What are the key points for understanding the dynamics of the COVID epidemic?

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?
• The management of patients with COVID-19 improved between early 2020 and June 2020. Today, a patient COVID admitted to hospital is less likely to die from COVID-19. See the question The management of patients with COVID-19 has it gotten any better?
• Asymptomatic people, both children and adults, can transmit the coronavirus. See the questions Can a person without symptoms infect others? and Can my child pass on COVID-19 ?
• 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?
• The coronavirus is mainly transmitted by airborne droplets (> 2.5-5 μm according to the authors) and aerosols (How is iCOVID-19 caught? and Is the SARS-CoV-2 coronavirus transmitted by aerosols?
• On average, an infected person transmits the virus to a total of about 3 people if no masks are worn and to only one person if they wear a mask. In reality, however, 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-propagative events crucial to understanding the COVID-19 epidemic?
• 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?
• 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 the question What is herd immunity and can it protect me from COVID-19 ? (not yet updated).

What has not yet been fully established

• Wearing a mask, by reducing the amount of virus received during contamination, would lead to a less severe form of the disease. See the question The severity of the COVID-19 disease.  Does it depend on the dose of virus received?

What we don't know yet

• The long-term sequelae of the disease. The first cases of the COVID-19 disease were postponed in China in December 2019, less than a year ago.
• The best treatments for COVID-19.
• The effect of vaccination. At present, vaccines are available only in a small number of countries.
• If children infect and transmit the coronavirus as much as adults. See the question Children's role in the COVID-19 epidemic: what do we know?
• 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 contagiousness of people without symptoms: how long does it last? What is its relative importance?
• The threshold of positivity of qRT-PCRs to assert contagiousness
• The proportion of people who are protected against SARS-CoV-2 coronavirus as a result of previous infection with a related pathogen SARS-CoV-2 or pathogen, and the duration of this immunity. See question What is cross-immunity? Can it protect me from COVID-19 ?