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AstraZeneca COVID-19 vaccines sit in storage at Region Hovedstaden's Vaccine Center in Copenhagen, Denmark, on Feb. 11, 2021.POOL/Reuters

Denmark on Wednesday became the first country to stop using AstraZeneca’s COVID-19 vaccine altogether, following news of its possible link to very rare blood clot cases, health authorities said.

The decision will push back the scheduled conclusion of Denmark’s vaccination scheme to early August from July 25, they said.

Results of investigations into the blood clots “showed real and serious side effects,” health agency head Soren Brostrom said in a statement.

“Based on an overall consideration, we have therefore chosen to continue the vaccination programme for all target groups without this vaccine.”

The European Union’s drug watchdog said last week it had found a possible link between the AstraZeneca vaccine and cerebral venous sinus thrombosis (CVST), a brain blood clot, but said the risk of dying from COVID-19 was “much greater” than the risk of mortality from rare side effects.

Moderna, Pfizer, AstraZeneca or Johnson & Johnson: Which COVID-19 vaccine will I get in Canada?

Canada pre-purchased millions of doses of seven different vaccine types, and Health Canada has approved four so far for the various provincial and territorial rollouts. All the drugs are fully effective in preventing serious illness and death, though some may do more than others to stop any symptomatic illness at all (which is where the efficacy rates cited below come in).

PFIZER-BIONTECH

  • Also known as: Comirnaty
  • Approved on: Dec. 9, 2020
  • Efficacy rate: 95 per cent with both doses in patients 16 and older, and 100 per cent in 12- to 15-year-olds
  • Traits: Must be stored at -70 C, requiring specialized ultracold freezers. It is a new type of mRNA-based vaccine that gives the body a sample of the virus’s DNA to teach immune systems how to fight it. Health Canada has authorized it for use in people as young as 12.

MODERNA

  • Also known as: SpikeVax
  • Approved on: Dec. 23, 2020
  • Efficacy rate: 94 per cent with both doses in patients 18 and older, and 100 per cent in 12- to 17-year-olds
  • Traits: Like Pfizer’s vaccine, this one is mRNA-based, but it can be stored at -20 C. It’s approved for use in Canada for ages 12 and up.

OXFORD-ASTRAZENECA

  • Also known as: Vaxzevria
  • Approved on: Feb. 26, 2021
  • Efficacy rate: 62 per cent two weeks after the second dose
  • Traits: This comes in two versions approved for Canadian use, the kind made in Europe and the same drug made by a different process in India (where it is called Covishield). The National Advisory Committee on Immunization’s latest guidance is that its okay for people 30 and older to get it if they can’t or don’t want to wait for an mRNA vaccine, but to guard against the risk of a rare blood-clotting disorder, all provinces have stopped giving first doses of AstraZeneca.

JOHNSON & JOHNSON

  • Also known as: Janssen
  • Approved on: March 5, 2021
  • Efficacy rate: 66 per cent two weeks after the single dose
  • Traits: Unlike the other vaccines, this one comes in a single injection. NACI says it should be offered to Canadians 30 and older, but Health Canada paused distribution of the drug for now as it investigates inspection concerns at a Maryland facility where the active ingredient was made.

How many vaccine doses do I get?

All vaccines except Johnson & Johnson’s require two doses, though even for double-dose drugs, research suggests the first shots may give fairly strong protection. This has led health agencies to focus on getting first shots to as many people as possible, then delaying boosters by up to four months. To see how many doses your province or territory has administered so far, check our vaccine tracker for the latest numbers.

As of April 4, the European Medicines Agency had received reports of 169 cases of CVST after 34 million Astrazeneca doses had been administered in the European Economic Area.

The EU regulator, however, left it to individual states to make their own risk assessments and decide how to administer the vaccine.

Many countries in Europe and elsewhere have resumed administering the shot, with some restricting its use to certain age groups, mostly those aged above 50 or above 60.

Denmark was the first country to initially suspend all usage of the vaccine in March over safety concerns, and has also put Johnson & Johnson’s vaccine on pause pending further investigations into a possible similar blood clot link.

Almost one million of the country’s 5.8 million population have received their first shots, 77 per cent getting Pfizer-BioNTech’s vaccine, 7.8 per cent Moderna’s and 15.3 per cent AstraZeneca’s.

Denmark is in the process of easing restrictions after its daily COVID-19 infection rate slowed to 500-600 from several thousand in December.

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