People who test positive for coronavirus or show symptoms in the UK must now self-isolate for at least 10 days, rather than seven.
The change, announced by the UK’s chief medical officers, comes as ministers try to avoid a resurgence of the virus.
Until now, those showing key symptoms – a new continuous cough, a temperature or loss of taste or smell – have had to self-isolate for at least a week.
The new advice is in line with World Health Organization guidance.
The chief medical officers said the change is “particularly important to protect those who have been shielding and in advance of the autumn and winter when we may see increased community transmission”.
Evidence shows that people with Covid-19 have “a low but real possibility of infectiousness” between seven and nine days after falling ill, they said.
People are most contagious just before they first display symptoms and for the first few days afterwards. But scientists say evidence that they could pass it on up to nine days later has “strengthened”.
Advice on the length of isolation varies between countries. For example, the Irish Republic says those who have symptoms should isolate for 14 days, while in the US those with symptoms are told to isolate for 10 days and can only leave isolation if they have had at least 24 hours without a fever.
It comes after the prime minister warned of signs of a “second wave” of the pandemic in parts of Europe.
Speaking on BBC Breakfast before the announcement, Health Secretary Matt Hancock said the government wanted to “take a precautionary approach” and “protect people from that wave reaching our shores”.
Frank Atherton, chief medical officer for Wales, said the change was “vital” and “nobody should be under the illusion that coronavirus has gone away”.
- England death rate among worst in Europe
- What’s the evidence Europe is having a ‘second wave’?
- UK signs deal for 60 million virus vaccine doses
The government has also confirmed that registered health and care professionals travelling to the UK from high-risk countries will be required to self-isolate for 14 days. An quarantine exemption for health professionals had been in place since June.
Official figures published on Thursday showed that 43,119 people who tested positive for Covid-19 in England had their cases transferred to NHS Test and Trace since its launch in May.
The tracing system successfully contacted just over 77% of these – but just over 23% were not reached.
The figures, from the Department of Health and Social Care, also showed that of 222,589 people identified as close contacts of those who tested positive, 83% had been reached and asked to self-isolate.
Prime Minister Boris Johnson’s pledge – that by the end of June everyone tested in person would receive results within 24 hours – is still not being met, with about three-quarters (76.4%) of people getting results on time in the week up to July 22.
For those using home testing kits, 76.9% received results within 48 hours.
But the government is concerned that some people are not coming forward for testing, hampering its ability to track outbreaks, because they wrongly think they have to pay for it or that they are not eligible.
What are the rules on self-isolating?
Self-isolating means staying at home and not leaving it.
Anyone who has either tested positive for coronavirus or shown symptoms should isolate themselves for at least 10 days, and those who show symptoms should arrange to get tested.
- a new continuous cough
- a high temperature
- a loss of, or change in, your normal sense of taste or smell
They should continue to self-isolate if they still feel unwell after that initial period.
Other members of their household should isolate for 14 days and not leave their homes.
If you test positive you will be contacted by contact tracers, who will establish who else you might have passed on the infection to.
Anybody they deem to be at risk will have to isolate themselves for 14 days from the point of contact.