Bigger problems quickly arose.
An AstraZeneca executive told Reuters on Monday that the company did not expect participants to receive half the dose. The British researchers conducting the trial there had initially wanted to give the full dose to the volunteers, but a miscalculation meant that they had mistakenly received only half a dose. The executive, Menelas Pangalos, called the mistake a “coincidence”, allowing researchers to come up with a more promising dosing schedule.
For many outside experts, this compromises the credibility of the results because tightly calibrated clinical trials were not designed to test the effectiveness of an initial dose at half strength.
The company’s initial announcement did not mention the accidental nature of the find.
In the statement attributed to Oxford, Ms Meixell, spokeswoman for AstraZeneca, said the error stemmed from an issue, which has since been resolved, with the way some of the vaccine doses were manufactured.
Then, on Tuesday, Moncef Slaoui, head of Operation Warp Speed, the US initiative to speed up coronavirus vaccines, noted another limitation in AstraZeneca data. On a call with reporters, he suggested that participants who received the initial half-strength dose were 55 or younger. Ms Meixell declined to say whether this was the case, noting that the data would soon be published in a peer-reviewed journal.
If the initial half-dose were not tested in older participants, who are particularly vulnerable to Covid-19, it would hurt AstraZeneca’s case for regulators that the vaccine should be cleared for emergency use.
Confused by all the technical terms used to describe how vaccines work and are studied? Let us help you:
- Adverse event: A health problem that arises in volunteers during a clinical trial of a vaccine or drug. An adverse event is not always caused by the treatment tested in the trial.
- Antibody: A protein produced by the immune system that can attach to a pathogen such as coronavirus and prevent it from infecting cells.
- Emergency use approval, license and authorization: Drugs, vaccines and medical devices cannot be sold in the United States without winning approbation of the Food and Drug Administration, also known as permit. After a company submits clinical trial results to the FDA for review, the agency decides whether the product is safe and effective, a process that typically takes several months. If the country faces an emergency – such as a pandemic – a business may instead request a emergency use authorization, which can be granted much faster.
- Background rate: How often a health problem, called an adverse event, occurs in the general population. To determine whether a vaccine or drug is safe, researchers compare the rate of adverse events in a trial to the baseline rate.
- Efficiency: A measure of the effectiveness of a treatment in a clinical trial. To test a vaccine against the coronavirus, for example, researchers compare the number of people in the vaccinated and placebo groups who receive Covid-19. The actual effectiveness of a vaccine may be different from its effectiveness in a trial.
- Phase 1, 2 and 3 trials: Clinical trials generally take place in three stages. Phase 1 trials typically involve a few dozen people and are designed to observe whether a vaccine or drug is safe. Phase 2 trials, involving hundreds of people, allow researchers to try different doses and gather more measurements of the vaccine’s effects on the immune system. Phase 3 trials, involving thousands or tens of thousands of volunteers, determine the safety and effectiveness of the vaccine or drug while waiting to see how many people are protected against the disease they are supposed to be fighting for.
- Placebo: A substance with no therapeutic effect, often used in a clinical trial. To see if a vaccine can prevent Covid-19, for example, researchers can inject half of their volunteers with the vaccine, while the other half are given a saltwater placebo. They can then compare the number of people in each group infected.
- Post-market surveillance: The follow-up that takes place after the approval of a vaccine or drug and is regularly prescribed by doctors. This monitoring usually confirms that the treatment is safe. On rare occasions, it detects side effects in certain groups of people that were missed in clinical trials.
- Preclinical research: Studies that take place before the start of a clinical trial, usually involving experiments where a treatment is tested in cells or in animals.
- Viral vector vaccines: A type of vaccine that uses a harmless virus to introduce immune system boosting ingredients into the human body. Viral vectors are used in several experimental Covid-19 vaccines, including those developed by AstraZeneca and Johnson & Johnson. Both companies use a cold virus called adenovirus as a vector. The adenovirus carries coronavirus genes.
- Test protocol: A series of procedures to be performed during a clinical trial.
Food and Drug Administration spokesperson Stephanie Caccomo declined to say whether the dosing error would hurt the vaccine’s chances of being cleared. The FDA has said it expects the vaccines to be at least 50% effective in preventing or reducing the severity of the disease, a bar the vaccine appears to have eliminated even in the group that received both doses. complete.
AstraZeneca shares have fallen around 5% this week, while broader stock indexes have hit record highs. Investors appear to be disappointed with the murky results, especially compared to the much clearer data released by two of AstraZeneca’s main rivals in the coronavirus vaccine race.