As reported last week, coronavirus restrictions will be eased over Christmas to allow people to mix with a slightly wider circle of family and friends. Between 23 and 27 December, three households in a “Christmas bubble” can mix indoors and stay overnight.
However, the risk of unwittingly inviting someone who is infected into your family gathering rises sharply with the numbers present. The Georgia Institute of Technology together with Stanford University in the US has produced a website which enables individuals to calculate the risk based on their location and the numbers in their group at https://covid19risk.biosci.gatech.edu/. For groups of 20 meeting in Cambridge, 2 out of 25 such groups would expect to have at least one infected person. Risk of infections may be reduced by frequent handwashing, face coverings, social distancing and meeting outside or with good ventilation inside.