When Johnson &amp; Johnson’s single-dose coronavirus vaccine was authorized for emergency use in late February, ​it was seen as a breakthrough for reaching vulnerable and isolated Americans, a crucial alternative to vaccines that require two shots weeks apart and fussier storage. It was soon popular on college campuses, in door-to-door campaigns and with harder-to-reach communities that often struggle to access health care.

But with only 11.8 million doses administered in the United States — less than 4% of the total — the “one and done” vaccine has fallen flat. States have warned for weeks that they may not find recipients for millions of doses that will soon expire, partly because the vaccine’s appeal dropped after it was linked to a rare but serious blood-clotting disorder and injections were paused for 10 days in April.

The vaccine took another hit last week, when regulators told Johnson &amp; Johnson that it should throw out tens of millions of additional doses produced at a plant in Baltimore because they might be contaminated. The diminished supply and enthusiasm for the shot mean that its role in the United States is fading fast, even though millions of Americans have yet to be vaccinated.

“It’s just not what I think anybody would have hoped it would be when it came out,” said Dave Baden, chief financial officer of the Oregon Health Authority.

Health officials in a number of other states presented a similarly discouraging picture. The pause on the Johnson &amp; Johnson vaccine, they said, effectively kicked it aside for good; only about 3.5 million doses have been used since the pause was lifted April 23. Kim Deti, a spokesperson for the Wyoming Health Department, said the graph of uptake in her state told the vaccine’s story: a significant climb in the early weeks of its rollout, followed by a plateau that began around the pause.

State officials had initially hoped the Johnson &amp; Johnson shot would be a workhorse: a versatile, easy-to-store tool they could stockpile at mass vaccination sites, quickly reaching thousands of people they would not need to track down for a second dose. But after demand dropped, their goals grew more modest.

It is being used in a smaller-bore fashion this week at the Fiesta festival in San Antonio, the College World Series in Omaha, Nebraska, a Juneteenth celebration in Johnstown, Pennsylvania, and an aquarium in Long Beach, California. At a food bank in Reno, Nevada, 12 doses of the Johnson &amp; Johnson vaccine were administered Thursday, said Jocelyn Lantrip, director of marketing and communications for the Food Bank of Northern Nevada.

Between the small number of doses distributed and the lack of interest in them, public health experts say, the United States missed a critical opportunity to address health disparities with a vaccine that should have been ideal for reaching vulnerable populations. Dr. Chip Riggins, a regional medical director who oversees vaccine events in south central Louisiana, said that few organizers requested the shot anymore, even in a state with one of the lowest vaccination rates in the country.

“In the early days of J&amp;J, working with the African American community and the churches, the faith community here, it was a very, very popular option,” Riggins said. “It pains me that it isn’t being accepted like it was before the pause.”

Dr. José R. Romero, the Arkansas health secretary, called the shot’s fast decline a “lost opportunity” for reaching the vulnerable in his state.

“This is a vaccine that was very well-suited for populations where we have problems getting into,” he said. “We’re now at the point where it’s five people or three people; it doesn’t matter, we’ll open a vial.”

Riggins said he had limited success in recent months sending the vaccine to churches, casinos and even gas stations, including one in LaPlace, Louisiana, where organizers offered the shot Thursday. An international crew on a ship was elated to receive their shots last weekend, Riggins said. But not being able to fully protect more people with just a single dose, he added, was hindering the state’s progress.

Johnson &amp; Johnson’s decline in the United States has dovetailed with decreasing demand for COVID vaccines overall. Nearly 30 million doses of the Pfizer-BioNTech vaccine are sitting unused, as are about 25 million of Moderna’s. But a total of 135 million people have been fully immunized with those vaccines, 11 times more than with Johnson &amp; Johnson’s. The two-dose vaccines have a higher efficacy rate overall — roughly 95% versus 72% for Johnson &amp; Johnson’s — but studies showed that all three were highly effective at preventing hospitalization and death.

Alex Gorsky, Johnson &amp; Johnson’s CEO, said last week that he was still hopeful that the vaccine, which has been used in 26 countries, would help contain the pandemic overseas. The company has promised up to 400 million doses to the African Union. Separately, COVAX, the global vaccine-sharing program, is supposed to receive hundreds of millions of doses.

“We still believe that this is going to be a very important tool in the overall armamentarium,” Gorsky said at an event hosted by The Wall Street Journal.

But manufacturing problems at a factory in Baltimore run by Emergent BioSolutions, Johnson &amp; Johnson’s subcontractor, have had serious consequences for the vaccine. Because of a major production mishap that resulted in a two-month shutdown in operations, Johnson &amp; Johnson has essentially been forced to sit out the brunt of the pandemic in the United States while Pfizer and Moderna, the other federally authorized vaccine makers, provided almost all the nation’s vaccine stock.

Johnson &amp; Johnson has had to throw out the equivalent of 75 million doses, and the regulatory authorities in Canada, South Africa and the European Union also decided to pull back millions more doses made at the Baltimore plant. The company has been able to deliver less than half of the 100 million doses it promised the federal government by the end of this month.

Dr. Anne Zink, Alaska’s chief medical officer, said that in her state, Johnson &amp; Johnson’s shot had become a victim of its own timing. By late February, when it was authorized by the Food and Drug Administration, Alaska had figured out how to get two-dose vaccines to remote areas, leaving the one-shot regimen less crucial than she had initially imagined.

Dr. Clay Marsh, West Virginia’s COVID-19 czar, said that the pause and Johnson &amp; Johnson’s later authorization — more than two months after Pfizer’s and Moderna’s — deprived it of a “halo effect.” By the time West Virginia had an ample supply of all three vaccines, he said, “people started to get this concept that maybe there’s something better about being immunized with Pfizer and Moderna.”

The Johnson &amp; Johnson shot had also suffered from a “social network effect,” said Andrew C. Anderson, a professor of public health at Tulane University who researches vaccine hesitancy. Most Americans who were inoculated in the early months of the vaccine campaign received Moderna and Pfizer shots, and so their friends and family were less likely to deviate and accept a different brand.

In Louisiana, hospitals in the New Orleans area have started offering the Johnson &amp; Johnson shot to people on their way out of the emergency room; the thinking is that people will be more likely to accept the vaccine when a doctor who has treated them asks them to take it. And in Arkansas, where only one-third of the population is fully vaccinated, state officials are offering Johnson &amp; Johnson doses to agriculture, manufacturing, wastewater and poultry workers, with gift certificates for hunting and fishing licenses as a reward.

“I don’t think that the book on J&amp;J is closed,” said Dr. Joseph Kanter, Louisiana’s top health official. “It’s just not going to be a game changer.”

In West Virginia, officials are now hoping to use up some 20,000 doses of the shot at summer fairs and festivals and in parks, Marsh said. And in Oregon, Baden, the state health authority official, said that providers were working to exhaust about 150,000 doses in correctional facilities and higher-throughput sites in Portland. The sharp drop in interest, he said, was “tragic.”

Onisis Stefas, chief pharmacy officer at Northwell Health, New York state’s largest health care provider, said he was still working through the system’s original allocation of Johnson &amp; Johnson from March — a sign that demand had shriveled long ago. Doctors’ offices have asked for as few as 10 doses at a time instead of the pack of 50 the vaccine typically comes in.

In Michigan, where more than 200,000 Johnson &amp; Johnson doses sit unused, officials are racing to redistribute the vaccine to high-volume sites in hopes of administering them before they expire.

“It’s just kind of one after another negative news about the vaccine,” said Dr. Joneigh S. Khaldun, the chief medical executive in the state.

When Johnson & Johnson’s single-dose coronavirus vaccine was authorized for emergency use in late February, it was seen as a breakthrough for reaching vulnerable and isolated Americans, a crucial alternative to vaccines that require two shots weeks apart and fussier storage.

When Johnson & Johnson’s single-dose coronavirus vaccine was authorized for emergency use in late February, it was seen as a breakthrough for reaching vulnerable and isolated Americans, a crucial alternative to vaccines that require two shots weeks apart and fussier storage. It was soon popular on college campuses, in door-to-door campaigns and with harder-to-reach communities that often struggle to access health care. But with only 11.8 million doses administered in the United States — less than 4% of the total — the “one and done” vaccine has fallen flat. States have warned for weeks that they may not find recipients for millions of doses that will soon expire, partly because the vaccine’s appeal dropped after it was linked to a rare but serious blood-clotting disorder and injections were paused for 10 days in April. The vaccine took another hit last week, when regulators told Johnson & Johnson that it should throw out tens of millions of additional doses produced at a plant in Baltimore because they might be contaminated. The diminished supply and enthusiasm for the shot mean that its role in the United States is fading fast, even though millions of Americans have yet to be vaccinated. “It’s just not what I think anybody would have hoped it would be when it came out,” said Dave Baden, chief financial officer of the Oregon Health Authority. Health officials in a number of other states presented a similarly discouraging picture. The pause on the Johnson & Johnson vaccine, they said, effectively kicked it aside for good; only about 3.5 million doses have been used since the pause was lifted April 23. Kim Deti, a spokesperson for the Wyoming Health Department, said the graph of uptake in her state told the vaccine’s story: a significant climb in the early weeks of its rollout, followed by a plateau that began around the pause. State officials had initially hoped the Johnson & Johnson shot would be a workhorse: a versatile, easy-to-store tool they could stockpile at mass vaccination sites, quickly reaching thousands of people they would not need to track down for a second dose. But after demand dropped, their goals grew more modest. It is being used in a smaller-bore fashion this week at the Fiesta festival in San Antonio, the College World Series in Omaha, Nebraska, a Juneteenth celebration in Johnstown, Pennsylvania, and an aquarium in Long Beach, California. At a food bank in Reno, Nevada, 12 doses of the Johnson & Johnson vaccine were administered Thursday, said Jocelyn Lantrip, director of marketing and communications for the Food Bank of Northern Nevada. Between the small number of doses distributed and the lack of interest in them, public health experts say, the United States missed a critical opportunity to address health disparities with a vaccine that should have been ideal for reaching vulnerable populations. Dr. Chip Riggins, a regional medical director who oversees vaccine events in south central Louisiana, said that few organizers requested the shot anymore, even in a state with one of the lowest vaccination rates in the country. “In the early days of J&J, working with the African American community and the churches, the faith community here, it was a very, very popular option,” Riggins said. “It pains me that it isn’t being accepted like it was before the pause.” Dr. José R. Romero, the Arkansas health secretary, called the shot’s fast decline a “lost opportunity” for reaching the vulnerable in his state. “This is a vaccine that was very well-suited for populations where we have problems getting into,” he said. “We’re now at the point where it’s five people or three people; it doesn’t matter, we’ll open a vial.” Riggins said he had limited success in recent months sending the vaccine to churches, casinos and even gas stations, including one in LaPlace, Louisiana, where organizers offered the shot Thursday. An international crew on a ship was elated to receive their shots last weekend, Riggins said. But not being able to fully protect more people with just a single dose, he added, was hindering the state’s progress. Johnson & Johnson’s decline in the United States has dovetailed with decreasing demand for COVID vaccines overall. Nearly 30 million doses of the Pfizer-BioNTech vaccine are sitting unused, as are about 25 million of Moderna’s. But a total of 135 million people have been fully immunized with those vaccines, 11 times more than with Johnson & Johnson’s. The two-dose vaccines have a higher efficacy rate overall — roughly 95% versus 72% for Johnson & Johnson’s — but studies showed that all three were highly effective at preventing hospitalization and death. Alex Gorsky, Johnson & Johnson’s CEO, said last week that he was still hopeful that the vaccine, which has been used in 26 countries, would help contain the pandemic overseas. The company has promised up to 400 million doses to the African Union. Separately, COVAX, the global vaccine-sharing program, is supposed to receive hundreds of millions of doses. “We still believe that this is going to be a very important tool in the overall armamentarium,” Gorsky said at an event hosted by The Wall Street Journal. But manufacturing problems at a factory in Baltimore run by Emergent BioSolutions, Johnson & Johnson’s subcontractor, have had serious consequences for the vaccine. Because of a major production mishap that resulted in a two-month shutdown in operations, Johnson & Johnson has essentially been forced to sit out the brunt of the pandemic in the United States while Pfizer and Moderna, the other federally authorized vaccine makers, provided almost all the nation’s vaccine stock. Johnson & Johnson has had to throw out the equivalent of 75 million doses, and the regulatory authorities in Canada, South Africa and the European Union also decided to pull back millions more doses made at the Baltimore plant. The company has been able to deliver less than half of the 100 million doses it promised the federal government by the end of this month. Dr. Anne Zink, Alaska’s chief medical officer, said that in her state, Johnson & Johnson’s shot had become a victim of its own timing. By late February, when it was authorized by the Food and Drug Administration, Alaska had figured out how to get two-dose vaccines to remote areas, leaving the one-shot regimen less crucial than she had initially imagined. Dr. Clay Marsh, West Virginia’s COVID-19 czar, said that the pause and Johnson & Johnson’s later authorization — more than two months after Pfizer’s and Moderna’s — deprived it of a “halo effect.” By the time West Virginia had an ample supply of all three vaccines, he said, “people started to get this concept that maybe there’s something better about being immunized with Pfizer and Moderna.” The Johnson & Johnson shot had also suffered from a “social network effect,” said Andrew C. Anderson, a professor of public health at Tulane University who researches vaccine hesitancy. Most Americans who were inoculated in the early months of the vaccine campaign received Moderna and Pfizer shots, and so their friends and family were less likely to deviate and accept a different brand. In Louisiana, hospitals in the New Orleans area have started offering the Johnson & Johnson shot to people on their way out of the emergency room; the thinking is that people will be more likely to accept the vaccine when a doctor who has treated them asks them to take it. And in Arkansas, where only one-third of the population is fully vaccinated, state officials are offering Johnson & Johnson doses to agriculture, manufacturing, wastewater and poultry workers, with gift certificates for hunting and fishing licenses as a reward. “I don’t think that the book on J&J is closed,” said Dr. Joseph Kanter, Louisiana’s top health official. “It’s just not going to be a game changer.” In West Virginia, officials are now hoping to use up some 20,000 doses of the shot at summer fairs and festivals and in parks, Marsh said. And in Oregon, Baden, the state health authority official, said that providers were working to exhaust about 150,000 doses in correctional facilities and higher-throughput sites in Portland. The sharp drop in interest, he said, was “tragic.” Onisis Stefas, chief pharmacy officer at Northwell Health, New York state’s largest health care provider, said he was still working through the system’s original allocation of Johnson & Johnson from March — a sign that demand had shriveled long ago. Doctors’ offices have asked for as few as 10 doses at a time instead of the pack of 50 the vaccine typically comes in. In Michigan, where more than 200,000 Johnson & Johnson doses sit unused, officials are racing to redistribute the vaccine to high-volume sites in hopes of administering them before they expire. “It’s just kind of one after another negative news about the vaccine,” said Dr. Joneigh S. Khaldun, the chief medical executive in the state.

High hopes for Johnson & Johnson’s COVID vaccine have fizzled in the US

The AstraZeneca and Johnson &amp; Johnson vaccines have come under suspicion of causing very rare but serious blood clots in a handful of cases among the millions vaccinated in the drive to bring the Covid-19 pandemic under control. &nbsp; &nbsp;

Questions have persisted for weeks on whether the highly unusual&nbsp;blood&nbsp;clots among those getting the AstraZeneca vaccine were more frequent than in the general population, and what causes them if they were.

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Here is what we know about the two vaccines, which are based on the same technology.&nbsp;

What happened?

The European Medicines Agency last week said unusual blood clots should be listed as a very rare side effect of the AstraZeneca vaccine, while stressing that overall benefits of the shots in preventing Covid-19 outweighed the risks.&nbsp;

The clots occur in veins in the brain, called cerebral venous sinus thrombosis (CVST),&nbsp;as well as the abdomen and arteries.&nbsp;

They are uncommon both for where they appear in the body and because they occur together with low levels of blood platelets, which help the blood to clot.&nbsp;

Paradoxically, this can mean the patient has both haemorrhages as well as blood clots.

There were 222 cases of these atypical thromboses out of 34 million AstraZeneca injections carried out in the European Economic Area (EU, Iceland, Norway, Liechtenstein) and Britain, as of April 4, according to the EMA. And there were 18 deaths, as of March 22.&nbsp;

Most of the cases reported were in women under 60 years of age within two weeks of vaccination.

In the US, where more than 6.8 million single-shot J&amp;J vaccine shots have been administered, health authorities on Tuesday recommended that use of the jab be paused while they investigate six reported cases of CVST that also occurred with low levels of blood platelets. &nbsp;

All those cases involved women between the ages of 18 and 48 and one case was fatal, officials said.

Suspected causes

Both of these vaccines, as well as the Russian Sputnik V jab, are based on a technique known as "viral vector".&nbsp;

The vaccines use a common-cold causing adenovirus, modified so it can't replicate, as a "vector" to shuttle genetic instructions into human cells, telling them to create a protein of the coronavirus.

This trains the immune system to be ready for the live coronavirus

AstraZeneca opted for a chimpanzee adenovirus, J&amp;J for a human adenovirus.&nbsp;

"Whilst a causal link between certain Covid-19 vaccinations, platelet abnormalities, and blood clots has not, so far, been confirmed, the index of suspicion is rising that these rare cases may be triggered by the adenovirus component of the AstraZeneca and J&amp;J vaccines," said Eleanor Riley, an immunology professor at Edinburgh University.&nbsp;

What mechanism?&nbsp;

Although nothing has been proven, Peter Marks of the US Food and Drug Administration said the "probable cause" of the clots could be an unusual reaction to the vaccines.

The FDA has also said that while in normal circumstances an anticoagulant drug called heparin is used to treat these blood clots, in this case administering heparin may be dangerous.

That might be because the disorder resembles a rare reaction to heparin itself, in which the body forms antibodies in response to the thinner, and in turn triggers platelets to form dangerous clots.

A team of German and Austrian scientists made the connection between this previously-known immune response to heparin and the AstraZeneca vaccine in March.

And the EMA said this was "one plausible explanation", calling for more research.&nbsp;

What have the regulators said?

The CDC is recommending pausing using J&amp;J's single-dose vaccine "out of an abundance of caution" to ensure that the health care providers are aware of potential side effects and can plan for "proper recognition and management."

Britain's Medicines and Healthcare products Regulatory Agency, meanwhile, made its recommendation for an alternative vaccine to AstraZeneca's to be used for people under 30 after reviewing 79 cases of rare&nbsp;clotting coupled with low platelets, with 19 fatalities - 13 women and six men. Eleven of the deaths were of people under the age of 50 and three were under the age of 30.

Balancing risk

The European agency has said no specific risk factors for this type of reaction have been confirmed for the AstraZeneca vaccine, but different countries have opted to restrict access to the jab by age.&nbsp;

The reasoning is that the older people get, the more they risk developing a serious form of Covid, and the more it is in their interest to be vaccinated, despite potential side effects.&nbsp;

For example, Britain has said it will not administer AstraZeneca to the under 30s, while France is not using it on the under 55s. &nbsp;&nbsp;

In the US, health authorities said the suspension of the J&amp;J vaccine was "out of an abundance of caution".&nbsp;

People who have had the shot within the past three weeks were asked to report to their doctors if they experience severe headaches, abdominal pain, leg pain, or shortness of breath.

Ian Douglas, Professor of Pharmacoepidemiology at London School of Hygiene &amp; Tropical Medicine, said it was important to underscore how rare these events appear to be.&nbsp;

"To put this into perspective, it's similar to the chance of being struck by lightning in any given year in the UK," he told the Science Media Centre in response to the US announcement.

"On the other hand, the risks from Covid-19 are substantial." &nbsp;

The AstraZeneca and Johnson & Johnson vaccines have come under suspicion of causing very rare but serious blood clots in a handful of cases among the millions vaccinated in the drive to bring the Covid-19 pandemic under control.

The AstraZeneca and Johnson & Johnson vaccines have come under suspicion of causing very rare but serious blood clots in a handful of cases among the millions vaccinated in the drive to bring the Covid-19 pandemic under control. Questions have persisted for weeks on whether the highly unusual blood clots among those getting the AstraZeneca vaccine were more frequent than in the general population, and what causes them if they were. Here is what we know about the two vaccines, which are based on the same technology. What happened? The European Medicines Agency last week said unusual blood clots should be listed as a very rare side effect of the AstraZeneca vaccine, while stressing that overall benefits of the shots in preventing Covid-19 outweighed the risks. The clots occur in veins in the brain, called cerebral venous sinus thrombosis (CVST), as well as the abdomen and arteries. They are uncommon both for where they appear in the body and because they occur together with low levels of blood platelets, which help the blood to clot. Paradoxically, this can mean the patient has both haemorrhages as well as blood clots. There were 222 cases of these atypical thromboses out of 34 million AstraZeneca injections carried out in the European Economic Area (EU, Iceland, Norway, Liechtenstein) and Britain, as of April 4, according to the EMA. And there were 18 deaths, as of March 22. Most of the cases reported were in women under 60 years of age within two weeks of vaccination. In the US, where more than 6.8 million single-shot J&J vaccine shots have been administered, health authorities on Tuesday recommended that use of the jab be paused while they investigate six reported cases of CVST that also occurred with low levels of blood platelets. All those cases involved women between the ages of 18 and 48 and one case was fatal, officials said. Suspected causes Both of these vaccines, as well as the Russian Sputnik V jab, are based on a technique known as "viral vector". The vaccines use a common-cold causing adenovirus, modified so it can't replicate, as a "vector" to shuttle genetic instructions into human cells, telling them to create a protein of the coronavirus. This trains the immune system to be ready for the live coronavirus AstraZeneca opted for a chimpanzee adenovirus, J&J for a human adenovirus. "Whilst a causal link between certain Covid-19 vaccinations, platelet abnormalities, and blood clots has not, so far, been confirmed, the index of suspicion is rising that these rare cases may be triggered by the adenovirus component of the AstraZeneca and J&J vaccines," said Eleanor Riley, an immunology professor at Edinburgh University. What mechanism? Although nothing has been proven, Peter Marks of the US Food and Drug Administration said the "probable cause" of the clots could be an unusual reaction to the vaccines. The FDA has also said that while in normal circumstances an anticoagulant drug called heparin is used to treat these blood clots, in this case administering heparin may be dangerous. That might be because the disorder resembles a rare reaction to heparin itself, in which the body forms antibodies in response to the thinner, and in turn triggers platelets to form dangerous clots. A team of German and Austrian scientists made the connection between this previously-known immune response to heparin and the AstraZeneca vaccine in March. And the EMA said this was "one plausible explanation", calling for more research. What have the regulators said? The CDC is recommending pausing using J&J's single-dose vaccine "out of an abundance of caution" to ensure that the health care providers are aware of potential side effects and can plan for "proper recognition and management." Britain's Medicines and Healthcare products Regulatory Agency, meanwhile, made its recommendation for an alternative vaccine to AstraZeneca's to be used for people under 30 after reviewing 79 cases of rare clotting coupled with low platelets, with 19 fatalities - 13 women and six men. Eleven of the deaths were of people under the age of 50 and three were under the age of 30. Balancing risk The European agency has said no specific risk factors for this type of reaction have been confirmed for the AstraZeneca vaccine, but different countries have opted to restrict access to the jab by age. The reasoning is that the older people get, the more they risk developing a serious form of Covid, and the more it is in their interest to be vaccinated, despite potential side effects. For example, Britain has said it will not administer AstraZeneca to the under 30s, while France is not using it on the under 55s. In the US, health authorities said the suspension of the J&J vaccine was "out of an abundance of caution". People who have had the shot within the past three weeks were asked to report to their doctors if they experience severe headaches, abdominal pain, leg pain, or shortness of breath. Ian Douglas, Professor of Pharmacoepidemiology at London School of Hygiene & Tropical Medicine, said it was important to underscore how rare these events appear to be. "To put this into perspective, it's similar to the chance of being struck by lightning in any given year in the UK," he told the Science Media Centre in response to the US announcement. "On the other hand, the risks from Covid-19 are substantial."

Blood clots are latest curse of coronavirus vaccines. All you need to know

Canada’s drug regulator has approved Johnson &amp; Johnson’s single-dose COVID-19 vaccine. This is the fourth such vaccine to be given the green light -- Health Canada approved the Pfizer-BioNTech and Moderna Inc vaccines in December, and AstraZeneca’s vaccine in February.

It is the first single-dose Covid-19 vaccine to be authorised in the country, and has been cleared for use by people over 18 years of age.&nbsp;

The official announcement will be made later on Friday.&nbsp;

The vaccine is administered in a single dose and can be stored in normal fridges while the Pfizer-BioNTech and Moderna shots must be kept in freezers.

Ottawa has ordered up to 38 million doses, which can be stored at refrigerated temperatures from two to eight degrees Celsius (35-46 Fahrenheit), making distribution easier than some others.

So far, 4.2 per cent of the Canadian population has received at least one dose of a coronavirus vaccine, according to volunteer-run tracking site COVID-19 Tracker Canada. In the United States, more than 16 per cent have received at least one dose.

Health officials are expected to announce in the coming weeks a decision on Novovax's vaccine candidate -- the only other one to have submitted an application for approval to date.

As of Friday, Canada has reported more than 878,000 cases of the coronavirus and over 22,000 fatalities.

Canada’s drug regulator has approved Johnson & Johnson’s single-dose COVID-19 vaccine. This is the fourth such vaccine to be given the green light -- Health Canada approved the Pfizer-BioNTech and Moderna Inc vaccines in December, and AstraZeneca’s vaccine in February.

Canada’s drug regulator has approved Johnson & Johnson’s single-dose COVID-19 vaccine. This is the fourth such vaccine to be given the green light -- Health Canada approved the Pfizer-BioNTech and Moderna Inc vaccines in December, and AstraZeneca’s vaccine in February. It is the first single-dose Covid-19 vaccine to be authorised in the country, and has been cleared for use by people over 18 years of age. The official announcement will be made later on Friday. The vaccine is administered in a single dose and can be stored in normal fridges while the Pfizer-BioNTech and Moderna shots must be kept in freezers. Ottawa has ordered up to 38 million doses, which can be stored at refrigerated temperatures from two to eight degrees Celsius (35-46 Fahrenheit), making distribution easier than some others. So far, 4.2 per cent of the Canadian population has received at least one dose of a coronavirus vaccine, according to volunteer-run tracking site COVID-19 Tracker Canada. In the United States, more than 16 per cent have received at least one dose. Health officials are expected to announce in the coming weeks a decision on Novovax's vaccine candidate -- the only other one to have submitted an application for approval to date. As of Friday, Canada has reported more than 878,000 cases of the coronavirus and over 22,000 fatalities.

Canada approves Johnson & Johnson Covid vaccine