The WHO has urged countries to boost healthcare capacity and vaccinate their people to fight a surge in COVID-19 cases driven by the omicron variant, saying travel curbs could buy time but alone were not the answer.
"How worried should we be? We need to be prepared and cautious, not panic, because we're in a different situation to a year ago," Swaminathan said during an interview at the Reuters Next conference.
While the emergence of the new variant was unwelcome, she said the world was much better prepared given the development of vaccines since the start of the COVID-19 pandemic.
Much remains unknown about omicron, which was first detected in southern Africa last month and has been spotted in at least two dozen countries. Parts of Europe were already grappling with a wave of infections of the Delta variant before it emerged.
"We need to wait, lets hope it's milder ... but it's too early to conclude about the variant as a whole," Swaminathan said of what was known about omicron.
"Delta accounts for 99% of infections around the world. This variant would have to be more transmissible to out-compete and become dominant worldwide. It is possible, but it's not possible to predict."
The WHO's top scientist said the omicron variant seemed to be causing three times more infections than experienced previously in South Africa, meaning "it does seem to be able to overcome some of the natural immunity from previous infection".
Vaccines did appear to be having some effect.
"The fact that they're not getting sick .... that means the vaccines are still providing protection and we would hope that they would continue to provide protection," Swaminathan said.
Asked about the need for annual vaccine boosters, she said "the WHO is preparing for all scenarios", which could include an additional dose, particularly among some age groups or vulnerable sections of the population, or a modified vaccine.
"Natural infection acts as a booster," the WHO scientist said, adding that while the new variant "could have originated in a country where there isn't a great deal of genome sequencing", its origins were not known.
"We may never know," Swaminathan said.