Australia recommended that AstraZeneca’s Covid-19 shots should not be administrated to people under 60 on Thursday, a fresh blow to the country’s slow vaccine rollout.

Health Minister Greg Hunt said concerns over possible links to blood clots meant Pfizer was now “the preferred vaccine” for everyone under 60 years old.

Australian authorities had already prohibited providing AstraZeneca shot to those over 50 in April, after several cases of severe blood clots were possibly linked to it.

Thursday’s further restriction came after a 52-year-old woman died of blood clotting after receiving the vaccine.

Hunt admitted the move would “challenge” the country’s already badly stalled vaccine rollout, which has seen just three percent of its population of 25 million fully vaccinated so far.

Facing growing public disquiet over the slow rate of jabs, the conservative government also announced Thursday that a senior army officer, Lieutenant General John Frewen, would lead the federal vaccine rollout, now dubbed operation “Vaccine Shield”.

The move is likely to have a marginal impact, as responsibility for inoculations has largely fallen to Australian states.

Australia has invested heavily in the AstraZeneca vaccine, developing a facility to produce 50 million doses locally.

Purchases of other shots have been more limited and have faced multiple delays, forcing the government to abandon its target of vaccinating all adults by September this year.

Australia has only a few locally transmitted cases of COVID-19 and has closed its borders to all but a handful of foreign travelers.

Those measures are likely to stay in place until a large percentage of adults are inoculated, but in the meantime the virus has repeatedly jumped from hotel quarantine facilities into the community, sparking lockdowns and costly restrictions.