Does the AstraZeneca vaccine work?

AstraZeneca vaccine vials

Photo: oasisamuel (Shutterstock)

In addition to the Pfizer, Moderna, and Johnson & Johnson vaccines currently licensed for use in the US, several other vaccines are being used in other countries. One of them, the Oxford / AstraZeneca vaccine, is not yet licensed in the US and has been surrounded by controversy. Here is a summary of what we know.

How is this vaccine different from the others we have?

The Oxford / AstraZeneca vaccine uses an adenovirus (related to one of the viruses that causes the common cold) to carry a piece of DNA that encodes the instructions for the coronavirus spike protein. Our cells use that DNA to make the protein, and then our immune system recognizes the protein as an invader and produces antibodies that can recognize and fight the virus. This is a mechanism similar to the Johnson & Johnson vaccine. The Pfizer and Moderna vaccines, by contrast, use mRNA in a lipid bubble instead of DNA in a modified virus.

AstraZeneca vaccine is given in two doses and can be stored at refrigerator temperature for six months. It is also supposedly cheaper than the other vaccines, about $ 4 per dose instead of $ 10 for Johnson & Johnson or $ 20 or more for mRNA vaccines.

Where is this vaccine already being used?

According to The New York Times Vaccine Tracker, is authorized for emergency use in 46 countries plus the European Union and fully approved in Brazil. The United Kingdom, Australia, India, Canada and Mexico are among the countries where it is currently used.

Why is it not approved in the US?

The first large-scale trials of the vaccine, completed in December 2020, were the basis for several countries to authorize the vaccine and start using it. At the time, there was concern that the trials would be conducted differently in different countries, with different time periods between doses, and some participants received the wrong dose (although they turned out to be well protected from COVID despite the error).

The company conducted a more recent trial that included participants in the US AND announced the results of that test this week. They plan to apply to the FDA for an emergency use authorization, so this vaccine could end up being used in the US as well.

Did other countries not stop using it?

Earlier this month, several countries stopped using the AstraZeneca vaccine due to reports that some people who received the vaccine developed blood clots. (Blood clots can have a variety of causes and can also occur as a result of COVID.) However, an analysis showed that the development of blood clots in people who received the vaccine was no more frequent than in any equally large group of people. In other words, there was no reason to believe that the vaccine caused the clots. Vaccination programs resumed.

Is it as good as the other vaccines?

Like the other vaccines currently licensed in the US, it appears to protect 100% against life-threatening COVID cases, less effectively against mild and moderate cases of the disease. Full data has not yet been released, but the overall figures are comparable to the other vaccines we have.

Somewhat concerning, the numbers used in the AstraZeneca press release were out of date when published, and it appears that the company chose to use an effectiveness figure of 79% from a previous analysis, instead of the 76% that was calculated with the most recent data. Vaccine trials have an independent data safety monitoring board, which sounded the alarm about the discrepancy, but this shift in numbers doesn’t mean the vaccine is necessarily less effective, it just seemed to erode experts’ confidence in the company conducting the tests. We’ll learn more in a few weeks when the FDA is expected to release an informational document with its summary and interpretation of the US trial data.


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