Vitamin D, explaining R and the 2 metre rule

R is one of the most important numbers of the pandemic. So what is it? And how is it estimated? We return to the topic of testing and ask again whether the governments numbers add up. As the government encourages those who can’t work at home to return to their workplaces, we’re relying on social distancing to continue to slow the spread of the virus. But where does the rule that people should stay 2 metres apart come from? And is Vitamin D an under-appreciated weapon in the fight against Covid-19?