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The facts about AstraZeneca's COVID-19 vaccine

Louisa Wright | Kathrin Wesolowski
March 18, 2021

The AstraZeneca vaccine was praised for its cost-effectiveness and its easy-to-store advantages. But recent cases of blood clots linked to the vaccine have led to doubts about its safety.

A vial of AstraZeneca vaccine
AstraZeneca's jab was less effective in trials against B.1.351, but it is still recommendedImage: Valentina Petrova/AP Photo/picture alliance

How effective is the AstraZeneca vaccine?

The company has had to revise down the vaccine's efficacy. In a release on its website (March 25), AstraZeneca said the vaccine is 76% effective at preventing COVID-19 instead of an earlier figure of 79%. However, in the age group 65 and over the value is higher at 85%. According to the company, the vaccine is 100% effective against serious illnesses caused by COVID-19.

This comes as Anthony Fauci, the director of the US Institute of Allergy and Infectious Diseases (NIAD), voiced doubts about the vaccine's effectiveness. According to apress release, the institute said it was concerned about reports that "AstraZeneca may have included outdated information" from a US trial that may have yielded "an incomplete view of the efficacy data." The company has announced it will release new data. The vaccine has not yet been approved in the United States.

Earlier results from late-stage studies in the UK, Brazil and South Africa have shown the vaccine to be 82% effective when a second dose is given 12 weeks or more after the first dose. The vaccine has also been found to reduce the duration of shedding and viral load, which could slow down transmission of the virus. 

A study of the AstraZeneca vaccine's potency against the B.1.1.7 variant, first reported in the UK, found that the efficacy was similar to its efficacy against the original virus. 

In terms of hospital admissions, there is good news regarding the effect the vaccinations are having. A study by the University of Edinburghshowed that four weeks after the first jab with AstraZeneca, the risk of those vaccinated being hospitalized fell by 94%. The study also found that an injection with the BioNTech vaccine reduces that risk by 85%.

German researchers discover thrombosis trigger

Researchers at the Greifswald teaching hospital in northern Germany said recently they had discovered the cause of the unusual blood clot problems found in some recipients of the AstraZeneca coronavirus vaccine.

The discovery means that targeted treatment can be developed to avoid serious problems. Researchers have emphasized that treatment would only be possible in patients after blood clots appear, rather than as a preventative treatment to stop a thromboembolic event. 

What is the health authorities' guidance on the use of the AstraZeneca vaccine?

The European Medicines Agency has said the AstraZeneca vaccine is safe for use. It will conduct additional studies into any possible links between the vaccine and blood clots. "Its benefits continue to be far greater than its risks," the EMA said at a press conference.

The World Health Organization said in a statement that, at this time, it also considers the benefits of the AstraZeneca vaccine to outweigh its risks and recommends that vaccinations continue. It noted that vaccination against COVID-19 will not reduce illness or deaths from other causes and thromboembolic events are known to occur frequently in general.

Why was the use of the vaccine suspended?

Germany, Italy and France had stopped using the AstraZeneca vaccine as a precautionary measure. Iceland, Ireland and Bulgaria had also suspended the use

Germany resumed administering the jab on March 19. The vaccine, however, will come with new advice on potential side effects. 

Norway and Sweden will keep the AstraZeneca vaccine suspended as their public health bodies assess the situation.  Meanwhile, public confidence in the vaccine is on the wane in a number of European countries. A new survey shows that a majority of people in leading EU member countries feel that the vaccine is unsafe.

Estonia, Lithuania, Luxembourg, Latvia and Romania suspended the use of AstraZeneca vaccine batch ABV5300 following Austria's decision to suspend the batch after one person died from multiple thrombosis 10 days after vaccination and another was hospitalized with pulmonary embolism after getting the shot.

Batch ABV5300 was delivered to 17 European Union countries and comprises 1 million doses of the vaccine.

In early March, the Danish Health Ministry announced that it would stop using the AstraZeneca vaccine for the time being. This comes after "reports of severe blood clots in people vaccinated with the AstraZeneca COVID-19 vaccine," the ministry said in a statement. "We need clarification before we can continue to use the vaccine from AstraZeneca," said Soren Brostrom, Director General of the Danish Health Authority, which advises and works with the Health Ministry.

The backdrop to the investigation is an as yet unexplained death in Denmark in connection with a vaccination. "At the moment it cannot be ruled out whether there is a connection between the vaccine and the blood clots," said the Health Ministry.

Norway followed suit as a result of the case in Denmark and put the AstraZeneca vaccine on hold. In a press statement, Geir Bukholm, Director of the Division of Infection Control and Environmental Health at the Norwegian Institute of Public Health NIPH), said this was a precautionary measure. "We will wait for information to see if there is an association between the vaccine and this case."

Sara Viksmoen Watle, a senior NIPH physician told DW that her institute was "now carefully reviewing all reported side effects after the AstraZeneca vaccine and other coronavirus vaccines. In addition, we will investigate whether there are cases of blood clots after vaccination that have not been reported, and ask healthcare professionals who suspect such an association to report this as soon as possible. We are also looking at whether we find indications that there is an increase of certain conditions in the health registries that could be side effects."

The EMA has said there is currently no known case of a causal link of a death caused by a coronavirus vaccination. You can read more about that in our fact check on vaccines and deaths.

How effective is the AstraZeneca vaccine against the South African variant of COVID-19?

A small trial with 2,000 people in South Africa found that the AstraZeneca vaccine provided "minimal protection" against mild and moderate COVID-19 disease from the B.1.351 coronavirus variant, first identified in South Africa. This variant is causing the majority of infections within the country. 

None of the people in the trial died, became severely ill or had to be hospitalized. Efficacy against severe COVID-19 arising from the B.1.351 variant was not assessed in the study because the participants were at lower risk, researchers at the University of the Witwatersrand in Johannesburg said in their analysis. The study has not yet been peer-reviewed. 

The World Health Organization has recommended the use of the AstraZeneca vaccine even if variants are present in a country, according to interim recommendations published on February 10. 

"Countries should conduct a benefit-risk assessment according to the local epidemiological situation including the extent of circulating virus variants," the interim recommendations state. 

The WHO's recommendations state that indirect evidence is compatible with protection against severe COVID-19, and ongoing clinical trials and evaluations would be needed to demonstrate this. 

Vaccine setback

AstraZeneca said it believes its vaccine could protect against severe disease, according to the Financial Times newspaper

"[The] neutralizing antibody activity is equivalent to that of other COVID-19 vaccines that have demonstrated activity against more severe disease, particularly when the dosing interval is optimized to 8-12 weeks," AstraZeneca reported.

The AstraZeneca vaccine will still provide some protection against the B.1.351 variant because the antibodies created after vaccination will recognize parts of the virus variant and block them, Sarah Pitt, a  principal lecturer at the University of Brighton and fellow at the UK-based Institute of Biomedical Science, told DW. "It is not that it doesn't work at all, it's just not quite as good," Pitt said. 

The variants that a person encounters, and how much immunity a person builds up, can affect how well the vaccine protects them, Pei-Yong Shi, a professor of microbiology at the University of Texas Medical Branch, told DW. Being vaccinated with an approved vaccine will help protect people from developing severe COVID-19, he said. 

"We have a protective defense after vaccination," Shi said. "Maybe you will get a very minor disease, but it's way better than not being vaccinated." 

Why do viruses mutate?

Why isn't the AstraZeneca vaccine as effective against the South African variant?  

The B.1.351 variant (also known as 501Y.V2) has mutations in the spike protein, which is the part of the virus that connects to human cells and enables it to infect them. The mutation scientists are concerned about is called E484K.  

The COVID-19 vaccines that have been approved for use make the body produce antibodies against the spike protein of the original strain of the coronavirus. But now the antibodies are fighting viruses whose spike proteins they do not fully recognize. 

"The shape of the virus has slightly changed, but the response that you're making is based on the original one," Pitt said. 

This means that no antibodies attach to the mutated part of the spike protein, and the virus can still attach itself to a human cell. But the antibodies will block the parts of the virus that it does recognize, so it still provides some protection. 

The antibody level needed to fend off the coronavirus has not been defined yet, Shi said: "That's very important to emphasize." 

study of the Moderna vaccine found that it was slightly less effective against the B.1.351 variant, but the neutralizing levels were still above those expected to be protective. 

A study of the BioNTech-Pfizer vaccine also found that the jab was slightly less effective against the B.1.351 variant. "This is sort of expected," said Shi, who is also one of the study’s authors. "Already it has been well-documented [the E484K mutation] is going to reduce the activity of a lot of monoclonal antibodies." 

What is AstraZeneca doing to address the SA variant?

The head of the Oxford research group, Sarah Gilbert, told the BBC that the vaccine should still protect against severe disease. But at the same time, she said developers are working on a modified vaccine to combat the South African variant. This would likely be ready in autumn, she said.

Should you take the AstraZeneca vaccine if it's offered to you?  

The WHO has recommended the use of the AstraZeneca vaccine for everyone aged 18 and over, even if there are coronavirus variants present, according to interim recommendations. 

The WHO also made recommendations for people with comorbidities that increase the risk of severe COVID-19, people living with HIV and autoimmune conditions, and people who are pregnant.

People who have already had COVID-19 can be vaccinated, according to the WHO, but they may want to delay their own shots for up to six months from the period when they were infected to allow others who need urgent protection to be inoculated. 

People with a history of severe allergic reaction to any ingredient of the vaccine should not take it. 

Even if you get one of the virus variants that was first found in South Africa (known as B.1.351 or 501Y.V2), the UK (B1.1.1.7) or Brazil (P.1), the AstraZeneca vaccine will give you some protection. This is because all of these are variants of the original coronavirus strain that the vaccine was designed to fight. It won’t be able to recognize the parts that have mutated, but it will be able to recognize the rest. 

A COVID-19 vaccination triggers the immune response inside the body, Shi said, "and those responses are protective." 

Both Shi and Pitt emphasized that the vaccine is not the only answer to the pandemic. People need to continue to follow COVID-19 regulations like social distancing, wearing masks and washing their hands regularly. 

Coronavirus vaccines: Can we stay ahead of the variants?

Is the AstraZeneca vaccine safe for use in all ages? 

The World Health Organization has recommended the use of the AstraZeneca vaccine for people aged 18 and over, including people who are 65 and older. 

"Taking the totality of available evidence into account, WHO recommends the vaccine for use in persons aged 65 years and older," the WHO wrote in its interim recommendations for the AstraZeneca vaccine

The European Medicines Agency has also reported the AstraZeneca vaccine can be used to prevent the disease in people aged 18 and older.  

According to the EMA, so far there aren’t enough results in older people to show how well the vaccine will work for them, but that "protection is expected, given that an immune response is seen in this age group and based on experience with other vaccines." 

AstraZeneca said its COVID-19 vaccine has already been granted conditional marketing authorization or emergency use in more than 50 countries, including countries in the EU, a number of Latin American countries, India, Morocco and the UK.

Germany's vaccine commission, STIKO, has advised that AstraZeneca only be given to people aged 64 and under. The commission cited a lack of data regarding the vaccine's effectiveness for older people.  

Most of the participants in AstraZeneca’s studies were between 18 and 55 years old. AstraZeneca said in the write-up of their results that "vaccine efficacy in older age groups could not be assessed."

Who makes the AstraZeneca vaccine?

The vaccine is being developed and produced by a team from Oxford University and the British-Swedish pharmaceutical company AstraZeneca. The research team includes scientists from the Jenner Institute and the Oxford Vaccine Group.

What kind of vaccine is AstraZeneca and how does it work?

AstraZeneca's vaccine is not an mRNA vaccine like Moderna’s and BioNTech-Pfizer’s, but a vector virus vaccine. It uses a harmless cold virus common to chimpanzees as a transport mechanism. The vaccine transports the surface protein of SARS-CoV-2 to human cells, where it triggers an immune response against the coronavirus.

How to get the COVID-19 vaccine to the world

Why is the AstraZeneca vaccine appealing?

Unlike the BioNTech-Pfizer and Moderna vaccines, AstraZeneca's does not have to be stored at ultra-low temperatures. The vaccine can be stored, transported and handled at normal refrigeration temperatures (2-8 degrees Celsius/36-46 degrees Fahrenheit) for at least six months.

BioNTech-Pfizer has had to designed special temperature-controlled thermal shippers that use dry ice to maintain the recommended storage temperature conditions of -70 degrees Celsius (-94 F) for up to 10 days unopened.

According toAstraZeneca, the vaccine's simple supply chain and no-profit pledge will make it more affordable, but the exact price of a dose of the AstraZeneca vaccine is not clear.

AstraZeneca and BioNTech-Pfizer have both made agreements with COVAX, a global initiative that aims to distribute low-cost vaccines to low- and middle-income countries. 

In a tweet that has since been deleted, Belgian State Secretary Eva De Bleeker published the purported EU prices per dose: €15 ($18) for Moderna, €12 for BioNTech-Pfizer and €1.78 for AstraZeneca.

This article was updated on March 26 to reflect revisions to the vaccine's efficacy.

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