A further 92,000 Covid cases were reported for England on Monday, a sharp rise on the previous day, after reinfections were included in the statistics for the first time.
Previously, daily Covid case figures – which reflect the number of new infections detected by testing – did not include reinfections for England, Scotland or Northern Ireland, although figures for the country of Wales have done so, provided the positive tests are more than 42 days apart. In other words, most people were only counted once even if they had caught Covid multiple times.
However, as the pandemic continues, the lack of reinfections in case data has raised concerns, with experts noting that prior infection offers little protection against Omicron, whereas – two years into the pandemic – there are more people who have had Covid at least once before.
The scientists noted that it was also important to include reinfections in order to understand the dynamics of the spread of emerging immune-evasive variants, while also shedding light on why some people may be repeatedly infected.
“It’s probably a combination of risk – from exposure – and the inherent likelihood of getting infected, once exposed,” said Professor Rowland Kao, an epidemiologist at the University of Edinburgh. “We need to know these things in order to better target interventions of different kinds – how important, for example, particular workplaces are likely to be, and how certain people are therefore going to be at greater risk.”
The new approach means reinfections will now be included in the daily Covid case figures for England and Northern Ireland, with such episodes defined as a positive specimen at least 90 days after the last – a discrepancy that captures the majority of reinfections but ensures those who simply shed the virus longer after an infection are excluded from the data.
Although data from the UK Health Security Agency suggests that some reinfections may occur within a shorter timeframe, this is a relatively small proportion of potential reinfections.
The Guardian understands that data for cases in Scotland will also include reinfections in the coming weeks, while data for cases in Wales will switch in the coming weeks to using the duration of the episode of 90 days of 90 days.
Under the current mixed definitions used, 92,368 new Covid cases were reported for the UK on Monday, down from 69,007 the previous day, with 81,720 reported for England alone compared to 59,559 on Sunday before reinfections were included.
The Guardian understands that reinfections were not initially included in daily case data across all UK countries because at the start of the pandemic it was unclear whether they were occurring and, whether reinfections were occurring. were producing, what was the interval between infections. While reinfection numbers have since been tracked by public health agencies and published in reports, daily case numbers have not – until now – included such episodes.
While including reinfections means the risk of lethality – the proportion of people reported as diagnosed with Covid who die – will decrease, Professor Sir David Spiegelhalter, a statistician at the University of Cambridge, warned the measure remains problematic.
“We have always known that the daily number of reported cases was a substantial undercount of the true number of infections – the ONS Covid Infection survey shows we need to at least double the daily number,” he said.
“Including reinfections will be an improvement and reduce the apparent case fatality rate, but no one should have taken this very seriously anyway. The case fatality rate is inevitably an overestimate of what is the best measure – the infection fatality rate, that is, the proportion of infected people who die, whether or not they become confirmed cases.