Getting an initial course of COVID-19 vaccines to unprotected groups all over the world should remain a top priority before offering booster shots to vulnerable groups, World Health Organisation (WHO) Emergency Director Mike Ryan said on Tuesday.

A major study on Tuesday found that two doses of Pfizer-BioNTech's COVID-19 vaccine appear to have given 70% protection against hospitalization in South Africa in recent weeks, suggesting weaker efficacy against the new Omicron variant.

"People are always asking should we be going for a primary vaccination or boosters, the reality is we should be doing both. We should be focusing on getting those who are unvaccinated vaccinated as quickly as possible and then being able to give booster doses to those in vulnerable groups," Ryan told an online event.