Covid app - positive tests soar again
But fewer pings per positive
The latest figures from the NHS Covid-19 contact tracing app are out - and once again they provide an intriguing snapshot of what’s happening with the virus and with our behaviour. Last week we saw a surprising fall in the number of contact tracing alerts sent out but a new record for positive tests entered into the app.
This time the figures for the week from the 30th December to the 5th January show a small uptick in contact tracing alerts sent to app users in England and Wales to 603,879 - still a high number but well short of the record set in mid-December when nearly 700,000 alerts were triggered.
But the figures for positive tests recorded in the app have soared again to 479,282 compared to 341,093 the previous week. And that means the ratio of positive tests to contact tracing alerts has fallen even further, down from 1.7 to 1.26 - in other words, the app is saying that every person who tests positive has previously been in close contact with just over one other user. In the summer at the height of the `’pingdemic” that ratio was a little under 5.
Last week I speculated that there were two possible reasons for this - that app users had been going out less and so coming into contact with fewer people, or that overall app use was down so that those who did have it switched on were less likely to encounter others.
After that post was published I was contacted by someone on the app team to say the first explanation was the right one - they pointed to Google mobility data showing a big decline in activity in mid-December as people started to worry about the impact of the Omicron variant.
These latest figures refer to infections that probably occurred over the Christmas period, when people were even less likely to be out and about. Certainly this data from London shows big declines in late December in the use of public transport and in visits to the office - though the latter is hardly surprising.
Maybe the story is just about people hunkering down at home, rather than abandoning the app - after all, there were over 260,000 new downloads in the latest week. But the plunging number of pings per positive test is still a bit of a mystery.