Dr Michael Head, senior research fellow in global health at the University of Southampton, said: “Meeting indoors, particularly within the house of a friend or relative, increases the risks of transmission.
“There will be prolonged close contact, potentially over several hours. Rooms in households will be smaller and may be less well ventilated than in other larger indoors environments such as restaurants. There may be increased touching of shared objects, such as cutlery, and those meeting may well hug and kiss.
“All of these activities individually pose a small risk, but if enough low-risk activities take place, then the overall risk of transmission of Covid-19 increases.”
Professor Keith Neal, emeritus professor of the epidemiology of infectious diseases at the University of Nottingham, said transmission within households has been recognised as “one of the main routes of transmission from the earliest days of the pandemic”.
He said: “This is almost certainly due to the inability to keep distances within a house and the length of exposure time.
“Households mixing will lead to much more significant exposures (people closer together) and more time spent in contact than other areas where social distancing is easier (such as pubs and restaurants) and where masks are required (shops and public transport).
“Both degree of exposure and time spent are important.”
Prof Neal also commented on multi-generational families, saying: “It is the number of people in the household which is the key factor.
“Multi-generational families is about an increased risk in older people – who are more at risk of serious infection – acquiring Covid-19 from people they live with.”