COVID-19 may be most contagious one to two days before symptoms appear
More than 4 in 10 coronavirus cases are spread by those not obviously sick, a study suggests
![SARS-CoV-2 infecting a cell](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2020/04/041520_ti_virus-shead_feat.jpg?fit=1028%2C579&ssl=1)
SARS-CoV-2, the coronavirus that causes COVID-19, appears to be most contagious at the start of an infection, before people even know they have it. Here, the virus (yellow) is shown infecting a dying cell (blue) from a COVID-19 patient.
NIAID/Flickr (CC BY 2.0)