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What You Need to Know About the Johnson & Johnson COVID-19 Vaccine Trial Pause

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Key Takeaways

  • Johnson & Johnson has paused clinical trials of its COVID-19 vaccines as a result of an undisclosed illness in one of the participants. 
  • Serious adverse events (SAEs) are not uncommon. They are expected during vaccine trials.
  • Johnson & Johnson is the second company that has paused its vaccine trials during Phase 3. AstraZeneca paused its trial last month.

UPDATE: On October 23, Johnson & Johnson announced it would resume its Phase 3 clinical trial in the U.S.

Johnson & Johnson paused clinical trials of its COVID-19 vaccines on October 12 as a result of “unexplained illness” in one of the participants.

"Following our guidelines, the participant's illness is being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) as well as our internal clinical and safety physicians," the company said in a statement. "Adverse events—illnesses, accidents, etc.—even those that are serious, are an expected part of any clinical study, especially large studies."

They continued: “Based on our strong commitment to safety, all clinical studies conducted by the Janssen Pharmaceutical Companies of Johnson & Johnson have prespecified guidelines. These ensure our studies may be paused if an unexpected serious adverse event (SAE) that might be related to a vaccine or study drug is reported, so there can be a careful review of all of the medical information before deciding whether to restart the study.”

Johnson & Johnson’s Janssen Pharmaceutical Companies is developing the vaccine. While the company did not say what the illness was, they noted they “must respect this participant’s privacy.” Janssen also said in the statement they are committed to learning more about the participant’s illness before sharing additional details.

“SAEs are not uncommon in clinical trials, and the number of SAEs can reasonably be expected to increase in trials involving large numbers of participants," the statement says. "Further, as many trials are placebo-controlled, it is not always immediately apparent whether a participant received a study treatment or a placebo.”

What Does a Pause Mean? 

A pause is not necessarily a cause for concern, says Julian Rosenberg, Ph.D., assistant director for the Center for Biopharmaceutical Education and Training. In fact, it can be expected. 

“Currently, the pace of vaccine development against SARS-CoV-2 is occurring at an accelerated rate with the added pressure of intense global attention,” he tells Verywell. “Pauses in clinical trials simply demonstrate that our rigorous regulatory system is working.” 


Soma Mandal, MD
, a board-certified internist at Summit Medical Group in Berkeley Heights, New Jersey agrees.

"This is routine and should not cause alarm, since it is a part of the process in a randomized controlled trial," she tells Verywell. "There are standard review processes that are triggered when a potentially unexplained illness occurs. It indicates that the researchers are committed to the safety of the participants and the trial is being conducted to the highest standard.”

Johnson & Johnson was quick to point out in its statement that there is also a distinction between a study pause and regulatory hold.

"A study pause, in which recruitment or dosing is paused by the study sponsor, is a standard component of a clinical trial protocol," Johnson & Johnson said in the news release. "A regulatory hold of a clinical trial is a requirement by a regulatory health authority, such as the U.S. Food and Drug Administration. As outlined in our transparency commitments, we proactively disclose any regulatory hold of a pivotal clinical trial."

Johnson & Johnson is the second company that has paused its vaccine trials during Phase 3. AstraZenca’s trial was paused last month as a result of a patient developing spinal cord inflammation called transverse myelitis. While AstraZeneca resumed trials on September 12 in the U.K., the company’s clinical trials in other countries are still paused.

“Science rarely proceeds perfectly,” Rosenberg says. “If it did, we wouldn’t need to conduct experiments.”

What Is A Clinical Trial? 

At this point, you might be wondering how vaccine trials work. According to the Center for Virology and Vaccine Research (CVVR), “a clinical trial is a research study that is conducted with humans. Every medication that is licensed and approved for use by the FDA starts with clinical trials.”

Safety measures during clinical trials include regular check-ins to assess important vitals, including blood pressure, temperature, and, in some cases, blood work.

“Typically, adverse events are not uncommon and are often unrelated, but the researchers need to do their due diligence to make sure that there is nothing related to the vaccine itself,” Mandal says. “An independent committee reviews the data and then determines whether the vaccine caused the adverse event. If it is determined that there is no correlation, then the trial can continue.

Johnson & Johnson began clinical trials in July.

What This Means For You

A pause in clinical trials does not mean all progress toward a COVID-19 vaccine has been halted. Several pharmaceutical companies are continuing to take steps forward, ensuring a COVID-19 vaccine will ultimately be approved, manufactured, and available to the public.

What Are the Phases for Developing a Vaccine? 

As you might have gathered, the process of developing a vaccine has many phases—six, to be exact. According to the Centers for Disease Control and Prevention (CDC), Phase 1 involves small groups of people receiving the trial vaccine. In Phase 2, the clinical study expands and people who have characteristics (such as age and physical health) similar to those the vaccine targets receive the vaccine. During Phase 3, “the vaccine is given to thousands of people and tested for efficacy and safety,” the CDC notes.

From there, Phase 4, 5, and 6 include regulatory review and approval, manufacturing, and quality control, which involves the continuous monitoring of vaccinated people in order to ensure continued safety.

Vaccine-related symptoms and side effects are tracked on the Vaccine Adverse Event Reporting System (VAERS), a national vaccine safety surveillance program co-sponsored by the Food and Drug Administration (FDA) and the CDC.

Until a vaccine has been approved, continued safety protocols are recommended, including mask-wearing, regular hand washing, and maintaining safe social distance.

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