World Health Organization through its spokesperson Dr. Margaret Harris said on Thursday that travel bans will not keep Omicron COVID-19 variant infections out of countries, but if they are put in place, they should be used well to buy time.

"Dr. Fauci is right that if you do do something as drastic as a travel ban, use it well to buy time," Harris said about the top U.S. infectious disease expert's comments about the effectiveness of temporary travel bans. "But we do know that it won't keep cases out. Usually, by the time where countries are aware that there is a risk of importation, that's already happened."

The duration of a travel ban should be used to ramp up surveillance, including looking at how and where people will be tested, and what will happen when there are positive cases, what the situation is in hospitals, how vaccination can be accelerated, and how to advise people and help them protect themselves, she added.

"The reason we're not keen on travel bans is not just because it harms the countries that you're shutting your borders to, but also it really limits the spread of critical things like the scientific materials you need, the humanitarian supplies you need to respond to something like this outbreak," Harris said.

She also spoke about how much of a time lag there is in countries that are thought to have Omicron and the countries that actually do.

"Probably there are many more countries, we expect, that already do have cases of SARS-CoV-2, the Omicron variant," she said. "It is simply a matter really of testing."

(With input from agencies)