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AstraZeneca COVID-19 vaccine shows 70% effectiveness in phase 3

AstraZeneca has announced that its COVID-19 vaccine has exhibited over 70% average effectiveness in phase 3 clinical trials in Brazil and the United Kingdom. The vaccine was initially developed by the University of Oxford, but AstraZeneca will manufacture and distribute the vaccine worldwide.

The AstraZeneca COVID-19 vaccine is the third vaccine over the past few days that has shown extremely high effectiveness following the ones announced by Pfizer and Moderna. However, the AstraZeneca/Oxford vaccine is substantially different in pharmacology and distribution than the other two. 

What is the AstraZeneca COVID-19 vaccine?

As opposed to the Pfizer and Moderna vaccines, which utilize mRNA vaccine technology, the AstraZeneca vaccine employs more traditional vaccine technology.

According to AstraZeneca:

It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.

The AstraZeneca vaccine utilizes a non-replicating viral vector, a chemically weakened virus to transport pieces of the pathogen in order to stimulate an immune response. which makes it appear like the SARS-CoV-2 virus enters the body but without causing an infection. The immune system will “remember” the coronavirus S-protein (or spike protein) giving it a head start to attack a real COVID-19 infection before it causes harm.

For example, this type of technology is used for the hepatitis B vaccine because the hepatitis b virus cannot be grown in vitro. 

Clinical trial results

The phase 3 clinical trial examined two different dosing regimens that give significantly different results.

The first dosing regimen (n=2741) used a half-dose for the first injection followed by a full dose at least one month later. This resulted in a vaccine effectiveness of 90%.

This regimen actually resulted from a dosing error early in the clinical trial. The study researchers noticed a lower incidence of minor side effects early in the trial, and it was determined that it was caused by an accidental dosing error. AstraZeneca decided to proceed with the lower first dose and give the normal second dose. This is why science is amazing, you can find data even if the experimental design had an error.

The second regiment (n=8895) used two full doses given at least one month apart. This regimen resulted in a 62% effectiveness.

The combined analysis from both dosing regimens (n=11636) resulted in an average effectiveness of 70%. 

According to the study protocols submitted by AstraZeneca, there should be another 20,000 participants in the UK and Brazil before the study is completed. In addition, similar studies are underway in the USA, Japan, Russia, South Africa, Kenya, and Latin America with planned trials in other European and Asian countries. AstraZeneca plans to have a total of 60,000 participants in its phase 3 clinical trials (remember, half do not receive the vaccine).

As I’ve reminded readers several times, this is more of the infamous peer-review by press release. At this time, no one has access to the data except AstraZeneca, so we should continue to be skeptical about these results until an unbiased group of scientists can review the results and give us their recommendations.

AstraZeneca has stated that it will seek an emergency use authorization (EUA) from the World Health Organization, although that would not have any effect in countries with strong drug regulation such as the EU and USA. If they seek a EUA in the USA, they will probably be required to have their vaccine clinical trial data reviewed by the Vaccines and Related Biological Products Advisory Committee (VRBPAC) as was required for the Pfizer vaccine recently. 

Advantages of the AstraZeneca vaccine

The vaccine also requires two doses, similar to the ones from Moderna and Pfizer, so there’s no real difference there.

However, there are two significant differences between the AstraZeneca, Pfizer, and Moderna COVID-19 vaccines. First, because the AstraZeneca vaccine utilizes known vaccine technology, there might be easier acceptance of its safety and effectiveness among scientists and an easier path to final regulatory clearance across the world. Although the mRNA vaccines should not be concerning because of how they function, they are still new technologies and will require more evidence to support safety especially.

Second, the AstraZeneca vaccine can be stored in normal refrigerators and can be shipped more easily than the mRNA vaccines which must be shipped mostly at very cold temperatures. This will give the AstraZeneca vaccine a significant distribution advantage.

The AstraZeneca COVID-19 vaccine probably would move to the number one position on my list of vaccines because of the technology and distribution advantages, but it will probably be the third to be available in the USA behind the ones from Pfizer and Moderna. However, it may be the first vaccine in the UK and Europe (although the Pfizer vaccine, because of its partnership with a German biotechnology firm, may still be first in Europe).

We might be hearing about other vaccines that show high effectiveness in clinical trials before the end of the year. Stay tuned.




Michael Simpson

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