AstraZeneca shares fell more than 6% after close of trading Tuesday after the company announced it had suspended the late-stage of a potential coronavirus vaccine for safety reasons.
"This is a routine action that must be performed whenever any of the studies has a potentially unexplained disease while it is being investigated to ensure that the integrity of the studies is maintained. In large studies, diseases occur randomly, but they must independently verified to review carefully, "the company said in a statement to CNBC.
Attempts have been made to speed up the verification process to "minimize any impact on the test schedule".
"We are committed to the safety of our participants and the highest standards of behavior in our experiments," said the company.
According to a person familiar with the development, according to STAT News, out of “caution” after suspicion of serious side effects in a participant in the UK, researchers were told that the trial has been terminated.
It is unclear how long the process will take. AstraZeneca began its study late last month and is one of three companies currently in the late-stage on a potential vaccine. The other two are Pfizer and Moderna, both of which started trials in late July.
The US government announced on May 21 that it would pay AstraZeneca up to $ 1.2 billion for its experimental vaccine, which was developed in collaboration with researchers from Oxford University. The US will receive at least 300 million doses of the vaccine as part of its investment.
AstraZeneca's vaccine, called AZD1222, uses genetic material from the coronavirus with a modified adenovirus. It uses technology to make an experimental Ebola vaccine that was made available to people in the Democratic Republic of the Congo in late 2019.
In July, the company released data showing that its vaccine produced promising immune responses in an early study.
The vaccine was found to be well tolerated and, according to the researchers at the time, there were no serious adverse events. Fatigue and headaches are the most commonly reported, they said. Other common side effects were injection site pain, muscle pain, chills, and fever.
According to polls, Americans are already concerned about the safety of potential coronavirus vaccines.
According to a recent USA TODAY / Suffolk poll, two-thirds of voters say they will not receive the coronavirus vaccine once it becomes available.
–CNBC's Meg Tirrell contributed to this report.