One swallow doesn鈥檛 make a summer, but the recent sustained fall in covid-19 cases in the UK may represent a turning point. However, experts warn there are many other explanations for the decline that cannot be ruled out.
The number of people in the UK testing positive for covid-19 has fallen for seven consecutive days, the longest sustained fall since daily cases started being recorded. According to , there were 23,511 new cases reported on 27 July, down from 46,558 on 20 July.
There are various possibilities for the fall, says at the University of Bath, UK, who keeps track of the numbers for the Independent SAGE group. 鈥淥ne is that genuinely infections are coming down because we鈥檝e peaked and hit the herd immunity threshold,鈥� he says. 鈥淚 don鈥檛 think many people think that is the case.鈥�
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at the Barcelona Institute for Global Health in Spain agrees: 鈥淎t some point, with a relatively high vaccination rate and so many people infected in parts of the UK, I expect herd immunity to be reached, but I am not sure it has been reached yet.鈥�
Cases may have fallen for other reasons. People may have been cautious in the face of rising cases, or socialising more outdoors, says Yates. Large numbers of people being asked to self isolate may also be driving transmission down, says at the University of Leeds, UK.
Another possibility is that cases aren鈥檛 actually falling but detection rates are. Government figures show that the number of tests being done has declined, dropping by 4.9 per cent in the week up to 22 July, the latest date for which figures are available.
Yates says this may be because people are on holiday, or are preparing to go on holiday and don鈥檛 want to be forced to cancel because of a positive test. There may also be a backlog, with some labs reportedly struggling to process all the tests that are coming in, he says.
Simon Clarke at the University of Reading, UK, says that vaccination may mean that infected individuals aren鈥檛 experiencing many symptoms and won鈥檛 have had a test. 鈥淚f we see an increasing number of double vaccinated people get infected, they鈥檙e seemingly less likely to have symptoms and won鈥檛 self-report,鈥� he says.
The completion of the Euro 2020 football tournament on 11 July may also be a factor. 鈥淚 do wonder whether we are just returning to where we would have been without the championships; the figures do show more men getting infected,鈥� says Clarke.
It is important to note that the impact of England removing most legal restrictions on gatherings and social distancing on 19 July has yet to feed into the numbers, as the average incubation period is five to six days. 鈥淭he daily test numbers will begin to see the effect towards the end of this week,鈥� says James Naismith at the University of Oxford.
Official figures are updated daily and the trend will be watched with interest. 鈥淲e would need seven to 10 days of decline to report that it is truly declining,鈥� says Lazarus.
Another data drop that will be watched closely is the weekly , which is published every Friday. The latest, on 23 July, found that UK infections were rising in the week ending 17 July. That, however, is a week behind the government figures. 鈥淲e need to look at the data as it comes out,鈥� says Yates.
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