Johnson & Johnson has said it will delay the roll-out of its Covid-19 vaccine in Europe after US authorities moved to suspend use of the shot due to health concerns.

The move is likely to affect Ireland's vaccination plan as around 600,000 doses were due to be delivered to the country before the end of June.

The US Food and Drug Administration and the Centers for Disease Control moved to "pause" the one-jab Covid-19 innoculation on worries over six reported cases of a rare type of blood clot in the US.

"We have made the decision to proactively delay the roll-out of our vaccine in Europe," J&J said, adding that it was reviewing the cases with European health authorities.

In a statement, J&J said it is aware of an extremely rare disorder involving people with blood clots in combination with low platelets in a small number of people who received its vaccine.

It said: "Out of an abundance of caution, the CDC and FDA have recommended a pause in the use of our vaccine.

"In addition, we have been reviewing these cases with European health authorities. We have made the decision to proactively delay the roll-out of our vaccine in Europe."

European officials have said J&J began delivering its vaccine to EU countries yesterday and had committed to delivering 55 million doses to the bloc by the end of June and another 120 million in the third quarter.

The first batch of J&J vaccines has been expected in Ireland around 19 April. About 600,000 doses were due to be delivered here before the end of June.

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The European medicines watchdog said it was aware of a decision by its US counterpart to pause the administration of the Johnson & Johnson vaccine.

In a statement, the European Medicines Agency said it is not clear there is a link between the vaccine and the incidents and its safety committee is continuing a review announced last week.

Earlier, European Commission Spokesperson for Health Stefan De Keersmaecker said the commission is "looking to matters and will react as soon as possible".

Speaking on RTÉ's Drivetime, he would not be drawn on whether the delay would affect the company's compliance with its contract with the EU.

"We always knew that the delivery order on the production division of vaccines was going to be a challenge, and this is a process that normally takes ten years, which is one of the reasons why we have contracts with different companies in our portfolio approach."

When asked whether recent issues with AstraZeneca and today’s decision by J&J would prompt the implementation of a "contingency plan" by the EU, Mr De Keersmaecker said the objective of the EU remains to have enough vaccines for 60-70% of the adult population by the end of the second quarter.

"Let's not speculate on scenarios. We have received 108 million doses in the first quarter.

"The objective is 360 million doses in the second quarter, which would allow us to ensure the vaccination of 60 to 70% of the adult population of European citizens.

"This is what we're working towards. That's the objective, that's the focus.

"On the basis of the deliveries that we expect in for the second quarter, we should be in a position to reach the 70% target," he said.

WHO 'monitoring' global database

The World Health Organization said it is monitoring the global database of adverse affects related to the vaccine to see if there have been cases anywhere else.

It said it was watching the situation closely and was waiting for the FDA and EMA reports.

The move comes a week after European regulators said they had found a possible link between AstraZeneca's Covid-19 vaccine and a rare blood clotting problem that had led to a small number of deaths.

J&J's single dose vaccine - most Covid-19 shots are delivered over two doses - and AstraZeneca's low-cost vaccine are seen as vital tools in the fight against a pandemic that has claimed more than three million lives.

An advisory committee to the CDC will hold a meeting tomorrow to review the cases linked to the J&J vaccine, and the US FDA will review the analysis, the agencies said in a joint statement.

All six recipients were women between the ages of 18 and 48, and the symptoms occurred six to 13 days after vaccination.

In the cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia).

The CDC and FDA said the adverse events appeared to be extremely rare.

One death among six reported cases

J&J said it was working closely with regulators and noted no clear causal relationship had been established between the events and the Covid-19 vaccine made by its Janssen unit.

One woman died and a second in Nebraska has been hospitalised in critical condition, the New York Times reported, citing officials.

As of yesterday, more than 6.8 million doses of the J&J vaccine had been administered in the United States.

J&J's shares were down 3% before the opening bell.

White House Covid-19 response coordinator Jeff Zients said the J&J decision will not have a significant impact on the country's vaccination plan and was taken out of "an abundance of caution".

"This announcement will not have a significant impact on our vaccination plan: Johnson & Johnson vaccine makes up less than 5% of the recorded shots in arms in the United States to date," Mr Zients said in a statement.

The US move comes less than a week after Europe's drugs regulator said it was reviewing rare blood clots in four people in the US who had received the shot.

Europe's drugs regulator continues to recommend the use of AstraZeneca's Covid-19 vaccine, saying the benefits outweigh the risks.

Several EU countries, however, have limited its use to certain age groups.

Ireland's National Immunisation Advisory Committee has recommended that the AstraZeneca vaccine be limited to people over 60 years of age.

Australia has no current plans to add J&J's coronavirus vaccine to its immunisation drive, authorities said, as it moves away from procuring vaccines under review fo rpotential links to blood clots.

S Africa suspends J&J vaccine roll-out

South Africa has suspended its roll-out of the Johnson & Johnson Covid-19 vaccine.

The announcement delays an already sluggish vaccination campaign in Africa's worst-hit country, which has so far only administered the US-made jab.

"We have determined to voluntarily suspend our roll out until the causal relationship between the development of clots and the Johnson & Johnson vaccine is sufficiently interrogated," Health Minister Zweli Mkhize announced in an online press briefing.

Mr Mkhize said that although no blood clots had been reported among vaccinated citizens in South Africa, the FDA's advice should not be taken "lightly".

"We hope that the deliberations will only take a few days," he added.

"Given the preliminary literature at hand our scientists are confident that the FDA decision is only on a precautionary basis, and we expect that this will not result in the complete withdrawal of the Johnson & Johnson vaccine."

South Africa has vaccinated just under 290,000 health workers since 17 February.

The second phase of the country's roll-out plan, which will target essential workers and over-60s, is scheduled to begin on 17 May.

Authorities had already been forced to scrap plans to start vaccinating with the Oxford/AstraZeneca jab after a study suggested the formula was less effective against a dominant local virus strain.

So far, South Africa has secured 31 million doses from J&J and 30 million from Pfizer, which are yet to be delivered.

Another 1.2 million doses will be donated by the international vaccine sharing facility Covax, and an undisclosed amount from the African Union.