How will we know if a second peak of Covid-19 has started?
The numbers to watch for any sign of a spike.
As lockdown measures start to be eased in each of the four nations of the UK, how soon might any impact of the changes show up in the daily numbers for coronavirus cases and deaths?
Because of the time it takes for someone to become infected with Covid-19 and for symptoms to appear, and for that person to then become ill enough to be admitted to hospital and either recover or die, there is a lag in all the data being reported.
Figures published in recent days showing the latest number of hospital admissions, patients and deaths all reflect the situation in the UK around three weeks ago – in other words, before the lockdown started to be eased.
Over the next week or so, enough time will have passed for any significant consequences of the changes introduced in England in the week beginning May 11 to start to appear in the figures.
That was the week in which people in England were cleared to spend more time outdoors, including unlimited exercise, to play sports with members of their own household, and to drive to outdoor open spaces irrespective of distance.
It was also the point at which workers who were unable to work from home were encouraged to resume travelling to work, if their workplace was open.
For evidence of how these changes may have affected the spread of coronavirus, the best place to look is at statistics that show what is happening in hospitals.
These figures provide a real-time, date-specific snapshot of what is occurring around England, and are not compromised by any discrepancy between when a hospital admission or death was reported and when it took place.
The number of Covid-19 hospital admissions in England is particularly useful as a “leading indicator” – in other words, an early sign of any impending change in the volume and severity of infections.
The latest figures show the number of admissions per day has fallen considerably since early April, has not been above 1,000 since May 2, and has been no higher than 600 since May 23.
The number of people in hospital with Covid-19 is another useful real-time measure. The publicly available figures are broken down by region, which helps give a more nuanced picture across England.
Seven regions are reported: the North West, North East/Yorkshire, the Midlands, eastern England, London, the South East and the South West. The latest figures show all regions have been on a broad downward trend for the past few weeks.
Then there are the figures showing the number of deaths of hospital patients in England who tested positive for Covid-19, broken down by the date the death occurred. It was from these figures that it was first possible to identify a peak in deaths on April 8.
The latest numbers show the daily number of deaths has not been higher than 600 since April 17, no higher than 400 since April 24, and no higher than 200 since May 8.
Care needs to be taken with this set of data, however. The totals are revised every day, often including previously uncounted deaths that took place several days or even weeks ago. This is because of the time it takes for deaths to be confirmed as testing positive for Covid-19, for post-mortem examinations to be processed and for data from the tests to be validated.
For example, there have been a few occasions recently when “zero” hospital deaths have been reported for a particular region of England, only to be revised upwards after a day or two.
These three sets of numbers – hospital admissions, patients and deaths – will all provide clues to what has happened since the lockdown was eased in England.
It may be that the changes are too minimal or gradual to show up clearly and quickly. And it could be that the more widespread changes to the lockdown in England, which came into effect on June 1, will have more of an impact – in which case we will need to wait until the end of June to see any consequences.
Scotland, Wales and Northern Ireland did not begin easing their lockdowns in quite the same way or at the same time as England, and it might take longer for any impact to show up in the data.
The latest available figures for hospital patients with Covid-19 in each of those nations show a trend that is either broadly downwards (Scotland) or has stabilised after a peak (Wales and Northern Ireland) – though the numbers are at a far lower level than the equivalent figures for England.
Finally, a word of warning about the numbers announced each day for confirmed cases of Covid-19, which are not always as useful as they seem. They are not real-time snapshots of the prevalence of coronavirus, due to the amount of time it takes for Covid-19 tests to be processed.
There are different levels of capacity for testing across the country and, as with hospital deaths, the numbers are often revised, so it is safer to look at long-term trends rather than day-to-day changes.
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