which this organ damage may also increase the risk of long-term health problems. A newly identified syndrome linked to SARS-CoV-2 is the multisystem inflammatory syndrome in children (MIS-C), also known as paediatric inflammatory multisystem syndrome (PIMS). MIS-C is a rare systemic disorder involving persistent fever and extreme inflammation following exposure to SARS-CoV-2, the virus responsible for COVID-19.[1]

Additionally, asymptomatic patients may have long-term health problems. Given that SARS-CoV-2 is highly infectious, a key challenge of the COVID-19 pandemic is to reduce the spread of SARS-CoV-2 infections. Current evidence suggests that the virus is mainly transmitted through respiratory droplets and contact routes. In the absence of social distancing measures, it can spread more efficiently. SARS-CoV-2 can be transmitted from one person to another very early in the course of the disease when patients have mild or no symptoms. The extent of asymptomatic infections in the community is currently unknown.

2. What are the symptoms of SARS-CoV-2?

Presentation of COVID-19 may range from asymptomatic or very mild SARS-CoV-2 infection, up to severe and potentially fatal disease. Symptoms usually develop two days to two weeks following exposure to the virus.

Gastrointestinal complaints such as nausea, vomiting and diarrhoea may also occur. However, this list is not exhaustive and other less common symptoms have been reported. Even mild symptoms from SARS-CoV-2 infection can last for weeks, or disappear only to rebound with renewed intensity. Pneumonia appears to be the most common serious acute manifestation of the disease. Some people need hospitalization for supplemental oxygen or mechanical ventilation.

Main symptoms include:

  • fever or chills
  • cough
  • shortness of breath or difficulty breathing
  • fatigue
  • muscle or body aches
  • loss of taste or smell

3. COVID-19 risk groups

Most people recover from COVID-19 without needing hospital treatment. COVID-19 related severe illness have mostly involved older individuals (≥60 years), and persons who have underlying health conditions (e.g., diabetes, cardiovascular disease, chronic pulmonary disease, cancer, hypertension, obesity, chronic kidney disease). These people have an increased risk for needing hospital-based treatment such as oxygen supplementation. However, anyone, including young people, can catch COVID-19 and become seriously ill.

It is estimated that 349 million people, about 4% of the global population, are at high risk of severe COVID-19 and would require hospital admission if infected. Interestingly, about 6% of males are expected at high risk compared with 3% of females.[2]

In Germany, the cumulative proportion of patients who were hospitalized was reported to be 17%, although hospitalization rates vary from country to country globally.[3]

»About one in five individuals worldwide could be at increased risk of severe COVID-19 due to underlying health conditions[2]

Age of patients admitted to hospital in Germany for COVID-19[3]

An observational study with more than 10,000 patients who were treated for COVID-19 disease in hospital showed the following: 17% received mechanical ventilation, of whom 24% were aged 18–59 years, 22% were aged 60–69 years, 31% were aged 70–79 years, and 23% were aged ≥80 years.[3]

Proportion of patients with comorbidities hospitalised in Germany for COVID-19[3]

4. How can you prevent the spread of COVID-19 and protect yourself?

People's behaviour can be a key factor in how easily the virus that leads to COVID-19 spreads from one person to another. As far as we know today, SARS-CoV-2 mainly spreads via respiratory droplets that are transmitted from person to person who are in close contact. When released in respiratory secretions (e.g. when coughing, sneezing, speaking, singing) the virus can infect other people through contact with mucous membranes.
The virus may also persist on surfaces for varied durations and can be spread by contact with a surface, although this is not believed to be the main route of transmission. People can become infected by touching these objects or surfaces, then touching their eyes, nose or mouth. This is why it is important to wash your hands regularly with soap and water or clean with an alcohol-based hand rub.

Some simple precautions recommended by the World Health Organisation (WHO)

  • Maintain at least a 1-meter distance between yourself and others to reduce your risk of infection when they cough, sneeze or speak.
    • Maintain an even greater distance between yourself and others when indoors. The further away, the better.
  • Make wearing a mask a normal part of being around other people.
  • Avoid the 3Cs: spaces that are closed, crowded or involve close contact.
    • Outbreaks have been reported in restaurants, choir practices, fitness classes, nightclubs, offices and places of worship where people have gathered, often in crowded indoor settings where they talk loudly, shout, breathe heavily or sing.
    • The risks of getting COVID-19 are higher in crowded and inadequately ventilated spaces where infected people spend long periods of time together in close proximity.
  • Meet people outside. Outdoor gatherings are safer than indoor ones, particularly if indoor spaces are small and without outdoor air coming in.
  • Avoid crowded or indoor settings but if you can’t, open a window. Increase the amount of ‘natural ventilation’ when indoors.
Go to WHO site
© Drazen Zigic -
© Konstantin Yuganov -

And don’t forget the basics of good hygiene:

  • Regularly and thoroughly clean your hands with an alcohol-based hand sanitizer or wash them with soap and water. This eliminates germs including viruses that may be on your hands.
  • Avoid touching your eyes, nose and mouth. Hands touch many surfaces and can pick up viruses. Once contaminated, hands can transfer the virus to your eyes, nose or mouth. From there, the virus can enter your body and infect you.
  • Cover your mouth and nose with your bent elbow or tissue when you cough or sneeze. Then dispose of the used tissue immediately into a closed bin and wash your hands. By following good ‘respiratory hygiene’, you protect the people around you from viruses, which cause colds, flu and COVID-19.
  • Clean and disinfect surfaces frequently especially those which are regularly touched, such as door handles, faucets and phone screens.

Contribute to containing the spread of COVID-19 by observing the DHM formula: distance - hygiene - mask!

Check out a video from WHO:
Check out a video from GAVI, the Vaccine Alliance:
Find out more information about COVID-19 advice for the public:

5.    The importance of community immunity and vaccination in a pandemic situation

Pandemics such as COVID-19 spread quickly from one community to another. One method for preventing or stopping this spread besides physical distancing and hygiene measures, is for a significant percentage of the population to be immune in order to achieve so-called community immunity (also known as “herd” immunity). Community immunity occurs when a large portion of a community becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected.

»Simple calculations suggest that herd immunity to SARS-CoV-2 requires 60-70% of the population to be immune.«[4]

Paths to community immunity

There are two paths to community immunity:

  • when enough persons are protected after having received a vaccination or
  • when a lot of persons have gone through the disease (mass infection).

The benefit of community immunity is that persons which cannot be vaccinated or have a weaker immune system – like babies, pregnant women or cancer patients – are indirectly protected as the virus does not spread as easily because most individuals are immune. However, to achieve community immunity a high number of persons must be immunised to interrupt the chain of transmission.

In contrast, achieving natural community immunity through mass infection may be challenging in a disease like COVID-19, given its high rates of severe symptoms and deaths and the consequent overburdening of health systems. This is why community immunity is generally pursued through vaccination programmes. Once community immunity has been achieved, the disease can eventually be overcome. For example, smallpox was eradicated with a collaborative global vaccination program.

Naive population: Outbreak quickly emerges

Herd immunity*: Virus fails to spread and persist in the population

Successful transmission

Unsuccessful transmission



Susceptible individual

Susceptible but indirectly protected individual

* 70% of the population is immune

Adapted from Randolph, HE Immunity 2020[5]

How do vaccines work?

Vaccines work to stimulate the body's own immune response, so that this immune response can occur promptly in the event of an infection. Usually, the vaccine contains a harmless part of a virus that triggers your body to produce antibodies and memory cells, but does not make you sick. Later on, when you experience an infection with the virus, your body already has circulating antibodies that immediately start to eliminate the virus. The memory cells recognize the virus and ensure fast production of even more antibodies. Viruses like SARS-CoV-2 may be fought early and quickly in the body so that COVID-19 does not occur. The goal of a vaccine is to help to prevent from the infectious disease caused by SARS-CoV-2. Scientists around the world are working to develop vaccines against COVID-19.

Find out more information about vaccination at:


  1. Abrams JY et al. Multisystem Inflammatory Syndrome in Children (MIS-C) Associated with SARS-CoV-2: A Systematic Review. J Pediatr 2020; doi: 10.1016/j.jpeds.2020.08.003 [Epub ahead of print]
  2. Clark A et al. Global, regional, and national estimates of the population at increased risk of severe COVID-19 due to underlying health conditions in 2020: a modelling study. Lancet Glob Health 2020; 8: e1003–17
  3. Karagiannidis C et al. Case characteristics, resource use, and outcomes of 10 021 patients with COVID-19 admitted to 920 German hospitals: an observational study. Lancet Respir Med 2020; 8: 853-862
  4. Gomes MGM, Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold, medRxiv preprint doi:
  5. Randolph HE and Barreiro LB. Herd immunity: understanding COVID-19. Immunity 52:737-741.

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