When federal officials suspended the administration of the Johnson & Johnson vaccine after six cases of a rare coagulation disorder, one fatal, among the 6.9 million people who received the vaccine, many critics noted that the chance of ‘ a serious illness so rare was negligible – less frequent than being struck by lightning.
© Rick West / Daily Herald, via Associated Press
A mass vaccination site in Elgin, Illinois, was closed for a day because of the Johnson & Johnson vaccine.
But the roughly one-to-million rate is far from certain. Eventually, doctors may find that the vaccine is not responsible for the ailment. However, if the two are linked, it is also possible that the chance of an adverse effect will be greater, even if it remains low.
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“The numbers look pretty solid, like, ‘Oh, it’s ten,'” said Caitlin Rivers, an assistant professor at Johns Hopkins University who studies infectious diseases. She said epidemiologists deal with similar cases of uncertainty at the onset of disease outbreaks. “But these are estimates, and they will have to be refined, and they may have to be refined a lot, especially since they are a small number.”
How do we know how common this event is?
If there is a link between the vaccine and this rare syndrome, new cases are likely to emerge after the word is no longer available. Regulators have announced the interruption in part to let doctors know this syndrome exists; if people start searching, it is likely that they will find and report it. If the numbers are so low, the addition of a few more cases can increase the rate. (Over the past few days, Johnson & Johnson has reported two more possible cases, one in a woman and one in a man.)
If there is a link between the vaccine and the syndrome, more people who have already had shots may develop the clotting problem, as it appears to be within a few weeks after vaccination. About half of the Americans who received the Johnson & Johnson shot received it, according to government estimates this month. One of the reasons why the Center for Disease Control and Prevention Vaccine Safety Committee wants to wait longer before updating any guidelines on the shot is to see what happens to this group. Since the break was first recommended, the governance of Americans who got the shot increased to 7.7 million.
It may appear that only some sections of the population are at high risk for this problem, just as some populations are at greater risk of developing serious diseases. Most cases so far have been in women between 18 and 50. If we look at six cases in the population, the syndrome seems somewhat more common, but still very rare.
If more cases are reported, it is also possible that this gender pattern will disappear.
Dr. Tom Shimabukuro, a vaccine safety expert at the CDC, who presented figures to the vaccine safety council this week, said all current calculations were still ‘crude’.
How can we see that the blood clots would not occur anyway?
It’s hard to see now. Studies of such events usually compare people who receive a medication or vaccine with a control group of people who have not done so. With a rare disorder like this, the comparison cannot be easily made with clinical trials. Researchers are conducting a large-scale study of the health records of 12 million patients called the Vaccine Safety Datalink, comparing medical records of people who were vaccinated earlier with those who later get their shots – a system that does not rely on voluntary reporting. These results will take a while.
Researchers are also looking at what is called a background figure of serious events: the chance that someone may have a health problem, even if he or she has never received a vaccine. Comparing the events among people receiving a vaccine with the rate in the overall population may give an idea whether the outcome of a given patient may be due to the vaccination, or more likely just coincidental.
The tables above show the background figures for the specific type of blood clot that the authorities saw in the vaccinated patients – a blockage in the brain called a cerebral venous sinus thrombosis. These numbers are not a perfect comparison because there are no good background statistics for this type of blood clot combined with low platelets, the specific syndrome seen in the vaccinated women.
Women under 50 – the group at risk for the side effect of the vaccine – are also more likely to have these blood clots than to live than the general population.
What is a rate we need to take care of?
Many medications given to sick people can have serious side effects for some of those who take them. Physicians and patients regularly weigh such risks against the benefits of medical treatment.
Birth control pills with estrogen are regularly discussed this week because they are a common medication that carries a risk for blood clots. Lumps caused by birth control pills differ from the syndrome associated with the vaccinations of Covid, and some experts warn against comparing them directly. The form of blood clots caused by oral contraceptives usually forms in the bones of patients, not in their brains, but it can still be serious. The pills double the risk of such an event more than a typical woman, which means that between three and nine women out of 10,000 taking the pills for a year will develop a blood clot. (Pregnancy, the condition for which birth control pills are often prescribed to prevent, causes a greater risk of blood clots.)
“I would often say that the risk of getting blood clots with birth control pills is similar to a very serious reaction to penicillin,” said Dr. Raegan McDonald-Mosley, an obstetrician-gynecologist and CEO of Power to Decide, said. , a group willing to reduce unintended pregnancies. She regularly discusses blood clot risk with her patients and tells them the increase in risk and the overall extent of the risk. According to her, most patients choose their form of birth control based on other considerations.
Penicillin, a widely used antibiotic, causes severe allergic reactions between one in five patients for every 10,000 people who take it.
For vaccines, however, the threshold for safety is generally higher than for other types of medicine. As many researchers have noted, Covid-19 also puts people at risk for serious blood clots – far more than any possible estimate of the vaccine effect. But not everyone who is not vaccinated will get sick.
“The disease you happen to get and the vaccine you get by choice, and that makes it harder,” said Dr. Steven Black, an emeritus professor of pediatrics at Cincinnati Children’s Hospital, said.
For other vaccines, the risk of serious side effects is much lower than for contraceptive pills or penicillin – it usually occurs in less than 1 in every 100,000 who receive a given vaccine. The rate is “clearly much, much less than a drug would have tolerated,” said Dr. Nicola Klein, director of the Kaiser Permanent Vaccination Study Center, which is involved in the Vaccine Safety Datalink study.
Most other vaccines protect against rare diseases. In contrast, Covid-19 remains widespread in the United States and in many parts of the world. Given the severity of the disease and its spread, vaccination may now be higher than when such considerations are usually considered.
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Josh Katz contributed production.
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