Skip to content
Technology & Ideas

Is the AstraZeneca Vaccine Safe or Not?

Regulators in the U.K. and Europe still back the shot despite the risk of rare but potentially dangerous blood clots. Here’s what you need to know.

Benefits of the Astra shot still outweigh the risks … but there are risks.

Benefits of the Astra shot still outweigh the risks … but there are risks.

Photographer: Martin Bureau/AFP via Getty Images

Last month, several European countries suspended use of the AstraZeneca Plc Covid-19 vaccine amid safety concerns after some blood-clotting events that regulators feared might be tied to the shot. At the time, the U.K. — which had already distributed the vaccine to millions — didn't seem to have the same experience. That's changing. U.K. regulators are now signaling there may be a link to rare but potentially life-threatening clotting — especially among younger people — and are recommending that those under 30 receive the Pfizer Inc.-BioNTech SE shot or Moderna Inc. vaccine instead. European regulators are leaving this type of recommendation up to individual member states, and both European and U.K. regulators say the benefits of the Astra vaccine still outweigh the risks. Here, Sam Fazeli, a Bloomberg Opinion contributor who covers the pharmaceutical industry for Bloomberg Intelligence, answers questions about these recent developments and the potential risks.

Is there an increased risk of blood clotting with the Astra vaccine? How serious is it?

Yes. Given all the information shared by European Union and U.K. regulators, there is a reasonable chance that the AstraZeneca vaccine is associated with an increased risk of a rare condition that is characterized by blood clotting coupled with a fall in platelet counts. These divergent symptoms are what makes this a serious and difficult-to-treat reaction. The reported number in the EU calculates to about 1 per 100,000 vaccinations, which is about two to five times higher than the annualized rate you would normally expect in the general population.

How dangerous is this condition? Can it be diagnosed in time and is it treatable?

Unfortunately, several people have died because of these clots. The U.K. Has noted 19 deaths out of 79 cases after 20.2 million doses of vaccine as of March 31, with three of those under the age of 30. The diagnosis requires people to be aware of issues related to the clotting problem, including persistent headaches, unusual pin-point bruising and abdominal pain. So to a large degree it is reliant on individuals reporting the side effects for us to know the true incidence of this condition. What both the U.K. and EU regulators have said is that there is no clear scientific agreement on what the best course of therapy is as the disease is quite rare in terms of the concurrent appearance of clots and low platelets.

The U.K. recommends younger people take other vaccines, while the EU doesn’t go that far. This is confusing. Why risk it?

Well, the EU's European Medicines Agency has said that there is no clear correlation with any specific risk factor, though they did admit that younger people may be more at risk. The U.K.’s Medicines and Healthcare Products Regulatory Agency said that indeed the risk of the clots increases with decreasing age. I don't think it matters what the EMA says, each country in the EU will make its own decision and I expect them all to have some kind of age cutoff, as many do now.

Should the Astra shot be limited to the elderly?

That would be one way of doing it and that is what many EU countries have done. As noted above, the U.K. has gone with 30 as an age cutoff. But even if the risk of the rare side effects is similar in older people — which according to the U.K. it is not — the risk-benefit calculation is much clearer in the older population because it is at much higher risk of Covid-19 complications. The MHRA noted that 7.8% of people with severe Covid-19 get a pulmonary embolism, 11.2% get deep-vein thrombosis and there is a 1.6% risk of a stroke. Given the fact that most people who get severe Covid-19 are older individuals, it makes sense for them to receive the Astra shot now if it’s available rather than wait for another vaccine and risk contracting one of these serious health conditions.

There are other vaccines that use similar technology as the Astra shot. Are there implications about the risks involved with those vaccines?

Yes. I believe all vaccines like Astra’s that use an adenovirus as their delivery technology have to be observed very closely. These include Johnson & Johnson, Russia’s Sputnik V and China’s Cansino vaccines. The EMA did give data for the J&J vaccine suggesting three cases of the rare brain clots after 4.5 million doses, but I am not clear whether these were the same type seen after the Astra vaccine — i.e., concurrent with low platelets. As always, we are left gasping for more data from both the MHRA and EMA.

Might any of this have any bearing on U.S. approval?

Of course — especially for a country that doesn't really need the Astra vaccine. Why approve a vaccine that may have a rare side effect if you don't need it?

Sam, you received the Astra vaccine before this latest round of data became available. Knowing what you know now, would you still take it?

Well, it comes down to this: If I had no other option, what would I do? I think the answer is simple — I would take the Astra jab even now, especially given my age (shhhhh!!). As for where things stand now that I have already received my first shot, I will take a second Astra jab if that’s what is available. But if I knew that a second dose of the Pfizer-BioNTech or Moderna jab was just as good in terms of giving me protection against Covid-19 disease and it was possible for me to get that, then of course that's what I would prefer.

    This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

    To contact the author of this story:
    Sam Fazeli at mfazeli@bloomberg.net

    To contact the editor responsible for this story:
    Beth Williams at bewilliams@bloomberg.net