- The FDA and CDC have recommended a temporary pause in the use of the J&J COVID-19 vaccine after reports of a “rare and severe” type of blood clot in six vaccine recipients.
- In the phase 3 clinical trial, the most common side effects seen with the J&J vaccine were pain at the injection site, headache, and flu-like symptoms.
- The FDA will continue to monitor the safety of the J&J vaccine as it’s rolled out to the American public.
On April 13, the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) called for a pause in the use of the Johnson & Johnson COVID-19 vaccine after reports of a “rare and severe” type of blood clot in six vaccine recipients.
All six cases involved women between the ages of 18 and 48, according to a joint statement issued by the agencies.
Symptoms occurred 6 to 13 days after they received this one-dose vaccine.
One woman died. A second woman has been hospitalized in critical condition, according to federal officials.
More than 6.8 million doses of the J&J vaccine have been administered in the United States.
The CDC’s Advisory Committee on Immunization Practices will meet on April 14 to “review these cases and assess their potential significance,” the statement said.
The statement also noted that these cases “appear to be extremely rare.”
Angela Rasmussen, PhD, a virologist at the Georgetown University Center for Global Health Science and Security, pointed out on Twitter that the rate of reported blood clots among Americans who received the J&J vaccine is lower than the rate of blood clots both in women taking oral birth control pills and in people hospitalized for COVID-19.
People who have received the J&J vaccine who develop headache, abdominal pain, leg pain, or shortness of breath within 3 weeks after vaccination should contact their doctor, according to the joint statement.
Pain at injection site seen in many people
In February 2021, the FDA issued an emergency approval for the one-dose COVID-19 vaccine developed by Johnson & Johnson’s subsidiary company Janssen Biotech.
As with the two mRNA vaccines approved in December, the J&J vaccine has mostly mild side effects that can be managed with rest or an over-the-counter pain reliever.
So far, there have been fewer cases of allergic reactions to the J&J vaccine compared with the Moderna-NIAID and Pfizer-BioNTech vaccines, although J&J reported in February that two clinical trial participants had a severe allergic reaction after receiving its vaccine.
The FDA will continue to monitor the safety of the J&J vaccine as it’s rolled out to the American public.
Before the FDA issued the emergency use authorization (EUA) for the J&J COVID-19 vaccine, scientists from the agency reviewed data from the company’s phase 3 clinical trials.
Dr. Bruce Y. Lee, executive director of Public Health Computational and Operations Research and professor of health policy and management at CUNY Graduate School of Public Health and Health Policy, said the side effects seen in those trials fall into two main categories.
“First are the injection site reactions. That’s usually pain, redness of the skin, or swelling at the injection site,” he said.
“And then there are systemic side effects: flu-like symptoms such as fatigue, muscle aches, nausea, and potentially fever,” he said.
Data from the clinical trials showed that around half of the people who received the vaccine had a local reaction. Pain at the injection site was the most commonly reported one, occurring in almost all cases.
Local side effects began on average 2 days after vaccination. Pain and redness lasted for 2 days on average, and swelling for 3 days on average.
The onset and duration of local side effects varied, but less than 3 percent of people had side effects that lasted longer than 7 days.
Severe local side effects were uncommon, with less than 1 percent of people having severe pain. A small number of people had reddening of the skin near the injection site or swelling.
All these local side effects were reported more often among people ages 18 to 59 compared with people 60 or older.
Headache and flu-like side effects common
Systemic side effects occurred in about 55 percent of people who received the vaccine.
The most commonly reported ones were headache, fatigue, and muscle pain, and in smaller numbers of people, nausea and fever.
These side effects began on average 2 days after vaccination. Fatigue, headache, and muscle ache lasted on average 2 days. Nausea and fever lasted on average 1 day.
The onset and duration of systemic side effects varied, although less than 2 percent of people experienced systemic side effects lasting longer than 7 days.
Less than 2 percent of the systemic side effects were severe, with the most common being fatigue, muscle pain, and fever.
All the systemic side effects were reported more frequently among younger adults compared to older adults. The one exception was nausea, which occurred at about the same rate in both groups.
Around one-fifth of people reported using a medication to relieve their pain or fever within 1 week of their vaccination. This was more common among younger adults.
How does J&J compare to the mRNA vaccines?
While it can be difficult to compare the efficacy of vaccines tested in different clinical trials under different conditions, Katelyn Jetelina, PhD, an assistant professor at the University of Texas Health School of Public Health in Dallas, said side effects are easier to compare.
“Because the clinical trials were large and randomized,” she said, “we are confident that these side effects aren’t due to individual variation, but rather closer to the ‘true’ experience for vaccinated adults.”
The type of side effects seen with the J&J vaccine are in line with those experienced by people who received one of the mRNA vaccines.
However, “in the clinical trials [for the J&J vaccine], fewer people reported side effects, relative to Pfizer or Moderna, especially if we compare J&J to the second dose of Pfizer or Moderna,” Jetelina said.
More than 80 percent of people who received the Moderna-NIAID vaccine experienced local reactions after either dose. It was about the same for the Pfizer-BioNTech vaccine. This is higher than seen with the J&J vaccine.
For the Moderna-NIAID vaccine, about 55 percent of people experienced systemic reactions after the first dose — similar to the J&J vaccine — but 80 percent experienced them after the second dose.
The Pfizer-BioNTech vaccine also had a higher rate of systemic reactions than the J&J vaccine, especially after the second dose.
Lee said the stronger side effects after the second dose of the mRNA vaccines is “probably because your immune system is primed from receiving the first dose.”
Clinical trials provide important information about the safety of vaccines, but the federal government continues to monitor vaccines after they're approved.
“Any time you have an adverse event from a vaccine, it’s important to report it,” Lee said, “because we really want to see how the vaccine behaves in a broader population and over time.”