There are several COVID-19 vaccines out right now, including one from AstraZeneca. Although it has been approved for use in other countries, it has not yet been approved by the Food and Drug Administration (FDA).
Knowing more about the AstraZeneca vaccine can help you make informed decisions about which vaccine to get if it does get approved for use in the United States.
The AstraZeneca COVID-19 vaccine, now called Vaxzevria, is a viral vector vaccine, just like the vaccine from Johnson & Johnson.
The vaccine uses a chimpanzee adenovirus to carry spike proteins from the coronavirus into your body to create an immune response. It can be produced on a large scale and inexpensively, which is crucial during a pandemic. It can also be kept in a regular refrigerator, unlike the vaccines from Pfizer and Moderna.
Despite initial pauses about its safety with blood clots, it has been deemed safe by the European Medicines Agency (EMA) and is still recommended by the World Health Organization (WHO).
Right now, no coronavirus vaccine is fully approved by the FDA. The vaccines in use have been granted emergency use authorization. This means that the known and potential benefits of the vaccine outweigh the known and potential risks.
The AstraZeneca COVID-19 vaccine is not yet approved in the United States because the FDA has asked AstraZeneca to show results from a large-scale trial.
The FDA found that in initial trials, some participants mistakenly got half doses of the vaccine. They also
In March 2021, several European countries paused the use of the AstraZeneca COVID-19 vaccine after several reports of blood clots. The clots that are linked to this vaccine have very specific characteristics:
- They occur in unusual areas of the body, like the abdomen or brain.
- People affected also have low platelet levels.
It was found that people with these blood clots showed some symptoms similar to a condition called heparin-induced thrombocytopenia (HIT). HIT is usually a rare side effect seen in people who have used the anticoagulant medication heparin, though these people had never taken the drug.
At this point, researchers aren’t sure what part of the vaccine is causing an immune response against a platelet factor involved in this reaction. Because a similar response has been seen in the J&J vaccine, which also uses an adenovirus, and not seen in the vaccines that use mRNA, this may be an issue with vaccines using adenovirus.
Although this is a serious adverse effect, it’s also important to look at the context.
Over 20 million doses of the AstraZeneca vaccine have been given in the United Kingdom. The risk of a serious blood clot is about 1 in 250,000 people or 4 in a million. COVID-19 carries a much higher risk of blood clots: 7.8 percent of people who have had COVID-19 also have pulmonary embolism and 11.2 percent experience deep vein thrombosis.
The AstraZeneca vaccine uses a common cold-causing chimpanzee adenovirus, or a vector, to transport some of the coronavirus DNA to your cells. Your cells then take that DNA and convert it into the spike protein of the virus, which is what the virus uses to enter cells and cause an infection.
Your cells mount an immune response — but the amount of actual virus is so small, you don’t actually get an infection with the disease.
The vaccine is
While Moderna and Pfizer are based on mRNA, the AstraZeneca vaccine is a viral vector vaccine. This means it uses a different mechanism to induce an immune response. The second dose is also given at a longer interval, instead of the 3- to 4-week suggested interval with the others.
Both the AstraZeneca and Johnson & Johnson vaccines are viral vector vaccines. These kinds of vaccines use a modified, harmless version of a virus as a vector — a carrier — to the cells in the body. Your body then acts accordingly and mounts an immune response to the virus.
The viral vector in these two vaccines is an adenovirus. This vector carries the information that is needed for the body to produce an immune response to SARS-CoV-2, the virus that causes COVID-19.
Studies of the efficacy of this vaccine have been wide-ranging. A pooled analysis of four large studies found that in groups that received two standard doses of the AstraZeneca vaccine, the overall efficacy was
Several months later, AstraZeneca announced it was 76 percent effective at preventing symptomatic disease. In a group that received a lower dose initially, the surprising result was a finding of
The AstraZeneca COVID-19 vaccine offers another option for vaccination against COVID-19 in some countries. The AstraZeneca COVID-19 vaccine is not approved for use in the United States.
Although more research is being done regarding blood clots, it seems this is a very small percentage of reactions. If the FDA grants emergency use authorization for the AstraZeneca COVID-19 vaccine, it could be helpful in getting more people vaccinated, especially because it is cheaper and able to be kept at lower temperatures.