An advisory committee for the Centers for Disease Control and Prevention declined to vote on the fate of Johnson & Johnson’s COVID-19 vaccine Wednesday, likely leaving in place a pause on the vaccine’s use until the committee reconvenes in seven to 10 days.
The CDC’s Advisory Committee on Immunization Practices, or ACIP, expects that the coming week or so will provide additional data and analyses on the vaccine’s potential risks. Until it has more information, ACIP opted to provide no new recommendations on the use of the vaccine.
On the table, however, was everything from recommending against use of the vaccine altogether; recommending that only certain groups receive the vaccine, such as only men or only people over a certain age; or recommending that the pause be lifted and use continue in all adults as before.
In a hearty discussion Wednesday afternoon, ACIP members said they simply didn’t feel they had enough information on updated vaccine risks to vote one way or the other on any of the possible usage recommendations.
ACIP gathered for the emergency meeting Wednesday after the CDC and the Food and Drug Administration abruptly announced on Tuesday that they were pausing use of the Johnson & Johnson vaccine. The agencies linked the vaccine to six illnesses involving an unusual combination of dangerous blood clots and low platelet levels. One person died from their condition and another is in critical condition.
The cases are extremely rare, with the six occurring among more than 6.8 million people vaccinated with the Johnson & Johnson vaccine. However, the cases closely resemble a very rare side effect seen in some people who have received AstraZeneca’s COVID-19 vaccine, which uses a similar adenovirus-based vaccine design.
With both vaccines, authorities noted unusual cases of cerebral venous sinus thrombosis (CVST), coupled with low blood levels of blood platelets (thrombocytopenia). CVST is a rare type of stroke in which a clot prevents blood from draining out of the brain. Platelets are the cell fragments in blood that stick together to form clots. Typically, low levels of platelets lead to bleeding, not clotting conditions, like CVST. In fact, it’s such an unusual combination that it’s unclear how often CVST even occurs in combination with thrombocytopenia in the absence of the vaccines. As such, researchers and public health experts have struggled to estimate the potential increased risk of developing this combination after taking either of the vaccines.
However, there’s a clear pattern emerging in these extremely rare, vaccine-linked cases—and researchers speculate that the vaccines may be triggering an aberrant immune response. A similar condition is seen rarely in patients given the blood thinner heparin. For reasons researchers don’t entirely understand, a small number of patients given heparin produce antibodies that attack a common platelet protein called Platelet Factor 4, or PF4. These antibodies activate platelets, leading to a hyperclotting state, while also promoting platelet clearance, dragging down platelet levels.
So far, many of the people who developed blood clots and thrombocytopenia after receiving the AstraZeneca vaccine also tested positive for antibodies against PF4, even though they were not given heparin. In the ACIP meeting today, CDC researchers noted that five of the six people with clotting cases linked to the Johnson & Johnson vaccine also tested positive for antibodies against PF4. The sixth case wasn’t tested.
There were other intriguing details revealed in the meeting as well. All six of the cases reviewed by the CDC and FDA were in white women between the ages of 18 and 48. This has led some people to speculate that for these women in the child-bearing age range, the blood clots could be related to the use of birth control pills, which carry their own risk for clotting. However, according to the data discussed in the ACIP meeting, only one of the six affected women was taking birth control pills.
Moreover, an analysis by scientists at Johnson & Johnson found a seventh case of CVST with thrombocytopenia in one of their clinical trial participants—a male participant. The previously healthy 25-year-old man developed CVST, low blood platelets, and tested positive for anti-PF4 antibodies after taking the vaccine.
To date, CDC researchers and other scientists have found no obvious pattern of risk factors for developing the life-threatening blood clots and low platelet levels.
But, CDC researchers and ACIP members expect they may see more cases emerge in the coming days. As noted in today’s meeting, the combination of CVST and thrombocytopenia tends to occur six to 13 days after vaccination. However, a little more than half of all doses of Johnson & Johnson vaccine that have been administered in the US to date were administered in the past two weeks. Specifically, prior to March 30, there were 3.47 million Johnson & Johnson doses administered in the US, or 48 percent of all doses administered to date. Between March 30 and April 13, there were 3.77 million doses administered, or 52 percent of all doses administered. That suggests that, despite the pause in vaccine use, there may be more cases detected in the coming weeks, particularly with lags in clinical reporting.
With the sparse data analysis so far and the potential for more cases and data to arise shortly, the ACIP opted to hold out a little longer before making any recommendations. Their position is a difficult one. They’re trying to balance safety concerns with the urge to vaccinate people as quickly as possible against the deadly pandemic coronavirus, particularly as virus variants emerge and spread. They were also sensitive to the reality that the adenovirus-based vaccines (made by Johnson & Johnson, AstraZeneca, and others) are more likely to be used in vulnerable populations and developing countries. The pauses and drama around these vaccines in places like the US and EU could increase vaccine hesitancy in populations with few other vaccine options.
For the US population overall, however, CDC researchers noted in the meeting today that the country’s vaccine supply is still strong. Even with the extended Johnson & Johnson pause, the US has steady supplies of mRNA vaccines from Moderna and Pfizer-BioNTech.