“I’d like to stress these events appear to be extremely rare. However, covid-19 vaccine safety is a top priority for the federal government, and we take all reports of adverse events following vaccination very seriously,” said Janet Woodcock, acting commissioner of the Food and Drug Administration, who said the investigation would move forward rapidly and could conclude in days.
Woodcock and other federal health officials stressed that one reason to pause the use of the vaccine was to make sure health-care professionals were aware that blood clots potentially associated with a vaccine should not be treated with a conventional drug, heparin, which could exacerbate the clots.
All six cases in the United States occurred among women between the ages of 18 and 48, and symptoms occurred six to 13 days after vaccination, according to a statement issued by the Food and Drug Administration and the Centers for Disease Control and Prevention. One vaccine recipient died and another is in critical condition, an FDA official said Tuesday. The person in critical condition was treated with heparin, according to a person familiar with the situation who spoke on the condition of anonymity. A CDC official said two of the six patients have been discharged and three remain in the hospital.
With so few cases, regulators and clinicians still face many unknowns about whether there are particular risk factors that make people susceptible to the reactions.
Peter Marks, a top vaccine official at the FDA, said the clots are extremely similar to a highly unusual set of symptoms detected among people who received the AstraZeneca and University of Oxford vaccine: blood clots paired with low levels of platelets, blood cells involved in clotting. European regulators and scientists have determined that syndrome is possibly triggered by an immune reaction to that vaccine, which uses a similar technology to the Johnson & Johnson one to protect against covid-19.
There is not yet a clear explanation for the clots, but one leading theory is that a component of the vaccine — it isn’t certain which one — triggers an immune reaction. Investigations of the cases after use of the AstraZeneca and Oxford vaccine showed that people developed antibodies that bind to platelets, causing them to be activated and cleared in some people, while also promoting clotting. A similar reaction has been documented to the drug heparin.
Marks noted that the normal rate of brain blood clots in the general population was 2 to 14 per million people per year. Hormonal birth control can increase the risk of such clots, but Marks said there was no clear link in the cases so far. What made the clots particularly unusual was the low platelets associated with them, which suggest the immune system is reacting to the vaccine — something virtually unseen in healthy young individuals, according to Gowthami Arepally, associate professor of pathology at Duke University School of Medicine.
“There are two dual competing concerns I have with these reports: one, obviously, is that the actual fatalities and complication rates being described in healthy individuals getting the vaccine. The competing concern I have is that will it really add to the anti-vaxxer sentiments, that vaccines are not safe,” said Arepally, who is working as a consultant to AstraZeneca to help the company review the cases and the science around its clotting events.
“The overwhelming majority [of people vaccinated] are benefiting, but obviously we really need to identify the causes and the reasons why these rare complications are occurring,” Arepally said.
Health officials said people who have received the Johnson & Johnson vaccine who develop severe headache, abdominal pain, leg pain or shortness of breath within three weeks after vaccination should contact their doctor. They should not be treated with heparin, a commonly used blood thinner that could exacerbate the clot.
The decision to pause vaccination requires regulators to assess the risks and benefits of a rare side effect and the risk of covid-19, the illness caused by the coronavirus. The CDC will hold a meeting Wednesday of its Advisory Committee on Immunization Practices to review the cases and assess their potential significance, the statement said. The FDA will continue to investigate the cases.
“Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” the statement said. “This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot.”
Regulators in the United Kingdom, for example, found that the risks of covid-19 were greater than the risks posed by the AstraZeneca-Oxford vaccine to all age groups except for adults under age 30 and restricted use of the vaccine in that group. Various countries have imposed restrictions on the vaccine, reserving it for older people or discontinuing its use.
“I think it’s the prudent thing to do. I think it’s real — this is a rare, but real association,” said Paul A. Offit, a vaccine specialist at Children’s Hospital of Philadelphia.
The type of clot, called cerebral venous sinus thrombosis, was seen in combination with low levels of blood platelets, the agencies said. Treatment is different from what might typically be administered; while usually an anticoagulant called heparin is used to treat blood clots, it is dangerous to give heparin in this situation. Alternative treatments need to be given, they said.
The rare blood clots, paired with low levels of platelets, were first detected in people in Europe who had received the vaccine developed by AstraZeneca and the University of Oxford. European regulators said it was “plausible” that the clots were linked to that vaccination and have been reviewing four similar clotting cases after vaccination with the Johnson & Johnson vaccine, which uses a similar technology.
The clots have not been associated with the Moderna and Pfizer-BioNTech vaccines, which rely on a different technology, and those vaccinations are continuing.
In a statement, Johnson & Johnson spokesman Jake Sargent said the company shares all adverse event reports about individuals who receive the vaccine with health authorities.
“At present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine,” Sargent said. “We continue to work closely with experts and regulators to assess the data and support the open communication of this information to healthcare professionals and the public.”
European regulators in their investigation of the AstraZeneca vaccine said that out of 34 million people vaccinated, 222 cases of clots had been reported. There were at least 18 deaths.
Dan Barouch, a vaccine expert at Beth Israel Deaconess Medical Center in Boston who has been developing the technology used in the Johnson & Johnson vaccine for years, said in an email last week that there were a number of biological differences between the viral vectors, called adenoviruses, that are being used in the two vaccines.
The AstraZeneca vaccine uses an adenovirus that normally infects chimpanzees, while the Johnson & Johnson adenovirus normally infects humans.
“As such, issues that arise with one [adenovirus] vector do not necessarily apply to a biologically very different vector,” Barouch said.
White House covid-19 coordinator Jeff Zients said the call for a pause action was “taken an abundance of caution.”
“This announcement will not have a significant impact on our vaccination plan: Johnson & Johnson vaccine makes up less than 5 percent of the recorded shots in arms in the United States to date,” Zients said.
One of the cases happened in a Nebraska woman in her late 40s, who experienced a blood clot two weeks after receiving the Johnson & Johnson vaccine and received treatment at the Nebraska Medical Center in Omaha, according to state and federal health officials. The woman remains hospitalized, state officials said Monday.
Johnson & Johnson has committed to delivering 100 million doses of vaccine for distribution in the United States before the end of May and has said it can produce 1 billion doses globally by the end of the year. Its vaccine has been seen as a key component of the nation’s drive toward providing enough shots for all adults, especially because it requires only one shot.
The United States has banked on an increasing supply of Johnson & Johnson vaccine throughout 2021. The Biden administration brokered a deal with Merck to produce raw vaccine substance for Johnson & Johnson beginning in the second half of the year, and to help with finish and filling into vials as soon as next month.
The government and the companies have not disclosed how many doses would be available under that agreement, but it would set up a major production pipeline for the United States and potentially exports to other countries. Globally, Johnson & Johnson has agreed to sell 500 million doses to developing nations via the Covax purchasing agreement, which is affiliated with the World Health Organization and is dedicated to steering vaccine to disadvantaged countries. Johnson & Johnson also has agreed to sell up to 400 million more doses to a group purchasing organization for African countries.
CVS and Walgreens announced they would pause using the Johnson & Johnson vaccine, and many states advised providers to stop administering the vaccine until the CDC advisory committee has met. State officials said they were not given any heads up about the decision to pause.
“We were not informed prior to the announcement,” said Michael Fraser, executive director of the Association of State and Territorial Health Officials. “We are assessing the impact in the states. We’re supportive of an abundance of caution, but we also need to balance getting everyone vaccinated as soon as possible.”
Nearly 7 million doses of Johnson & Johnson’s single-shot vaccine had been administered throughout the country as of Monday, according to CDC data. More than twice that amount, about 16 million doses, have been delivered to states and territories, and through federal channels, since the beginning of March.
Despite a recent dip in shipments of Johnson & Johnson’s vaccine, clinics were scheduled for use of the shot throughout the country, from a Walmart drive-through in Bentonville, Ark., to a clinic at Canisius College in Buffalo. The one-shot option has proved popular for many people who have gravitated to its convenience, and states have deployed it in a variety of settings, from mass sites to targeted efforts to reach transient populations, such as the homeless.
Sites in a handful of states temporarily halted use of Johnson & Johnson’s vaccine last week after adverse reactions were reported, though these were immediate events consistent with common side effects of some vaccines, such as dizziness. The adverse reactions were reported in Colorado, Georgia, Iowa and North Carolina. CDC said it investigated and found no reason for concern.
The emergence of the rare blood clots fueled concerns that confidence in coronavirus vaccines could be shaken — with potentially serious consequences.
“It is good to be transparent about safety profiles of each of the vaccines, but also very important to put that safety profile in appropriate context. For most populations in most countries, the benefits of both of these vaccines significantly outweigh the risks,” said Krishna Udayakumar, a professor of medicine and director of the Duke Global Health Innovation Center. ”If the risk of rare adverse events lead to significant increase in vaccine hesitancy, we will have a much harder task to vaccinate the world.”
Isaac Stanley-Becker contributed to this report.
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