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Here’s What to Know About AstraZeneca’s COVID-19 Vaccine

What you need to know about the AstraZeneca vaccine.


All of the 124 million-plus COVID-19 vaccines that have been administered in the United States thus far have been of the Pfizer, Moderna, and Johnson & Johnson varieties.

But Americans might soon have another option, a shot developed at Oxford University and manufactured and sold by the British-Swedish pharmaceutical-biotech company AstraZeneca. But allegations that AstraZeneca may have misrepresented efficacy data and concerns that it could cause blood clots has derailed the rollout.

Here’s why the vaccine is still likely headed to the states, how it works, information on the data mishandling, updated data that shows its true efficacy, and what kind of impact it will have on the country’s return to something resembling normalcy.

What’s the controversy with the vaccine?

In the waning days of March, AstraZeneca released better-than-expected interim results from a new study that found its vaccine reduced symptomatic COVID-19 disease by 79 percent and severe COVID-19 and hospitalization by 100 percent. AstraZeneca said the vaccine was equally effective in people over 65.

“This analysis validates the AstraZeneca COVID-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus,” said Ann Falsey, a professor at the University of Rochester School of Medicine and co-lead investigator of the study.

However, shortly after the data was released, U.S. health officials immediately flagged the study as potentially having misleading data that overstated the efficacy of the vaccine. It’s likely that the vaccine is more like 69-75 percent effective at reducing symptomatic COVID risk, and still 100 percent effective at reducing hospitalization or serious illness.

North of the border, Canada has paused the administration of the AstraZeneca vaccine for people under the age of 55 following concerns that it could be linked to rare blood clots, with new data from Europe suggesting that risk is closer to 1 in 100,000 than the 1 in 1,000,000 it was previously thought to be.

Is the vaccine still effective?

Yes. The controversy over the vaccine’s efficacy is not about whether or not it is effective at all — but how effective it is at preventing symptomatic COVID-19 disease.

What the new data says about the AstraZeneca vaccine’s efficacy

After the bungled rollout, AstraZeneca updated the data surrounding the vaccine. The vaccine is 76 percent effective in preventing symptomatic illness in most people, dropping from the 79 percent efficacy the company touted in the misleading data. It is also, rather surprisingly, more effective in adults over 65, jumping from 80 to 85 percent efficacy with the full data. It is also 100 percent effective against serious illness.

What makes the AstraZeneca vaccine different from the existing options?

While it’s also a two-dose vaccine like the Moderna and Pfizer vaccines, the AstraZeneca version doesn’t use particles of messenger RNA to prompt cells to manufacture the spike protein that protects against COVID-19. Instead, it contains a modified version of the common cold virus to transfer the genetic code for the spike protein into recipients’ cells. It’s similar to the mechanism employed by the one-dose Johnson & Johnson vaccine, which was given emergency use authorization by the FDA at the end of February, though it uses a different virus as its Trojan Horse.

When could the AstraZeneca vaccine be approved? And what will its impact be?

AstraZeneca will apply for FDA authorization in the first half of April and, if approved, the company says they can deliver 30 million doses to the U.S. immediately and 20 million more within a month of approval. Another supply chain delivering tens of millions of vaccines to the U.S. is sorely needed, as only Alaska, Mississippi, and West Virginia have been able to toss out eligibility requirements, with other states limited at least in part by limited supplies of the vaccine.

This influx of doses will help states comply with Joe Biden’s promised directive to all states that a vaccine will be available to all adults by May 1. It could also help make the president’s promise of a close-to-normal Fourth of July a reality.