All through the Covid-19 pandemic we have been hampered by a lack of data on just how many people have had the disease. Given that several studies have indicated that as many as 80 per cent of people who are infected show no symptoms whatsoever, it is extremely difficult to estimate this crucial figure – which determines the mortality rate of Covid-19 and also how far away we might be from achieving a position of herd immunity.
Today, however, comes some very substantial data. The Medical Research Council’s Biostatistics Unit has published estimates of infections derived from serological studies on samples collected from the NHS Blood Transfusion Service.
It estimates that between 4.9 million and 6.4 million people in England have antibodies showing they have already been infected. The median estimate is that ten per cent of the population of England have had the disease, varying from 17 per cent in London and 12 per cent in the North West, to seven per cent in the South East and four per cent in the South West. This higher than the estimate of 6.78 per cent published by the ONS last week – a figure derived from antibody tests.
These figures have allowed the MRC to calculate an Infection Fatality Rate (IFR) of 0.88 per cent for England as a whole. As with other studies, the figures show a dramatic rise in risk with age: from 0.001 per cent in the 5 – 14 age group to 23 per cent among the over 75s. The MRC estimates that at present 17,000 people a day are being infected. On the basis of an IFR of 0.88 and taking into account a lag between infection and death of around two weeks, it forecasts that deaths will be running at between 100 – 250 a day by mid-June. In fact, daily deaths are already in this region – 176 were recorded on Thursday. Given that infections and deaths have been on a downward trend for the past eight weeks we might expect deaths to have fallen a little lower than that by mid-June.
The MRC has also produced estimates for the ‘R’ rate for different parts of the country. These are a little higher than the range 0.7 to 0.9 per cent claimed by the government. They range from 0.9 in the Midlands, 0.94 in the South East and 0.95 in London to 1.0 in the South West and 1.01 in the North West. Many however, have questioned whether a single R rate means very much, given that it will vary considerably from that within hospitals and care homes to that in the community at large.
What the MRC can’t tell us, however, is how many of us are susceptible to infection with the disease. As has been noted here several times before, Covid-19 has shown a remarkable tendency to fade away once around one fifth of a population has been infected. On the Diamond Princess cruise ship, for example, only 17 per cent of the passengers and crew became infected in spite of the virus being able to run rampant in a closed environment for a fortnight. That is exactly the same proportion of Londoners who, according to the MRC, have already been infected.