Despite incredible efforts by scientists around the world, there is still much we do not understand, and we are all now part of a planet-wide experiment trying to find answers.
Here are some of the big outstanding questions.
Children can definitely catch coronavirus. However, they mostly develop mild symptoms and there are relatively few deaths among children compared with other age groups.
Children are normally super-spreaders of disease, partly because they mix with lots of people (often in the playground), but with this virus, it is not clear to what extent they help spread it.
The virus emerged in Wuhan, China, at the end of 2019, where there was a cluster of cases at an animal market.
The coronavirus, officially called Sars-CoV-2, is closely related to viruses that infect bats, however it is thought the virus was passed from bats to a mystery animal species that then passed it on to people.
That "missing link" remains unknown, and could be a source of further infections.
Colds and flu are more common in the winter months than in the summer, but it is not yet known whether the warmer weather will alter the spread of the virus.
The UK government's scientific advisers have warned it is unclear whether there will be a seasonal effect. If there is one, they think it is likely to be smaller than that for colds and flu.
If there is a major dip in coronavirus over the summer, there is a danger that cases will spike in winter, when hospitals are also having to deal with an influx of patients with the usual winter bugs.
Covid-19 is a mild infection for most. However around 20% go on to develop more severe disease, but why?
The state of a person's immune system seems to be part of the issue, and there may be some genetic factor too. Understanding this could lead to ways of preventing people from needing intensive care.
There has been much speculation but little evidence on how durable any immunity to the virus is.
Patients must have built up an immune response, if they successfully fight off the virus. But as the disease has been around for only a few months there is a lack of long-term data. Rumours of patients being infected twice may be down to tests incorrectly saying they were free of the virus.
The question of immunity is vital for understanding what will happen in the long term.
Viruses mutate all the time, but most alterations to their genetic code do not make a significant difference.
As a general rule, you expect viruses to evolve to be less deadly in the long run, but this is not guaranteed.
The concern is that if the virus mutates, then the immune system no longer recognises it and a specific vaccine no longer works (as happens with flu).
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