It's a critical question that has played on the minds of individuals with COVID-19 who want to see friends and relatives again.
There isn't a universally accepted answer so far.
In the US, government rules allow most people to end isolation after five days without having to take a test, while the UK only allows people with COVID-19 to leave after two days of isolation. They have to wait ten days for a test.
Policymakers have to balance the need to limit the advance of the Pandemic with the need to stop the economy from grinding to a halt. The US COVID-19 isolation guidelines were designed to get people back to jobs, according to President Biden's chief medical advisor.
In the UK and the US, disease experts warn that isolation guidance doesn't follow science, and that people who haven't taken a test are at risk of spreading the disease.
On January 14, Robert Wachter, a professor and chair of the department of medicine at the University of California, San Francisco, said that his son's rapid test was positive at Day 10. He said that if they hadn't tested, he would be on his second day of work.
The UK Health and Security Agency estimated that almost a third of people with COVID-19 were still contagious five days after symptom onset or a positive test. According to the models, only a small percentage of people who were isolated for five days and tested negative were still infectious. The data shows that 5% of people are infectious after ten days.
People with COVID-19 can be infectious from two days before symptoms to ten days after.
If the UK guidance is followed, there is a good chance that a patient won't be infectious anymore, but it isn't perfect. He said that everyone is a bit different.
The estimates are not specific to Omicron infections.
At the time of the data release, Lawrence Young told Insider that there wasn't a lot of data on the dynamics of an Omicron infection. We can't predict how infectious someone is.
The UKHSA data was the best available to guide what to do if you don't know if you're infectious or not, but it wasn't perfect for every case.
Other early data.
A study of 21 people who were hospitalized with Omicron found peak levels of infectious virus particles three to six days after diagnosis. The study authors said that no infectious virus particles were found after 10 days.
The United Kingdom.
A study published in the International Journal of Infectious Diseases found that 3% of participants carried potentially infectious virus particles at day 10. They said that some people retained their levels for up to 69 days. Omicron became the most common variant before the study was done.
The number of days people are infectious in the community could be cut to almost zero by requiring at least two consecutive days of negative tests, according to scientists from the London School of Hygiene and Tropical Medicine. The number of days after initially testing positive is irrelevant.
The models used pre-Omicron data. The study has not been published or reviewed by other experts.
People with Omicron infections have lower peak virus particles levels than people with Delta infections. James Hay, the study lead from the Harvard T.H. Chan School of Public Health, cautioned that the methods used don't necessarily predict infectiousness.