Boris Johnson and Sir Keir Starmer clashed at Prime Minister’s Questions this week on the question of how many people are self-isolating properly after being asked to do so by NHS Test and Trace.
Calling for more government support for low earners, the Labour leader said: “It is estimated that only about 11 per cent of people self-isolate when they are asked to do so—11 per cent. That is not because they do not want to; it is because many do not feel that they can afford to do so.”
The prime minister, who is self-isolating himself, said: “In fact, the numbers that he gives for the success rate of the NHS self-isolation programme are, according to my information, way too low.”
The likely source for Keir Starmer’s figure of only 11 per cent isolating when asked to do so is this paper published by academics at King’s College London and University College London in September.
Looking at a string of surveys covering more than 30,000 people, the researchers found that 11 per cent “who reported having been alerted by the NHS contact tracing service and told they had been in close contact with a confirmed COVID-19 case… reported that they had not left home at all in the following 14 days”.
It was a bit higher for those who had reported experiencing symptoms of COVID-19 in the last seven days: 18 per cent said of these people said they had not left home since developing symptoms.
The authors of this paper stress that it is a pre-print, meaning it hasn’t gone through the peer review process yet, and that the data on people going into quarantine is likely to be revised and “should be treated with caution”.
Other studies from the earlier part of the pandemic came up with similar findings, according to a review of the evidence for the Scientific Advisory Group for Emergencies (SAGE) in September.
A YouGov poll carried out in May found that only 25 per cent of people who should have been self-isolating had not left their homes at all in the last 24 hours.
SAGE also reported that NHS Test and Trace had done a small telephone survey of people believed to have coronavirus and people who had been in close contact with them who were asked to self-isolate.
The headline figure sounded positive: 86 per cent of people with suspected Covid-19 and 89 per cent of their contacts said they had not left home at all in the last three days.
But it looks like about half the people the evaluation team tried to contact refused to take part in the survey. If we assume this is because they were not following the rules, “the team estimated that the lower bound estimate for adherence was 39 per cent”.
And even among people who said they were sticking to the rules, about 70 per cent reported doing a “final trip” before going into quarantine – which was actually a breach of the guidelines.
There is no link to any document in the SAGE documents here, which suggests that this is internal data shared with scientific advisors but not the general public. Without seeing the full results, it’s hard for us to make a judgement on it. In fact, we don’t even know when the phone survey was done.
How good is this kind of evidence overall? SAGE notes that surveys like this tend to give overly optimistic results, because people don’t want to admit that they have broken the rules.
On the other hand, the definition of breaking the rules on self-isolation might be too strict, making the picture too pessimistic. It would still count as a breach of quarantine if someone left their house briefly for a walk, for example, even if they were strictly avoiding other people and unlikely to pose an infection risk.
“Way too low”?
So while there are caveats to the 11 per cent figure Sir Keir quoted, SAGE agreed in September that adherence to the self-isolation rules was generally “low”.
What about Boris Johnson’s claim that – on the information he had been given – Sir Keir’s figure is “way too low”?
We asked the government what information the prime minister was relying on and a spokesman pointed us to evidence that Dido Harding, head of the Test and Trace programme, gave to the parliamentary committees on Science and Technology and Health and Social Care on November 10.
Baroness Harding said: “Some surveys we have run from the end of August through to the middle of September show 54 per cent of people telling us that they did not leave home during the period that they were asked to isolate. It is not 100 per cent, but it is slightly better than the other surveys. It is hard to put a finger on that.”
This appears to be internal data that is not in the public domain. In fact, Baroness Harding said that these statistics had not been checked for quality and she “hesitated to share it” with the committees.
On the face of it, an adherence rate of 54 per cent would represent a big recent improvement.
But as with the earlier Test and Trace survey mentioned by SAGE – which gave an overly positive headline figure – we would have to see all the data to put it in context.
Sir Keir Starmer’s figure for how many people are following self-isolation rules is backed by a scientific paper, but there are some caveats and the data is from several months ago.
Boris Johnson may have more recent figures, but they don’t appear to have been made public so we can’t FactCheck them properly.
It would be good to know whether people really are more likely to follow the guidelines now. That would tell us whether recent changes to policy, like making it a legal duty for people in England to self-isolate, and offering some financial support for low earners, have worked or not.
But we can’t find strong evidence either way at the moment.