By Thomas Colson 

The World Health Organization's chief scientist, Dr. Soumya Swaminathan, has urged people to be cautious with their behavior even after receiving a COVID-19 vaccine.

Swaminathan told a Monday briefing there was not yet enough evidence from vaccine trials "to be confident that it's going to prevent people from actually getting the infection and therefore being able to pass it on."

She added that at least for now, even people who had received the vaccine should still quarantine when traveling to countries with lower coronavirus transmission rates.

Vaccine researchers in the US are trying to determine whether vaccines can stop the virus from spreading or are effective only at preventing symptomatic cases of COVID-19.

The World Health Organization is urging even people who have received a coronavirus vaccine to quarantine when they travel because there is not yet evidence that vaccines prevent people from transmitting the virus.

WHO's chief scientist, Dr. Soumya Swaminathan, noted on Monday that the agency had not established whether the COVID-19 vaccines being administered across the US and in Europe prevented people from getting the virus and passing it to others.

"At the moment I don't believe we have the evidence of any of the vaccines to be confident that it's going to prevent people from actually getting the infection and therefore being able to pass it on," Swaminathan told a virtual briefing.

Swaminathan was responding to a question about whether vaccinated people should still be required to quarantine when traveling to countries with lower transmission rates.

"I think until we know more, we need to assume that people who have been vaccinated also need to take the same precautions until there is a certain level of herd immunity that's been built in the population," she said.

Last month it was reported that vaccine researchers in the US hoped to determine whether vaccines could stop the virus from spreading or whether they prevented only symptomatic cases of COVID-19.

The answer to that question is significant, as a vaccine that prevents so-called asymptomatic transmission would help protect more than just the people who receive the shots.

Dr. Larry Corey, a virologist who is planning one study to answer that question, said last month that the study still needed funding as well as cooperation from the pharmaceutical companies that had developed effective vaccines.

Three vaccines in the West have been found effective in large trials in preventing recipients from becoming ill or seriously ill with COVID-19.

Two of those, the Pfizer-BioNTech vaccine and the Moderna vaccine, are already being administered in the US and in Europe. The third, developed by AstraZeneca and Oxford University, is likely to receive approval in the UK within days, according to the Financial Times.

Moderna's chief medical officer, Tal Zaks, said last month that he believed it was likely the vaccine would prevent transmission but warned that there was not yet "sufficient evidence" of it.

"When we start the deployment of this vaccine we will not have sufficient concrete data to prove that this vaccine reduces transmission," he said.

"I think it's important that we don't change behavior solely on the basis of vaccination."