Speed bumps: part two
When it comes to vaccines, how safe is safe enough?
Since I wrote my previous article on the Oxford/ AstraZeneca vaccine for Covid-19, reports of blood clots associated with the vaccine have continued to come in. Although they still say that the link is “possible”, the European Medicines Agency now reports 86 cases of two types of rare blood clot among the 25 million people who have received the vaccine in the European Union and Britain. Of those 86 people, 18 have died. The numbers quoted by Britain’s Medicines and Healthcare products Regulation Agency are different – 79 cases and 19 deaths, perhaps due to how cases are defined, but the picture is similar. The blood clots occur within a couple of weeks of receiving the first dose of the vaccine and are rare, affecting around 4 people per million vaccinated. However, the death rate is high among those who are affected.
It’s a frightening development in what is already a frightening time, with cases of Covid-19 increasing again in many countries.
Despite this mounting evidence, the vaccine continues to be recommended and used. Are some countries so desperate to vaccinate their citizens that they are prepared to overlook deadly side effects? The short answer is yes, they are, but it’s not quite as simple as that. No decision that we make is without risk, and until we look at the bigger picture it’s hard to know what the right action is.
Different countries are taking different approaches, which adds to the confusion. The European Medicines Agency stated that the benefits of the vaccine outweigh the risks, but has gone on to report increasing numbers of blood clots after vaccination. Despite the reassurances, Germany has suspended use of the vaccine in those under 60, while Canada has suspended use in those under 55. Britain has halted a trial of the vaccine in children, and people aged from 18-29 will be offered an alternative vaccine, if it is available in their area. Despite this, Britain hasn’t put age-specific restrictions in place for the vaccine.
The actions of Britain are perhaps the most confusing, but they may actually be the smartest, given the circumstances. The reasoning is explained by British virologist Dr Chris Smith in an interview with Kim Hill on Radio New Zealand. He explains that the clots are extremely rare – the chance of having a clot is about four in a million among people who receive the vaccine, while the chance of dying is one in a million. Although the evidence is still quite weak, the risk of blood clots does appear to be higher in people who are younger. As we all know by now, this is the opposite of Covid-19, which is much more dangerous in people who are older. Deaths from Covid-19 are extremely rare in younger people – although it’s hard to find precise numbers, in children the rate is around one or two per million, and it’s similar in people under 30 who don’t have underlying medical conditions.
And that, says Dr Smith, is precisely why Britain is using an alternative vaccine for people under 30. In that age group, the risk of dying from Covid-19 and the risk of dying from a blood clot is similar, so using the Oxford/ AstraZeneca vaccine isn’t worth the risk. But for older people living where the virus is prevalent, the chance of dying from Covid-19 is much higher than one in a million. That’s why, even as the evidence mounts that the Oxford/ AstraZeneca vaccine is causing potentially fatal blood clots, most health regulators continue to say that the benefits of the vaccine outweigh the risks.
Precisely why the vaccine could be causing blood clots isn’t immediately clear. A blood clot normally forms when a blood vessel is damaged. A type of blood cell, called a platelet, is activated in response to the damage and begins to stick to the damaged area of the vessel wall. Platelets then release proteins that help to trap more platelets, and the accumulation of platelets forms a clot that plugs the damaged part of the blood vessel.
But, in the people who have had blood clots after receiving the Oxford/ AstraZeneca vaccine, there’s something odd going on. The platelet levels in their blood are unusually low. This combination of clots and low blood platelets looks similar to a condition which can occur in people who take the blood-thinning drug heparin. Blood thinners are drugs that prevent, not cause, blood clots, but in rare cases, heparin can do the opposite of what it is supposed to. The cause is believed to be an immune response to the heparin. It’s possible that the situation is similar with the vaccine, although it will take much more research to know that for certain.
But the mechanism for how the vaccine may be causing clots is only one question. There’s another crucially important question – what is it about the vaccine that could be causing the clots? And in answer to that question, German respiratory disease expert Professor Tobias Welte has a worrying suggestion. He suggests that the clots could be related to the viral vector used in the vaccine. The viral vector is the chimp common cold virus that has been genetically modified to carry the gene for the Covid-19 spike protein. And it hasn’t just been used in the Oxford/ AstraZeneca vaccine. The Janssen/ Johnson and Johnson vaccine against Covid-19 uses a chimp common cold virus and the Russian Sputnik V vaccine is also based on the common cold virus. If the vector is the cause, Professor Welte suggests, then we can expect to see blood clots as a side effect of those vaccines as well.
Professor Welte’s comments, made on the morning of the 8th of April in Europe, were remarkably prescient. The very next day, the European Medicines Agency announced that it was investigating 4 cases of clots associated with the Janssen/ Johnson and Johnson vaccine in the United States.
Does this mean that the clots have something to do with the vaccines being genetically modified?
That’s a question that can’t be answered just yet. Scientists still aren’t certain that the vaccine is causing the clots. If the vaccine is the cause, then we need to know what component of the vaccine is responsible. We don’t yet know that it’s the genetically modified component of the vaccine – all we have is a hunch from an expert, and however eminent the expert is, a hunch is not evidence. Then we would need to know the mechanism by which that vaccine component was causing the clots.
All of this highlights just how tricky risk assessment can be. We are talking about extremely rare side effects affecting around four in every million people who receive the vaccine. With numbers like that, typical trials, which look at thousands or tens of thousands of people, just aren’t going to pick them up. It’s only now, as the vaccines are becoming widely used, that we are learning about these side effects.
As I follow the story of these blood clots in the overseas media, I’m struck, once again, by how lucky we are in New Zealand. In most countries, a slow vaccine rollout would have been deadly. In New Zealand, where the need to protect people from Covid-19 is less desperately urgent, it’s given us a chance to learn more about potential side effects.
In the case of the vaccine New Zealand is using, the Pfizer/ BioNTech messenger RNA vaccine, there have been some significant side effects, but nothing as mysterious as blood clots. Severe allergic reactions have occurred at a rate of about five per million doses administered with no deaths reported. While potentially lethal, these severe allergic reactions are a known side effect of all vaccines. For the flu vaccine and human papilloma virus vaccine, the rate is just over one in a million. But for the measles vaccine in children, the rate is 120 in a million. Apart from the severe allergic reactions, the evidence is mounting to say that the vaccine New Zealand is using is not linked to any other dangerous side effects. Blood clots haven’t been reported in association with this vaccine or with the other messenger RNA vaccine from Moderna. No vaccine is without any risk at all but the vaccines are a lot less dangerous than Covid-19.
This week, I had intended to talk more about the genetic modification technology used in the Oxford/ AstraZeneca vaccine. However I decided it was more urgent to look at the rapidly evolving situation with blood clots. I will write more about the use of genetic modification in vaccines in future articles.
The Turnstone comes out once a week. I write an original article once a fortnight and on alternate weeks I share some of my older writing that’s not yet on Substack, or some links related to the previous week’s article.
As always, let me know if you have any questions that you’d like me to answer through my articles.
Do you know someone who might enjoy The Turnstone? Please forward it to them.
Did you receive The Turnstone from a friend? You can subscribe and receive it directly every week.
Do you want to see more of The Turnstone? All of the stories can be found in the archive, here.