How long are you contagious with Covid? Infectious period after positive test explained - when to self-isolate

The UK is in the grip of another surge of Covid infections as the Omicron BA.4 and BA.5 subvariants continue to spread.

The newest strains are more transmissible than previous Covid variants and are able to evade the immune protection built up by vaccines or previous infections, although experts say there is “currently no evidence” that they can cause more serious illness.

Latest figures from the Office for National Statistics (ONS) show a total of 2.7 million people had the virus in the week to 1 July, up from 18% the previous week.

It makes the highest estimate since late April, but is still below the record high of 4.9 million which was reached in late March during the wave of infections caused by the BA.2 strain.

Professor Tim Spector, the lead scientist behind the ZOE Covid Study, said he expects infection levels to continue increasing for another week before declining, but not to the same degree as previous waves.

He said that face masks and self-isolation are key to keeping infection levels down and urged people to stay at home if they have symptoms.

He said: “Wearing masks and isolating for a minimum of five days if you get the virus. If you’re not testing, you should assume it’s Covid at the moment because it’s far more prevalent than anything else out there.

“It’s much more likely to be Covid than a summer cold.”

If you do fall ill with Covid, here’s what you need to know about the contagious period and the latest guidance on self-isolation.

How long are you contagious with Covid?

Covid is spread via small droplets in the air and is easily transmitted through close contact with people who are infected.

It is spread when a person with the virus breathes, speaks, coughs or sneezes, and can be passed on even if someone does not have any symptoms.

It can also be picked up by touching surfaces where infected droplets have landed, so it is important to thoroughly wash your hands to minimise the risk.

People who have Covid can pass the virus to others from around two days before they start to display symptoms.

Those infected can then remain contagious for up to 10 days after symptoms appear, according to the UK government.

It is possible to spread the virus to others even if symptoms are mild, or non-existent, which is why you must self-isolate if you contract it.

When are you most infectious after a positive test?

Findings from a study published in The Lancet Microbe last year suggested that people are most infectious in the first five days after the onset of symptoms.

However, more recent research, published in JAMA Internal Medicine, found people are most contagious two days before and three days after they develop symptoms.

The European Centre for Disease Prevention and Control (ECDC) has said that adults with mild to moderate symptoms remain infectious no longer than 10 days after symptoms begin, regardless of the variant.

Adults with severe to critical illness, or severe immunosuppression, can still be contagious for up to 20 days after symptoms start.

The good news is that evidence suggests people who are fully vaccinated and contract Covid can have comparable amounts of virus in their body as someone who is unvaccinated, but they were less infectious overall.

How long do I need to self isolate?

The legal requirement to self-isolate after a positive Covid test ended across the UK earlier this year, with the governments instead asking people to take “personal responsibility”.

In England, it is recommended that you follow NHS guidance if you feel unwell. The NHS says you should stay at home and avoid contact with other people if you:

• have any symptoms of Covid and have a high temperature, or you do not feel well enough to go to work or do your normal activities
• have tested positive for Covid

If you have Covid you can pass on the virus to other people for up to 10 days from when your infection starts, although many people will no longer be infectious to others after five days. Those who test positive are urged to avoid meeting people at higher risk from Covid for 10 days.

If you live in Scotland, the Scottish Government recommends following the advice on NHS Inform.

If you test positive, you should stay at home and avoid contact with other people for five days after the day you took your test, or from the day your symptoms started (whichever was earlier).

If you have not tested positive, you should try to stay home until you feel better.

In Wales, you should self-isolate and order a test if you display Covid symptoms and continue to self-isolate until you get your result.

If the test is negative you can leave isolation immediately, but if it is positive you should isolate for five full days and then take another test, plus another the following day.

If both are negative you can leave isolation. If either one is positive, you should continue isolating until you get two negative results in a row, or until day 10, whichever is sooner.

In Northern Ireland, people are advised to isolate immediately if they have Covid symptoms or have tested positive.

If you display Covid symptoms you should self-isolate, order a test and remain in isolation until you get your result. If the test is negative you can leave isolation immediately.

If it is positive, you should stay at home and avoid contact with people for five days after the day of the test, or from the day symptoms started - whichever was earlier.

As children tend to be less infectious than adults, this period is reduced to three days for children and young people under the age of 18.