Scientists in Australia have called for a halt to the rollout of the AstraZeneca vaccine, claiming recent data has cast doubt on the inoculation’s ability to create herd immunity.

The scientists pointed to data from a study published in the Lancet last month that found the British-Swedish vaccine had only 62 percent efficacy, compared with over 90 percent for the Pfizer-BioNTech alternative.

A large-scale trial in the UK and Brazil reported a 62 percent effectiveness for those who were vaccinated with two full doses of the AstraZeneca vaccine.

Australia has already purchased 53 million doses of the AstraZeneca vaccine, however.