GENEVA, Switzerland –The World Health Organization said on Wednesday that slashing the mandatory isolation period for people with Covid-19 was a trade-off between controlling transmission and keeping economies up and running.

Spain said it would shorten the quarantine for positive cases from 10 to seven days, after US health authorities on Monday halved the recommended isolation time for people with asymptomatic infections from 10 to five days.

The WHO said governments were struggling to find the right balance, following an 11 percent surge in cases around the world last week as the Omicron variant spreads.

“If people shorten the quarantine period, there will be a small number of cases that will develop disease and potentially go on to transmit, because they have been let out of quarantine earlier,” WHO emergencies director Michael Ryan told a news conference.

“But that will be a relatively small number, and a lot of people who won’t transmit will also be released from that quarantine.

“So it is a trade-off between the science and being absolutely perfect in what you try to do, but then having the minimal disruption that you can possibly have to your economy and society — and governments are struggling to find that balance.” The WHO’s guidelines on quarantine are, for symptomatic patients, 10 days after symptom onset, plus at least three additional days without symptoms; and for asymptomatic cases, 10 days after a positive test.

Ryan said the average incubation period so far has been around five or six days — but there was a range.

The likelihood of someone developing symptoms after five, six or seven days goes down exponentially, he explained, adding that it was then for governments to make the judgement call on when to allow people out of isolation.

“There is some data to suggest that the incubation period for Omicron may be shorter, but there will still be a very wide range,” he said, stressing that this was based on very limited studies.

“It would be advisable at this point if we don’t see huge shifts, huge moves in reducing control measures for Covid-19 purely on the basis of initial or preliminary studies.”