More than 6.8 million doses of Johnson & Johnson's (JNJ 0.32%) COVID-19 vaccine have been administered to people in the U.S. That number won't change -- at least temporarily.
On Tuesday, the U.S. Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) issued a joint statement calling for a pause in the use of J&J's vaccine. Here are five answers to key questions you might have about this latest development.
1. Why did the CDC and FDA call for a pause?
The CDC and FDA recommended pausing the use of J&J's single-dose COVID-19 vaccine "out of an abundance of caution" after six cases were reported in the U.S. where individuals experienced severe blood clots after receiving it. All of the cases reported so far occurred in women between the ages of 18 and 48, with symptoms manifesting six to 13 days after they were inoculated.
The two agencies are reviewing the data related to these cases. In addition, the CDC is convening a meeting of an advisory committee on April 14 to review the data.
2. How could this vaccine cause blood clots?
During Johnson & Johnson's clinical testing of its vaccine, there were 25 cases of blood clotting among the total of around 40,000 participants in the study. However, 10 of those were in the placebo group. Although there were five more cases of blood clots among participants receiving the vaccine (including two incidents involve one patient), the company determined that there wasn't enough data to establish a clear link between the symptoms and the vaccine.
It's still too early to draw a hard conclusion that the vaccine causes these blood clots. There is a theory, though, that could explain why a vaccine of this type might lead to blood clots in rare cases.
A research team led by blood clotting expert Andreas Greinacher of the University of Greifswald in Germany thinks that it's possible that DNA from adenovirus vaccines could bind to a protein called platelet factor 4 (PF4). This could then trigger the production of antibodies against PF4, which then sets the stage for blood clots to form. A variation of this theory is that such antibodies already are present, and that the adenovirus vaccines boost those antibodies.
3. Has this issue occurred with other COVID-19 vaccines?
Similar extremely rare blood clotting issues have occurred in people who were inoculated with AstraZeneca's (AZN 1.29%) COVID-19 vaccine in Europe. U.K. authorities even recommended that individuals under age 30 receive a vaccine other than AstraZeneca's if possible. Both Johnson & Johnson's and AstraZeneca's vaccines are delivered using adenoviruses. AstraZeneca's vaccine has not yet received emergency use authorization in the U.S.
CDC Principal Deputy Director Anne Schuchat stated that the agency has not seen any reasons for concern about blood clotting with the COVID-19 vaccines marketed by Pfizer (PFE 1.31%) and Moderna (MRNA 1.06%).
4. Will J&J's vaccine become available again?
It seems highly likely that the pause for Johnson & Johnson's vaccine will only be temporary.
The CDC and FDA recommended the use of Johnson & Johnson's COVID-19 vaccine be paused while a review of reported cases of blood clotting issues is undertaken. The agencies specifically stated that this pause was important to make sure that healthcare providers are aware of the potential for the issues and "can plan for proper recognition and management due to the unique treatment required with this type of blood clot."
The process shouldn't take very long. Acting FDA Commissioner Janet Woodcock stated that the review of Johnson & Johnson's COVID-19 vaccine will only take a few days.
5. What does this mean for J&J and other vaccine makers?
The negative news for Johnson & Johnson has already provided boosts for the share prices of Moderna (MRNA 1.06%), Novavax (NVAX -2.97%), and BioNTech (BNTX 0.97%). All three biotech stocks jumped Tuesday. However, those gains will probably be short-lived if the CDC and FDA quickly establish guidelines that allow J&J's vaccine to be administered again.
Over the longer term, though, potential safety issues associated with adenovirus vaccines could be more problematic for Johnson & Johnson and AstraZeneca. After the urgency of quelling the pandemic is no longer a factor, governments will likely prefer COVID-19 vaccines with higher efficacy and better safety profiles. That could be good news for Pfizer, BioNTech, and Moderna, as well as Novavax (assuming its vaccine wins emergency use authorization).