Does AstraZeneca’s Shot Cause Blood Clots?
Denmark halts use of AstraZeneca vaccine over concerns of blood clots.

Does AstraZeneca’s Shot Cause Blood Clots?

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Sam Fazeli, a Bloomberg Opinion contributor who covers the pharmaceutical industry for Bloomberg Intelligence, answered questions after Denmark and Norway suspended the use of some or all of the Covid-19 vaccine developed by AstraZeneca Plc and the University of Oxford amid concern over the risk of blood clots. This follows temporary suspensions of the shot in other European countries because of safety issues, as well as questions about how Astra-Oxford conducted vaccine trials and the shot’s effectiveness compared to other vaccines. The conversation has been edited and condensed.

A vaccine side effect like blood clots sounds serious. But this hasn’t been an issue in the U.K., where millions of Astra vaccines have been given without incident. Are health officials being overly cautious?

I don't think you can be too cautious, but there is a balance that needs to be struck. This is a massive vaccination effort and you need to be careful and assess any possible risk, but in a calculated manner. It’s unfortunate that it’s happening with the Astra vaccine. Even if they end up finding that the side effect had nothing to do with the vaccine, the noise when such events are announced is a lot louder than when the question is answered — and it adds to the skepticism around this vaccine, and possibly others. Health authorities are stuck between a rock and a hard place. If they don't take precautionary action, and there was some link, then they have put their population at risk. If they do, then it raises the risk of vaccine skepticism. The right way to do this, though, would be to connect with U.K. and other drug regulators first and ask them if they had seen any signals in the millions of people who have been vaccinated, just like you would go to the Centers for Disease Control & Prevention in the U.S. or Israeli health authorities if you had a suspected side effect with the Pfizer Inc.-BioNTech SE vaccine, given the millions of doses they have administered there. Did this happen? It’s not clear. We need a coordinated surveillance system here, which sadly doesn’t appear to be in operation in the European Union, given that even with regulators’ endorsement, some EU countries have gone their own way and temporarily suspended vaccinations.

Weren't there other issues with the Astra vaccine? It's less effective on the elderly? Trial results were muddy? The U.S. hasn't approved it yet. What is it about this shot?

Sure. It wasn't the best-designed trial and initially had equivocal data. But since then, new information from the trial and real-world data from England and Scotland have shown the effectiveness of the vaccine. One caveat is that this data is collected after just one dose. Is it less effective in the elderly? We can't tell from the trials as they did not have enough people over the age of 65 in the group. Real world data is showing good efficacy in the older population, but even then we are looking at data collected soon after vaccination when the protection would be expected to be quite high. So we need more information. But there is still the antibody data that was published last year showing at least as good a response in the elderly compared to the young. As for the situation in the U.S., I assume American regulators would like to see data from the trial that Astra is conducting there, which is much larger than the U.K. trial and has a very simple design that is comparable to the trials for the Moderna Inc., Johnson & Johnson and Pfizer-BioNTech vaccines (all approved in the U.S.). It is possible, however, that the Astra trial will show efficacy closer to that seen with the J&J shot, i.e., 72%, or even lower, rather than the 95% seen in the Pfizer-BioNTech and Moderna vaccines. This is because it is using a short time interval of four weeks between the two doses, whereas data from Astra-Oxford's U.K. trial showed a much better efficacy with a dosing interval of 12 weeks. But even if it is a lower efficacy, the key is to see how good it is at protecting against severe disease and death and assess its safety. That’s the gold standard.

Weren't there also clot issues with J&J's vaccine? What about that?

There was a so-called imbalance of thrombotic cases in the J&J trial, with 15 such cases in the vaccine group and 10 in the placebo group. These are too few cases to really suggest a link, but it’s something to pay special attention to once the vaccine is rolled out. Also, it’s notable that there was an imbalance in the incidence of Bell's Palsy in the Pfizer-BioNTech trial initially. That turned out not to be substantiated based on the massive safety database that the CDC has collected on millions of vaccinated people so far.

How about other vaccine side effects? There was that news earlier this year about elderly people in Norway who died after receiving the Pfizer vaccine.

Right - that caused a lot of angst for people and it turned out that it was largely driven by the age and frailty of the subjects. Again, there has been no imbalance of death in the U.S. CDC data after millions received the Pfizer-BioNTech shot. But this illustrates the point I made earlier: You heard a lot more about the issue as it unfolded, but when the authorities resumed vaccinations after having established no causal link, there was hardly any discussion of it. The initial scare reverberated more than the resolution.

Sam, you are set to get your first shot this month in London. If it's Astra, how worried would you be? Is there one vaccine you'd rather get over another?

I would take Astra’s shot in a heartbeat. And I am hopeful my response to the vaccine won’t be too different from that of the more than 11 million others who have taken it in the U.K. without unexpected side effects so far. Am I sure I won't be the odd one who ends up getting a very rare side effect, whatever that may be? No, of course not. But I really want to have a chance at getting some aspects of my normal life back, and vaccines are the only way of doing that. The potential reward outweighs any small risk.

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

Sam Fazeli is senior pharmaceuticals analyst for Bloomberg Intelligence and director of research for EMEA.

©2021 Bloomberg L.P.

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