Australia has opted against purchasing Johnson & Johnson’s coronavirus vaccine as it investigates another blood clot event linked to the Oxford-AstraZeneca shot, which uses similar technology known as viral vector.

Second thoughts about that technology have prompted Australia to abandon its goal of inoculating its entire adult population by year end.

The nation of about 25 million people had pinned its coronavirus immunization drive on the vaccine jointly developed by British-Swedish firm AstraZeneca and Oxford university, but the government has since limited the vaccine’s use because of links to rare blood clot disorders both in Australia and in Europe, particularly among younger people.

As a result, Australian authorities say they do not plan to acquire any more viral vector vaccines, including those from Johnson & Johnson.

The European Union’s drug regulator said last week that it was launching a review of possible links between the Johnson & Johnson vaccine and four cases of serious blood clots reported in the United States and another unspecified country.

“J&J is another viral vector vaccine, and we have no advice recommending, at this point, that the government purchase any additional viral vector vaccine,” Australian Health Minister Greg Hunt told reporters Tuesday, the Associated Press reported.

“That’s not a reflection, that’s simply an observation,” he said, adding the government was following the advice of Australia’s scientific and technical advisory group.

On Tuesday, federal health agencies in the United States released a statement recommending a pause in J&J vaccinations as officials look into six cases of a rare type of blood clot among the 6.8 million patients who had recently received the vaccine. All six patients were women under the age of 50.

In Australia, officials have opted instead for additional doses of the vaccine jointly developed by U.S. pharmaceutical giant Pfizer with German biotech firm BioNTech to immunize younger Australians, but that won’t arrive until later this year.

The Australian government has said Pfizer will be the recommended vaccine for those 50 years and younger, but the AstraZeneca vaccine will still play a key role in the country’s vaccination drive.

“The most vulnerable people in our community are not just over 50, they are actually a lot older than that,” Prime Minister Scott Morrison said last week. “The AstraZeneca vaccine is well suited to address those critical vulnerable groups.”

Australia has recorded two blood clot cases that its health regulator says could be linked to the Oxford-AstraZeneca vaccine, including a man who received the shot last month. The second case involving a woman in her 40s was reported this week.

The woman checked into the hospital around two weeks after her first vaccination, Australian Broadcasting Corp. reported.

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