getting the AstraZeneca COVID-19 VaccineShare on Pinterest
Phynart Studio/Getty Images

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) in the United States.

Knowing more about the AstraZeneca vaccine can help you make an informed decision 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 Johnson & Johnson vaccine.

It uses a chimpanzee adenovirus to carry spike proteins from the coronavirus into your body to create an immune response. It can also be kept in a regular refrigerator, unlike the Pfizer and Moderna vaccines.

Although mRNA vaccines like Pfizer and Moderna are actually easier to produce more quickly, the cold chain storage required to bring them to lower-income countries does not exist. This is why the AstraZeneca and Johnson & Johnson vaccines are incredibly important to global health.

Despite initial pauses about its safety regarding blood clots, the AstraZeneca vaccine has been deemed safe by the European Medicines Agency (EMA) and is still recommended by the World Health Organization (WHO).

The Pfizer vaccine is fully approved by the FDA for use in people ages 16 and above. The other vaccines in use have been granted emergency use authorization, which means 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vaccine is not yet approved in the United States because the one large-scale trial of the vaccine conducted so far used outdated data.

The FDA found that in initial trials, some participants mistakenly got half doses of the vaccine. It also found that the trial did not include enough people over 55 years old. It asked the company to do a larger trial in order to get clearer data.

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 less common 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 thrombotic thrombocytopenia (HITT).

HITT is a rare side effect sometimes seen in people who have used heparin, an anticoagulant medication. But the people vaccinated had never taken this drug. Researchers refer to this new condition as VITT (vaccine-induced thrombotic thrombocytopenia).

At this point, researchers are not sure which part of the vaccine is causing an immune response against a platelet factor involved in this reaction.

A similar response has been seen in the Johnson & Johnson vaccine, which also uses an adenovirus. But this response has not been seen in the vaccines that use mRNA, so it may be an issue with vaccines using an 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 1 million.

COVID-19 carries a much higher risk of blood clots: 7.8 percent of people who have had COVID-19 also had a 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 spike protein in DNA to your cells. Your cells then take that DNA and convert it into the spike protein of the virus. This is what the virus uses to enter cells and cause an infection.

Your cells set up an immune response. Instead of making the virus, they create its outer shell. This is because actual coronaviruses are made up of single-strand RNA, not the DNA in the vaccine. So you do not actually get an infection with the disease.

The vaccine is given in two doses, with a suggested gap of 8 to 12 weeks between doses.

While Moderna and Pfizer are based on mRNA, the AstraZeneca vaccine is a viral vector vaccine. This means it uses a different mechanism to create 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 your 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 your 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 70.4 percent.

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 90 percent efficacy. The reasons for this are unclear, and more research needs to be done to provide a better understanding.

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 yet.

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’s cheaper and can be kept at lower temperatures.