On Tuesday morning, U.S. health officials recommended a break in using Johnson & Johnson’s COVID-19 vaccine as they investigate six reports of blood clots in women ages 18 to 48. One of them died and a second is hospitalized in critical condition.
As of Monday, 6.8 million people in the United States had received the vaccine with no other serious side effects reported.
Experts have yet to determine how much, if anything, the vaccine is responsible for clots. However, the investigation follows action by European regulators who concluded that the vaccine manufactured by AstraZeneca may also be the cause of a similar and extremely rare bleeding disorder.
Public health experts from the US and Europe have emphasized that for most people, the benefits of Covid vaccines far outweigh the risks.
Several European countries last week restricted the use of the AstraZeneca-Oxford vaccine to older adults due to the rare occurrence of the blood disorder in younger people. The AstraZeneca vaccine was not approved in the United States.
What does this mean for people who recently received the Johnson & Johnson vaccine?
Fewer than one in a million J&J vaccines are currently being studied. If there is indeed a risk of blood clots from the vaccine – which has yet to be determined – the risk is extremely small. The risk of developing COVID-19 in the US is much higher.
The Food and Drug Administration (FDA) recommends that people who have received the Johnson & Johnson vaccine in the past three weeks see their doctor if they experience severe headache, abdominal pain, leg pain, or shortness of breath. People shouldn’t worry about mild headaches and flu-like symptoms for the first few days after vaccination. These are common and harmless side effects caused by the immune system’s defense against the coronavirus.
What is a break?
During clinical trials and after vaccines become widespread, experts keep track of the medical problems that arise in people who receive them. If an unusually large group of cases arise, regulators may decide to stop a study or stop using a vaccine for further investigation.
Breaks are frequent, and research usually shows the medical problems were a fluke. If research shows a vaccine poses a risk, regulators can write new guidelines about who should or should not receive it.
In this case, the FDA and the Centers for Disease Control and Prevention (CDC) recommend an interruption, and several states have already followed the agencies’ advice. Those who have temporarily suspended vaccine use include a growing number of states such as New York, Virginia and Ohio, as well as the CVS Health and Walgreens chains.
At a press conference Tuesday, federal officials said the government review would likely only take a few days. A CDC panel is expected to discuss the matter in a meeting on Wednesday.
What is the problem that led to the break?
Six women in the United States who received the Johnson & Johnson vaccine developed a rare blood clot disorder within two weeks of being vaccinated. In this disease, known as cerebral venous sinus thrombosis, clots form in the veins that drain blood from the brain. The results are “similar to those of a stroke,” said Anne Schuchat of the CDC.
Researchers studying a very similar disorder in AstraZeneca receptors in Europe say it appears to be caused by an intense immune system response to the vaccine, which makes antibodies that activate platelets, a part of the blood that is used to form normal blood clots helps to repair wounds. In addition to clots, abnormal bleeding occurs. European researchers have named the disorder identified there as “vaccine-induced immune thrombocytopenia”.
FDA’s Peter Marks said it was the unusual combination of clotting and bleeding that alerted regulators as a possible safety signal.
So far, researchers have failed to find a way to predict who will develop the disorder or identify underlying conditions that could indicate a susceptibility.
What is a blood clot?
A blood clot is a thick, jelly-like mass of blood that can block the circulation. Clots form in response to injury and can also be caused by many diseases, including cancer and genetic disorders, certain medications, and prolonged sitting or bed rest. Covid itself can cause serious coagulation problems. Clots that form in the legs sometimes break off and travel to the lungs or, rarely, to the brain, where they can be fatal.
How common are blood clots?
In the United States, between 300,000 and 600,000 people a year develop blood clots in the lungs or veins of the legs or other parts of the body, according to the CDC.
Based on this data, between 1,000 and 2,000 blood clots occur daily in the American population. When millions of people are vaccinated every day, some of these clots will appear in those who happen to receive the vaccines, regardless of the vaccine.
In the UK, around 1 in 1,000 people are affected by a blood clot every year, according to regulators.
However, the bleeding disorder that worries vaccine recipients is much less common and different from typical blood clots. In addition to clotting in the brain – called cerebral venous sinus thrombosis, or CVST (acronym in English) – all patients had remarkably low platelets, which made them prone to abnormal bleeding.
What does Johnson & Johnson think of the new cases?
On Tuesday, Johnson & Johnson announced that the company was aware of an extremely rare condition involving people with blood clots combined with low platelets in a small number of people who received their vaccine for COVID-19. “In addition, we have examined these cases with the European health authorities,” said the company in its statement. “We made the decision to proactively delay the launch of our vaccine in Europe.”
Is it the same problem with the AstraZeneca vaccine in Europe?
At the press conference on Tuesday, FDA’s Marks said the cases were “very, very similar.”
Both Johnson & Johnson and AstraZeneca use adenovirus to transport DNA into human cells and initiate the process of generating immunity to coronavirus. It is not yet known if this technology is causing the problem.
German researchers have speculated that the DNA in the vaccine could trigger the immune response in some people. However, the condition is so rare that researchers say patients likely have an individual, but unknown, biological characteristic that predisposes them to overreact.
Last month, European regulators began investigating similar cases of cerebral vein thrombosis related to low blood platelets. They concluded that the disorder was a very rare side effect of the AstraZeneca vaccine. It’s too early to know if the Johnson & Johnson vaccine is responsible for the same type of rare blood clot.
What are the symptoms of an AZ-Related Bleeding Disorder?
European regulators had advised vaccine recipients to seek medical help for a range of possible symptoms including leg swelling, persistent abdominal pain, severe and persistent headache or blurred vision, and small spots of blood under the skin of the eyes beyond the area of the skin.
However, these symptoms were so vague that there was an almost immediate increase in the number of patients in the UK emergency rooms worried about changing the description.
However, German researchers say vaccine recipients should be monitored for these symptoms. Blood tests can detect the antibodies.
Is there any treatment for the disorder?
Doctors in Germany and Norway have treated patients with blood-thinning drugs to stop the clot from growing and intravenous immunoglobulin, which can help remove the wrong antibodies that are causing the problem.
Researchers in that country and federal health officials in the US on Tuesday advised against the use of a traditional blood thinner, heparin, and opted for alternative medications. This is because the disorder is very similar to a rare syndrome caused by heparin, and heparin can make the situation worse in these patients.
Heparin could “do a lot of damage,” said Marks.
German researchers have emphasized that treatment should be started as soon as possible, as the disease can worsen quickly.
Does this risk mainly affect women?
It is not yet known. The six cases studied in people who received the J&J vaccine involved women. However, this number is so small that it is impossible to draw firm conclusions.
In Europe, it initially appeared that women were at an increased risk of blood clots associated with the AstraZeneca vaccine, although some cases involved men who had received the vaccine.
On closer inspection, it was found that in some countries more women overall received the vaccine because they are overrepresented among healthcare workers. UK regulators now say they have no clues as to whether men or women are more likely to be affected by blood clots.
Are rare clots associated with Moderna and Pfizer-BioNTech vaccines?
The FDA did not find any similar cases in people who received the Moderna or Pfizer-BioNTech vaccines.
However, low platelet counts have been reported in a small number of patients who received the Moderna, Pfizer-BioNTech and AstraZeneca vaccines. One recipient, a Florida doctor, died of a cerebral haemorrhage when his platelet counts could not be restored and others were hospitalized. U.S. health officials have announced that the cases are being investigated, but have not reported the results of those reviews and have not yet indicated a link to the vaccines.
Benjamin Mueller contributed to the reporting.
Denise Grady has been a science reporter for The Times since 1998. She wrote Deadly Invaders, a book about emerging viruses. @nytDeniseGrady
Carl Zimmer is the author of the Matter column. He has published fourteen books including Life’s Edge: Finding What It Is To Be Alive. @carlzimmer | Facebook