Europe and the US have suspended rollouts of the Johnson & Johnson vaccine after American authorities revealed six cases of blood clots from more than six million vaccinations.

Australian officials are watching the cases closely, despite the federal government confirming on Tuesday it would not seek to buy the Johnson & Johnson vaccine.

That’s because J&J’s vaccine mechanism of using a cold virus to deliver the instructions to cells to fight COVID-19 is the same as that used by AstraZeneca’s vaccine.

Health Minister Greg Hunt revealed on Tuesday that Australia would not buy any doses of the Johnson & Johnson’s vaccine because it is “the same type of vaccine as the AstraZeneca vaccine”.

Amid growing evidence of blood clot risks, the AstraZeneca vaccine is no longer the preferred jab for those under 50.

Overnight (Australian time), US health agencies recommended pausing the use of Johnson & Johnson’s COVID-19 vaccine as the company announced a delay of its rollout in Europe.

European regulators said last week they were reviewing rare blood clots in four recipients of the Johnson & Johnson vaccine in the US.

Acting US Food and Drug Administration Commissioner Janet Woodcock said on Tuesday night (US time) the agency expected the pause to only last a few days. It is intended to provide information to healthcare providers on how to diagnose and treat the clots.

The move came after six women under 50 developed rare blood clots after receiving the shot.

European regulators said earlier in April they had found a possible link between AstraZeneca’s COVID-19 vaccine and a similar rare blood clotting problem that led to a handful of deaths.

Immunology experts echoed US officials in underscoring that the risk posed by the J&J vaccine appeared extremely low and it remained a valuable tool against COVID-19.

The FDA said there had been one reported death from the rare blood clotting condition among recipients of the J&J vaccine. Another person was in a critical condition.

FDA official Peter Marks said it was “plainly obvious” the J&J cases were “very similar” to the AstraZeneca ones.

However, officials said there had been no similar blood clot cases reported among recipients of the Moderna or Pfizer-BioNTech vaccines, which use a different technology.

The J&J and AstraZeneca vaccines both use an adenovirus vector – a harmless cold virus – to deliver instructions for human cells to produce a protein found on the surface of the coronavirus, spurring the immune system to recognise and attack the actual virus.

Among leading global COVID-19 vaccine developers, China’s CanSino Biological and Russia’s Gamaleya Institute with its Sputnik V vaccine also rely on this approach.

The Pfizer-BioNtech and Moderna vaccines use messenger RNA (mRNA) technology.

The federal government said 40 million doses of the imported Pfizer vaccine should be available in Australia by the end of 2021, on top of local supply of the AstraZeneca version.