Despite more than two billion vaccine doses against COVID-19 given worldwide, the World Health Organization recommended Friday that people keep wearing masks to help prevent the transmission of coronavirus.

"The vaccines we have are very good at preventing severe disease, or death, if you get infected with the virus," WHO spokeswoman Margaret Harris told journalists at a UN briefing in Geneva when asked why people should continue wearing masks despite being vaccinated or having had COVID-19 in the past.

The WHO says that some 2.16 billion vaccine doses have been administered worldwide, with more than 174 million confirmed cases of the virus and almost 3.8 million deaths recorded.

"What we want is to reduce the transmission. And we don't know that the vaccines can prevent the transmission," said Harris.

"So, wearing your mask is about preventing the transmission where you're in close contact, or where you're in crowds, or where you're in a confined space, and you can't get out of that confined space."

Scientists do not know whether somebody who is vaccinated can still have the virus and still transmit it, while they need to learn more about different variants.

"We want to limit every opportunity for any of the variants to transmit themselves," said Harris.

She said wearing the mask and following all the other public health measures, avoiding crowds and closed spaces, doing everything people can to be outside, and really ventilating the room are needed.

Harris said scientists do not know whether the vaccines can help bring down the transmission.

"We think they do help, but that they will not do everything. So that's why we asked you to do the other things."/aa