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Why do vaccine clinical trials sometimes stop or suspend operations?

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Pausing or suspending clinical trials occurs frequently in the development of new medications and vaccines. This is because every clinical trial is overseen by a data and safety monitoring board that routinely looks at data from the different trial phases to see if there are any harmful or adverse issues happening in trial participants. The board also monitors to see if there is any evidence of the vaccine being effective. If the board has any concerns at any point during a clinical trial, they will suggest stopping a trial until they can determine a) what caused the patient(s) to develop a harmful medical issue, b) if people receiving the vaccine in the clinical trials are doing much better than those who didn't, or c) if people who received the vaccine are doing much worse than the people who didn't. These prescheduled checks by the boards may sound alarming, but they occur frequently in all phases of clinical trials. As vaccines move into the third phases of clinical trials, in which they are given to tens of thousands of people, it is not surprising that one or more people develop a medical issue which may or may not be related to the vaccine itself. Lists of side effects that you see on medications stem from these clinical trial phases. Studies also have pre-set protocols and criteria that determine what events will cause them to pause or stop their research phases. They cannot ethically continue with the trial if they have reasons for concern about the health of clinical trial participants who have received their vaccines.

This article was published on
October 16, 2020

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Pausing or suspending clinical trials occurs frequently in the development of new medications and vaccines. This is because every clinical trial is overseen by a data and safety monitoring board that routinely looks at data from the different trial phases to see if there are any harmful or adverse issues happening in trial participants. The board also monitors to see if there is any evidence of the vaccine being effective.

If the board has any concerns at any point during a clinical trial, they will suggest stopping a trial until they can determine a) what caused the patient(s) to develop a harmful medical issue, b) if people receiving the vaccine in the clinical trials are doing much better than those who didn't, or c) if people who received the vaccine are doing much worse than the people who didn't.

These prescheduled checks by the boards may sound alarming, but they occur frequently in all phases of clinical trials. As vaccines move into the third phases of clinical trials, in which they are given to tens of thousands of people, it is not surprising that one or more people develop a medical issue which may or may not be related to the vaccine itself.

Lists of side effects that you see on medications stem from these clinical trial phases. Studies also have pre-set protocols and criteria that determine what events will cause them to pause or stop their research phases. They cannot ethically continue with the trial if they have reasons for concern about the health of clinical trial participants who have received their vaccines.

Context and background

Recently, a clinical trial for a vaccine created by Oxford University and AzstraZeneca (a pharmaceutical company) was paused due to safety concerns. This trial was in the phase three stage of development, and stopped as a patient developed "transverse myelitis" which caused neurological issues stemming from inflammation of the spinal cord. (At the time of writing this, this trial has resumed).

This trial participant received the vaccine and not a placebo (which is a harmless substance that has no impact on a person, and is used to compare results of active vaccines in clinical trials). However, it is unknown whether or not the patient's illness occurred because of the vaccine they were given, or some other medical issue. Either way, the safety board recommended stopping the vaccine, which often occurs when vaccines reach the later stages of clinical trials.

On October 12, 2020, Johnson & Johnson announced that a phase 3 clinical trial of its Janssen COVID-19 vaccine candidate was paused due to "unexplained illness" in one participant. Johnson & Johnson stated that is is following its prespecified guidelines on when to pause studies due to reports of an unexpected serious adverse event (SAE), so there can be a "careful review of all of the medical information before deciding whether to restart the study."

This entry was updated with new information on October 13, 2020.

Resources

  1. AstraZeneca Covid-19 vaccine study put on hold due to suspected adverse reaction in participant in the U.K. (STAT)
  2. The ethics of pausing a vaccine trial in the midst of a pandemic: a conversation with Ruth Faden (STAT)
  3. One of the leading coronavirus vaccine trials is currently paused. Prominent vaccine researchers tell CNN that's unusual (CNN)
  4. A leading coronavirus vaccine trial is on hold: scientists react (Nature)
  5. Oxford's COVID vaccine trial "back up and running" after brief pause for safety check (CBS)
  6. BMS, Merck and Pfizer Join List of Companies Pausing Some Clinical Trials During Pandemic (BioSpace)
  7. Learn About Clinical Studies (ClinicalTrials.Gov)
  8. Why AstraZeneca just paused its coronavirus vaccine trial (LiveScience)
  9. Experts Say It’s a Good Sign That a COVID-19 Vaccine Trial Was Paused. Here’s Why (Healthline)
  10. Johnson & Johnson pauses Covid-19 vaccine trial after 'unexplained illness' (CNN)

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