Oxford COVID-19 Vaccine Trial on Hold

Phase 3 trials of the vaccine candidate have been halted while a ‘potentially unexplained illness’ is reviewed.

lab worker

Medically reviewed in September 2020

Updated on September 11, 2020

Clinical trials for a leading COVID-19 vaccine candidate called AZD1222, which is being developed by AstraZeneca and the University of Oxford, have been put on hold, according to a statement from the drug maker.

The vaccine—one of more than 160 experimental COVID-19 vaccines in development around the world—emerged early on as a leading contender in the global race to halt the spread of SARS-CoV-2, the virus that causes the disease.

AZD1222 is currently one of three experimental vaccines in phase 3 trials in the United States. AstraZeneca launched the final stage of its trial on September 1 with plans to test the vaccine in 30,000 healthy adults with diverse racial and ethnic backgrounds.

The first U.S. volunteers were inoculated at the University of Wisconsin School of Medicine and Public Health in Madison. AstraZeneca announced plans to add 50 participants each day after September 7.

The trial was abruptly halted on September 8, however, due to a possible adverse reaction in the U.K., which is now under review. Keep in mind, this is standard protocol, or what happens whenever a negative event is documented in a clinical trial. It’s also still unclear if this reaction is associated with the experimental vaccine, or if it’s an unrelated issue.

AstraZeneca did not initially provide specifics on the symptoms that the U.K. participant developed or when the trial would restart. During a private call on September 9, the drug maker’s chief executive, Pascal Soriot, reportedly told investors that the person experienced neurological symptoms that were consistent with transverse myelitis, an inflammation of the spinal cord.

Transverse myelitis is rare. In many cases, the cause of the condition is unknown but it may be triggered by viral, bacterial or other infections, immune system disorders, and other problems that destroy myelin (the fatty white substance wrapped around nerve cells).

People with transverse myelitis may develop a range of symptoms, including:

  • Weakness or pain in the arms and legs
  • Numbness, burning, coldness, or tingling in the legs
  • Bowel or bladder problems
  • Muscle spasms
  • Headache
  • Fever
  • Loss of appetite

The fact that the trial is on hold isn’t necessarily reason to lose hope. In fact, it shows that the researchers are keeping the safety of the vaccine top of mind.

"This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials," the company explained in a statement.

Early results were promising
In early-stage clinical trials, AZD1222 triggered “robust immune responses” among participants. The highly anticipated findings, which were published on July 20 in The Lancet, revealed that the vaccine triggered an increase in antibodies (proteins in the blood that help fight off infection) and a T-cell response. T-Cells also help the body fight disease.

The randomized Phase I/II trial included 1,077 healthy adults between the ages of 18 and 55. The scientists gave the experimental COVID-19 vaccine to 543 people. Of these, 533 received a single dose and 10 received two doses of AZD1222 one month apart.

The effectiveness of the experimental vaccine was assessed against a meningococcal conjugate vaccine that served as a control. Only the researchers knew which treatment the participants received.

The trials showed that neutralizing antibody responses were detected in 91 percent of the participants studied who received a single dose of AZD1222 and 100 percent of the participants who received the booster dose. A T-cell response was also induced in all of the participants studied, which was maintained two months after injection.

Many effective vaccines trigger both an antibody and a T-cell response.

How the vaccine works
The Oxford vaccine uses another type of harmless virus to deliver biological instructions for how to fight off the coronavirus that causes COVID-19.

The viral vector used in the vaccine is based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein—the protein the coronavirus uses to invade people’s cells.

Recombinant vector vaccines, such as AZD1222, act like a natural infection, which means they may be particularly effective in teaching the immune system how to fight germs. After vaccination, the surface spike protein is produced, which primes the immune system to attack COVID-19 if it ever infects the body.

The virus that causes the common cold in chimpanzees was genetically modified to make it “appear” more like SARS-CoV-2—but it can’t cause infections in people.

The early trial results showed that AZD1222 had only minor to moderate side effects, including pain, feeling feverish, chills, muscle ache, headache and malaise. These effects, however, were eased among participants who received acetaminophen to prevent them from occurring.

No serious negative reactions were reported during these initial trials.

The next steps
Though early results were promising, much larger Phase III trials are needed to determine if AZD1222 actually provides immunity to COVID-19.

In addition to the United States and the U.K., phase III trials were also underway in Brazil and South Africa. 

Meanwhile, AstraZeneca has already concluded agreements for at least 400 million doses of AZD1222 and has the capacity to manufacture capacity for one billion doses. The company has said it hopes to begin first deliveries by the end of 2020.

Back on May 21, the United States announced it secured 300 million doses of the experimental vaccine—nearly one-third of the first one billion doses the drug maker plans to produce.

The U.S. Department of Health and Human Services secured the vaccines by pledging up to $1.2 billion to accelerate the drug maker’s vaccine development program.

Article sources open article sources

The New York Times. “Coronavirus Vaccine Tracker.”
Pedro M Folegatti, MSc; Katie J Ewer, PhD; Parvinder K Aley, PhD, et al. “Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial.” The Lancet. July 2020.
AstraZeneca. “COVID-19 vaccine AZD1222 showed robust immune responses in all participants in Phase I/II trial.”
World Health Organization. “Vaccine Immunology.”
AstraZeneca. “AstraZeneca advances response to global COVID-19 challenge as it receives first commitments for Oxford’s potential new vaccine.”
Oxford University. “Trial of Oxford COVID-19 vaccine starts in Brazil.”
AstraZeneca. “AstraZeneca to supply Europe with up to 400 million doses of Oxford University’s vaccine at no profit.”
U.S. Department of Health and Human Services. “Trump Administration’s Operation Warp Speed Accelerates AstraZeneca COVID-19 Vaccine to be Available Beginning in October.”
National Institute of Neurological Disorders and Stroke. “Transverse Myelitis Fact Sheet.” March 2020.

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