What are the key points for understanding the dynamics of the COVID-19 ?
Text updated on 2021-06-20
We do not yet know everything about this recent COVID-19 epidemic but little by little, the data is accumulating. A few key findings provide insight into the dynamics of the epidemic, i.e., the number of cases, hospitalizations, and deaths related to COVID-19 depending on the weather, different countries and regions.
What we know
- The severity of the COVID-19 disease increases with age and certain co-morbidities. See the questions What factors increase the risk of dying from COVID-19 ? and Who are the vulnerable people?
- Has the care of patients with COVID-19 has improved since the beginning of 2020. Today, a patient COVID admitted to hospital is less likely to die from COVID-19. See the question Has the care of patients with COVID-19 improved?
- Children can have COVID-19 and are as contagious as adults. See questions Can my child pass on the COVID-19 ? and Children's role in the epidemic COVID-19 What do we know?
- Asymptomatic (symptom-free) people account for about 50% of cases and can transmit the coronavirus. See questions Can a person without symptoms infect others? and How many people are infected without showing symptoms?
- The peak of contagiousness is between 2 days before and 1 day after the onset of symptoms and contagiousness lasts about 10 days. See the question How long is a person contagious?
- Coronavirus is mainly transmitted by air through droplets (> 2.5-5 μm according to the authors) and aerosols (< 2.5-5 μm according to the authors) emitted through the nose and mouth (sputters) when coughing, sneezing, but also when breathing, speaking, eating, singing, shouting and through the eyes. See questions How is it COVID-19 is it caught? and Is the coronavirus SARS-CoV-2 transmitted by aerosols?
- On average and depending on the variants, an infected person transmits the virus to about 4-6 people in total if no masks are worn and to only one person if masks are worn. But in reality, the virus is mainly transmitted via super-propagation events/places, where one person transmits the virus to several dozen individuals. See the question Why are super-propagating situations crucial to understanding the COVID-19 ?
- It is possible to get the SARS-CoV-2 coronavirus a second time. See the question Can we catch COVID both times?
- The mask, when worn properly, helps to prevent contamination of other people. See the question Why put on a mask?
- Wearing a mask, by reducing the amount of virus received when infected, leads to a less severe form of the disease. See the question Does the severity of the disease COVID-19 depends on the dose of virus received?
- Heat, the sun, and outdoor locations limit the cases of transmission. See the questions Is the SARS-CoV-2 coronavirus resistant to sunlight? and Is the SARS-CoV-2 coronavirus resistant to cold or heat?
- In a naïve population that has not been in contact with SARS-CoV-2, up to 70-80% of individuals can be infected with the coronavirus. See question What is herd immunity and can it protect me from COVID-19 ?
What has not yet been fully established
- The proportion of people who are protected against the coronavirus SARS-CoV-2 because of a previous infection with SARS-CoV-2 or a related pathogen, and the duration of this immunity. See questions What is cross-immunity? Can it protect me from COVID-19 ? and Can you get COVID twice?
What we don't know yet
- The long-term sequelae of the disease and the evolution of the long forms of COVID .
- The best treatments for COVID-19.
- The effect of vaccination. At present, vaccines are available only in a small number of countries.
- The number of false positives and false negatives in serological and PCR tests, and thus the actual proportion of asymptomatic individuals who were infected with coronavirus.
- The threshold of positivity of qRT-PCRs to assert contagiousness
- The proportion of people who are protected against the coronavirus SARS-CoV-2 because of a previous infection with SARS-CoV-2 or a related pathogen, and the duration of this immunity. See question What is cross-immunity? Can it protect me from COVID-19 ?