AstraZeneca COVID-19 vaccine safety and efficacy – no reason to refuse it

  • 1
  • 4

I have been noting with alarm that the safety and effectiveness of the AstraZeneca COVID-19 vaccine – it’s concerning people, and sometimes governments, are refusing the vaccine. This is wrong.

My girlfriend, an ER physician who is literally exhausted from saving lives during this pandemic, wrote this recently:

So many lives have been lost to COVID-19. Please vaccinate.

I may write picky things about these vaccines, just to follow the science, but in the end, I don’t care which COVID-19 vaccine I received and you shouldn’t either. The AstraZeneca vaccine is demonstrably safe and demonstrably effective.

I have made an effort to push the facts and debunk the myths about all of the COVID-19 vaccines. I think the AstraZeneca one needs

The AstraZeneca COVID-19 vaccine

The AstraZeneca COVID-19 vaccine is very different than the Pfizer and Moderna mRNA vaccines but is very similar to the JNJ vaccine. The vaccine still induces an adaptive immune memory response to the S-protein of the SARS-CoV-2 virus which causes COVID-19.

The AstraZeneca COVID-19 vaccine utilizes a recombined adenovirus vector, chimpanzee ChAdOx1, which causes the production of the S-subunit of the SARS-CoV-2 virus which induces an immune response to that S-subunit. Basically, the adenovirus vector “carries” the genes for the S-subunit to the cell which will reproduce the protein, then inducing the immune response.

Adenovirus-based vaccines have been investigated for several decades. In fact, JNJ has received approval for an Ebola adenovirus vaccine in July 2020, so the technology did not just appear suddenly to be used to fight COVID-19-19. However, like the mRNA vaccines, these adenovirus vaccines, also used by JNJ, can be quickly developed to deliver the most important antigen on the SARS-CoV-2 virus, which is the S-protein.

There is an advantage to adenovirus-based vaccines – they are much less fragile than mRNA vaccines because they are based on DNA which is more rugged than RNA.

Once the AstraZeneca vaccine is injected into the arm, the adenoviruses enter cells and moves to the nucleus, where the cell’s genes (DNA) are located.

The adenovirus then injects its DNA into the nucleus. The adenovirus is engineered so it can’t make copies of itself, but the gene for the coronavirus spike protein can be read by the cell and copied into a molecule called messenger RNA, or mRNA.

At this point, it is similar to the mRNA vaccines.

Normally, during the process called transcription, RNA polymerase makes a copy of a gene from its DNA to a corresponding mRNA fragment whenever required by the cell. In other words, the mRNA sequences in the cell usually correspond directly to the DNA sequences in our genes. These mRNA sequences “carry” that genetic message to a ribosome for translation, where tRNA triplets, which code for one amino acid, attach to the appropriate mRNA triplet, adding one amino acid to the protein chain. 

As in DNA, genetic information in mRNA is contained in the sequence of nucleotides, which are arranged into codons consisting of three ribonucleotides each. Each codon codes for a specific amino acid, except the stop codons, which terminate protein synthesis.

Like with mRNA vaccines, the adenovirus does not change the genetic code of any of the 50 trillion cells that are in a human. All that happens is that the adenovirus injects DNA that is coded for the S-protein and the cell produces mRNA from that DNA that then causes the ribosomes to produce the S-protein.

Those S-proteins migrate to the surface of the cell which is then recognized by the immune system as foreign invaders. The immune system then remembers those antigens – when the actual SARS-CoV-2 virus attacks, the immune system is ready to attack.

The AstraZeneca COVID-19 vaccine also has one additional advantage over the mRNA vaccines – the adenovirus itself provokes the immune system to activate immune cells that are nearby. This leads to the immune system reacting more strongly to the spike proteins.

AstraZeneca COVID-19 vaccine safety and efficacy

I’m going to focus on three topics regarding the AstraZeneca vaccine which seemed to have gotten a lot of press recently.:

  1. Safety, especially with blood clots.
  2. Clinical trial design.
  3. Overall effectiveness.

Blood clots

I have dealt with this issue in a previous article, and one can only conclude that the vaccine is probably not linked to thrombi. But let’s dive into the weeds for a moment.

According to AstraZeneca, 15 reports of deep vein thrombosis and 22 reports of pulmonary embolism, both caused by blood clots, in patients who have received their COVID-19 vaccine. These observations are out of 17 million patients who received the vaccine in the UK and Europe.

Despite that, several countries in the EU temporarily suspended vaccinations, which lead to a critical slowdown in the vaccination effort in several countries, despite a recent surge.

To put this into some perspective, let’s do the math:

  • For deep vein thrombosis, that means the observed risk after the AstraZeneca COVID-19 vaccines is 0.88 per 1 million vaccinated individuals.
  • For pulmonary embolism, the observed risk would be around 1.29 per 1 million vaccinated individuals.
  • The overall risk of these two types of blood clot events is about 1 in 1000 in the general population, substantially higher than the “risk” after the AstraZeneca COVID-19 vaccine. I’m not saying that getting the vaccine prevents blood clots, but a bad use of statistics would lead one to such a conclusion.

So far, the large, well-controlled clinical trials for the AstraZeneca and JNJ (which is also based on adenovirus vector technology) have not shown any increased risk for blood clots.

Yes, the SARS-CoV-2 virus seems to cause thrombi in many patients, which might lead one to think there is some biological plausibility to the blood clot issue. However, no live virus is used in the Pfizer, Moderna, JNJ, and AstraZeneca vaccines. All four of these vaccines induce the production of one small part of the virus, the spike protein, for a limited time. A real infection by SARS-CoV-2 will have billions of viruses all replicating and causing havoc to the body.

Finally, we don’t have any information on these patients that experienced thrombi post-vaccination – are there confounders that might cause a higher risk for blood clots, such as smoking, obesity, diabetes, and other comorbidities for thrombus? Those may be more important to the risk of clots than the AstraZeneca vaccine, and that’s why we investigate each claim to determine if there is a potential link.

It seems clear that the thrombus is not a safety issue for the AstraZeneca COVID-19 vaccine, but good scientists will continue to monitor the situation.

Clinical trial design

There has been some criticism of AstraZeneca’s clinical trial design, including a recent rebuke from the National Institute of Allergy and Infectious Diseases (NIAID), run by Dr. Anthony Fauci. They stated that:

…expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data. We urge the company to work with the DSMB to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible.

Let’s parse this very clearly. They are not saying that AstraZeneca did anything improper. They did not say that the AstraZeneca COVID-19 vaccine safety profile was concerning. They did not say that the vaccine was ineffective.

NIAID is basically saying that AstraZeneca may have cherry-picked older results while not including newer ones which may provide an inaccurate view of the effectiveness of the vaccine. AstraZeneca put out press releases that claimed that it was 79% effective, while more recent data reviewed by the NIH put the vaccine efficacy between 69% and 74%.


This, of course, leads to the discussion of the overall effectiveness of the AstraZeneca vaccine. As I discussed recently, one should not compare the effectiveness of one vaccine to another just on a single number.

It is difficult to compare one clinical trial to another to determine whether one vaccine is more effective than another. The Moderna and Pfizer COVID-19 vaccines were in clinical trials during the earliest part of the pandemic, whereas the JNJ vaccine underwent clinical trials during the later part of the pandemic where there were more virulent variants of the disease out in the world.

Overall, the four vaccines from Moderna, Pfizer, AstraZeneca, and JNJ do two important things:

  • They prevent death from COVID-19.
  • They prevent hospitalization from COVID-19.

And that’s why we vaccinate.

astrazeneca COVID-19 vaccine safety
Photo by David Vives on Unsplash

Shouting from the rooftops

Let me repeat the quote I wrote in the introduction:

So many lives have been lost to COVID-19. Please vaccinate.

This isn’t the time to pick and choose which vaccine to get. All four are approximately equal. And the safety and effectiveness profiles of the AstraZeneca COVID-19 vaccine mean that if it is available, get it. Period. End of rant.


Just for brevity about these safety and effectiveness issues, I call this the AstraZeneca COVID-19 vaccine. The official name is ChAdOx1, and it was developed in conjunction with Oxford University Jenner Institute, a leading vaccine research institute in the UK.

Because AstraZeneca is responsible for testing, clinical trials, manufacturing, marketing, and regulatory approvals, it is unofficially known as the AstraZeneca vaccine. This should not suggest that the Jenner Institute had only a minimal role in this process, because without them AstraZeneca may not have a vaccine.

Please help me out by sharing this article. Also, please comment below, whether it's positive or negative. Of course, if you find spelling errors, tell me!

There are two ways you can help support this blog. First, you can use Patreon by clicking on the link below. It allows you to set up a monthly donation, which will go a long way to supporting the Skeptical Raptor
Become a Patron!

Finally, you can also purchase anything on Amazon, and a small portion of each purchase goes to this website. Just click below, and shop for everything.

The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!