We’ve seen an apparent fall in the number of people testing positive for Covid-19 in the UK over the last week or so.

It’s welcome news, though puzzling, as many scientists expected case numbers to rise following the gradual lifting of lockdown restrictions.
What is going on? No one knows for sure, but here are some of the main theories.

It could be a statistical blip

Public Health England figures from across the UK show the number of positive cases has fallen significantly since a peak on July 17.

But no data set is perfect, and some scientists are sceptical that the official UK government figures are capturing the number of positive cases accurately.

There’s no sign of a similar fall in cases in the ZOE Covid study. These alternative figures suggest that the number of infections is still rising.

We’ll have to wait to find out if survey data due to be published by the Office for National Statistics on Friday also shows a fall in cases.

‘Freedom Day’ effect hasn’t shown up yet

Most of the remaining restrictions were lifted in England on July 19, and we would not expect the effects of this final unlocking to show up in the data yet.

Professor James Naismith from the University of Oxford, Director of the Rosalind Franklin Institute, said: “For me the next milestone will be the ONS data release on Friday 21st August, we will know for sure the effect of the end of the lockdown.

“It is important to understand that the daily test numbers will only begin to see the effect of the end of lockdown towards the end of this week.

“Many scientists, myself included, expect the end of lockdown to see a rise in cases. However, we have been wrong before and we will be wrong in the future.”

Less social contact than expected

Studies have shown that people dramatically cut their social contacts during the early lockdowns, and continued to be cautious after restrictions were lifted.

Google data suggests that visits to most shops and offices and the use of public transport is still well below pre-pandemic levels.

The recent spell of hot weather may also have encouraged outdoor rather than indoor mixing, and it has been widely reported that large numbers of people have been self-isolating in recent weeks after being “pinged” by the NHS Covid-19 app.

Professor Adam Finn from the University of Bristol said: “Self-evidently, many people are still making an effort to avoid becoming infected and infecting others, helped by the recent sunny weather that keeps us all outside.”

We were too pessimistic

While some scientists predicted a large third wave of infections, all efforts to model the future trajectory of the pandemic are prone to uncertainty and big margins of error.

In fact, many models projected a similar pattern: a fall in cases over the summer, with factors like warmer weather and the school holidays helping to reduce the chances of infection.

Professor Karl Friston from University College London, who sits on the Independent SAGE panel, said: “From a dynamic causal modelling perspective, the recent fall in case rates is unremarkable. This kind of modelling predicts the current resurgence of infections will peak around now, with no further surges until winter.

“It may be that people have been over interpreting the worst-case scenario modelling from the SPI-M (advisory group) that suggested a hundred thousand cases per day over the summer.”

Vaccination is working

We would expect the UK’s high vaccination levels to help cut the rate of Covid transmission, especially if people remain cautious about mixing socially at the same time.

However, as FactCheck reported last week, scientists are generally cautious about what the vaccination programme can realistically achieve.

Despite the clear benefits of vaccines in reducing transmission of the virus, serious illness and death, experts think it’s unlikely that we have vaccinated enough people yet to reach the threshold of “herd immunity” that would see the virus go into permanent decline.