The World Health Organisation's chief scientist warns that even as numerous countries start rolling out vaccination programs to stop COVID-19, herd immunity is highly unlikely this year.
At a media briefing on Monday, Dr Soumya Swaminathan said it was critical countries and their populations maintain strict social distancing and other outbreak control measures for the foreseeable future.
In recent weeks, Britain, the US, France, Canada, Germany, Israel, the Netherlands and others have begun vaccinating millions of their citizens against the coronavirus.
"Even as vaccines start protecting the most vulnerable, we're not going to achieve any levels of population immunity or herd immunity in 2021," Swaminathan said.
"Even if it happens in a couple of pockets, in a few countries, it's not going to protect people across the world."
Scientists typically estimate that a vaccination rate of about 70 per cent is needed for herd immunity, where entire populations are protected against a disease. But some fear the extremely infectious nature of COVID-19 could require a significantly higher threshold.
Australian Associated Press