I was having an argument with an anti-vaxxer friend. He told me that the household transmission rate is roughly 12%. I looked this up and sadly he appears to be right. I have attached an image which comes from twitter.com/kallmemeg/status/1451828458544369667?s=20 . (Sad because every time he is right about something he takes that as more evidence that he is right to be an anti-vaxxer). However, I am not sure I really understand what "household transmission rate" or "secondary attack rate means".
Does this mean that if one person gets covid and lives in a house with 3 others, say, then there is only a 1 in 8 chance that any of the others in the house get covid? This sort of stats is not my strong point. My personal experience is that it is rare for only one person to be infected in a house so this 12% figure seems very surprising if it is really true.