The maths behind estimations

So how did the scientists calculate the estimated total number of district Covid infections?

Prof Michaelis and Dr Wass say the standard approach would be to find out how many people have antibodies. But current systemic data on this is not available.

They say Covid-19 antibody levels appear to decrease quickly “in a significant fraction of Covid survivors”. Meanwhile, the number of positive tests recorded is not a reliable indicator as there will have been many cases that will never be formally diagnosed.

They add: “However, deaths are hardly ever missed, and there are reliable data that estimate the infection-fatality rate for Covid-19, i.e. the percentage of infected people that die from the disease, is between 0.5% and 1.5%.” According to the most recent figures, there have been 281 Covid deaths in the Canterbury district.

For an infection-fatality rate of 1.5%, this results in 18,733 infections (11% of the district’s population). For an infection-fatality rate of 0.5%, this results in 56,200 infections (34% of the population). The average infection-fatality rate in high-income countries like the UK is 1.15%, according to researchers from Imperial College London.

Under this measure, about one in seven people (15%) in the Canterbury district would have already caught coronavirus. So far, 8,075 of the district’s residents (5%) have tested positive for Covid. But there was far less testing during the first wave last Spring than there is today. Health secretary Matt Hancock has said about one in three people with coronavirus are asymptomatic, highlighting the need for those without symptoms to visit rapid testing centres.