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Thromboembolic and bleeding risk has been cited by a number of countries in halting use of AstraZeneca's COVID-19 vaccine, but the company and health agencies argued against a causal link.

Denmark and Norway were first to stop administering AstraZeneca's vaccine last week over isolated cases of bleeding, blood clots, and low platelet count. Others followed.

Germany and France on Monday became the latest to announce a . Germany cited seven cases of cerebral vein thrombosis among patients getting one of the 1.6 million AstraZeneca shots given there so far. German Health Minister Jens Spahn call this a but above average if confirmed to be linked to the vaccine.

Norwegian public health officials over the weekend reported three more cases of blood clots or brain hemorrhages in 30- to 40-year-olds after vaccination, which spurred to join in. The jumped in over the weekend, pointing to its own 10 cases of serious events, including possible thrombosis or embolism but no thrombocytopenia.

and have banned certain batches of the vaccine after isolated sudden deaths and thrombotic events in recently-inoculated people.

In a released Sunday, AstraZeneca said it has seen no evidence of increased risk of pulmonary embolism, deep vein thrombosis, or thrombocytopenia either overall or for specific age groups, genders, batches, or particular countries.

It said there had been 15 deep vein thrombosis (DVT) events and 22 pulmonary embolism (PE) cases reported among the some 17 million recipients of its vaccine in the European Union and U.K. as of March 8.

"This is much lower than would be expected to occur naturally in a general population of this size and is similar across other licensed COVID-19 vaccines," it said.

AstraZeneca also pointed to the clinical trials in which, "even though the number of thrombotic events was small, these were lower in the vaccinated group. There has also been no evidence of increased bleeding in over 60,000 participants enrolled."

The European Medicines Agency (EMA) reemphasized that there is .

It too pointed to no apparent bump in rates compared with the general population. As of March 10, it has received a report of 30 cases of thromboembolic events among close to 5 million people who got the AstraZeneca shot in the European Economic Area.

In fact, the lower rate than in the general population may even suggest that the vaccine protects against thrombosis, and certainly reducing the disease reduces thrombosis from it, Mary Cushman, MD, medical director of the University of Vermont Medical Center Thrombosis and Hemostasis Program in Burlington.

Even so, there are concerns that slowing down vaccination -- AstraZeneca's vaccine has accounted for around a third of inoculations in Europe -- will cost lives and could contribute to hesitancy.

"I do worry that some people will not be able to differentiate between an unrelated or coincidental VTE [venous thromboembolism] occurrence (due to DVT/PE being so common in the general population) and a causative relationship," Stephan Moll, MD, of the division of hematology at the University of North Carolina at Chapel Hill, told MedPage Today.

Soumya Swaminathan, MD, WHO chief scientist, noted that it has happened before: Norway early on raised concerns about deaths among the elderly getting vaccinated, but then clarified it was only the expected rate of death.

Of the some 300 million doses of all COVID vaccines administered globally, not a single death has been documented to have been caused by vaccination, she pointed out. "We do not want people to panic. We would for the time being recommend that countries continue vaccinating with AstraZeneca."

has said it continues to back AstraZeneca's vaccine. The company is expected to apply for emergency use authorization in the U.S. in the coming weeks, once its U.S. phase III trial results become available.

The EMA has an ongoing review of clotting risk with the AstraZeneca shot that is expected to yield more information when it meets Tuesday, with its monthly safety report coming out this week too. WHO's advisory committee on vaccine safety has been monitoring the data in close contact with the EMA and also will meet Tuesday.

"This does not necessarily mean these events are linked to vaccination, but it's routine practice to investigate them," WHO Director-General Tedros Adhanom Ghebreyesus, PhD, said at a press briefing Monday. "It shows that the surveillance system works and effective controls are in place."

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