The tube (subway) has been at half capacity for weeks.
If you're seeing photos of it being busy 'around the news and social media', it's either false, or TfL has overdone it in reducing service and so caused usual levels of crowding.
Excerpts from most recent service update email:
> Ridership on our services has fallen dramatically over the last few weeks.
> Some Tube stations that do not interchange with other lines will have to close until further notice
> From today, Friday 20 March, the Waterloo & City line will be closed and there will be no Night Tube or Night Overground services until further notice. Emirates Air Line will have a reduced service until 20:00 today
> From tomorrow, Saturday 21 March, Emirates Air Line will be closed until further notice
> From Monday 23 March, we will also gradually reduce other services across the TfL network
More here: https://tfl.gov.uk/campaign/coronavirus-covid-