Why did the researchers test two different doses?
It was a lucky mistake. Researchers in the UK had intended to give volunteers the full strength starting dose, but they made a mistake and accidentally gave it half strength, Reuters reported. After discovering the bug, the researchers gave each affected participant the full strength booster shot as planned about a month later.
Of the more than 23,000 participants whose results were reported Monday, fewer than 2,800 volunteers received the half-strength starting dose. That's a fairly small number of participants on which the spectacular efficacy results can be based – far fewer than in the studies by Pfizer and Moderna.
Is the AstraZeneca vaccine safe?
For years, Oxford researchers have tested their chimpanzee adenovirus vaccine, ChAdOx1, on a number of other diseases, including Ebola and Zika. Although none of these studies made it to the definitive, so-called Phase 3 studies, they did allow researchers to investigate the safety of the vaccine platform. The researchers did not find any serious side effects.
When the researchers adjusted ChAdOx1 for Covid-19, their early clinical studies also showed no side effects. However, in phase 3 studies, the test had to be interrupted twice if the volunteers developed neurological problems. The Food and Drug Administration did not directly link the vaccine to the problems, but when the agency allowed the trial to resume in the US, they advised the company to look out for signs of similar problems.
In their announcement on Monday, AstraZeneca and Oxford said no serious safety issues related to the vaccine have been confirmed.
What does the vaccine cost?
AstraZeneca's vaccine offers a number of advantages over other leading vaccine candidates: At $ 3 to $ 4 per dose, it is easier and cheaper to mass produce and store. This reflects the prices paid by governments like the United States, which ordered dozens or even hundreds of millions of doses of the vaccine. U.S. health officials have promised that Covid-19 vaccines will be available free of charge to any American who wants one.
The road to a coronavirus vaccine
Interesting facts about vaccines
Confused by all of the technical terms used to describe how vaccines work and study? Let us help:
- Adverse event: A health problem that occurs in volunteers in a clinical trial with a vaccine or drug. An adverse event is not always caused by the treatment tested in the study.
- Antibody: A protein produced by the immune system that can bind to a pathogen such as the coronavirus and prevent it from infecting cells.
- Approval, licensing and approval for emergency use: Medicines, vaccines and medical devices cannot be sold in the US for no profit approval by the Food and Drug Administration, also known as Licensing. After a company has submitted the results of clinical studies to the F.D.A. For testing purposes, the agency decides whether the product is safe and effective. This process usually takes many months. If the country faces an emergency – like a pandemic – a company can file an application instead Emergency approvalthat can be granted much faster.
- Background rate: How often does the general population experience a health problem called an Adverse Event? To determine whether a vaccine or drug is safe, the researchers compare the rate of adverse events in one study to the background rate.
- Effectiveness: A measure of the effectiveness of a treatment in a clinical trial. For example, to test a coronavirus vaccine, the researchers compare how many people in the vaccinated group and the placebo group receive Covid-19. The actual effectiveness of a vaccine may differ from its effectiveness in a study.
- Phases 1, 2 and 3 studies: Clinical trials typically take place in three stages. Phase 1 studies typically involve a few dozen people to determine whether a vaccine or drug is safe. In Phase 2 trials, involving hundreds of people, researchers can try different doses and take 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 by waiting to see how many people are protected from the disease it is supposed to be fighting.
- Placebo: A substance with no therapeutic effect that is widely used in clinical trials. For example, to see if a vaccine can prevent Covid-19, researchers can inject the vaccine into half of their volunteers while the other half are given a placebo with salt water. You can then compare how many people are infected in each group.
- Post-market surveillance: The surveillance that occurs after a vaccine or drug has been approved and regularly prescribed by doctors. This monitoring usually confirms that the treatment is safe. In rare cases, side effects are noted in certain groups of people that were overlooked during clinical trials.
- Preclinical Research: Studies that take place prior to the start of a clinical trial typically include experiments that test a treatment on cells or animals.
- Viral vector vaccines: A type of vaccine that uses a harmless virus to deliver immune-stimulating 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 that must be performed during a clinical trial.
Does this mean it will soon be available in the US?
There is still a long way to go.
It is not yet clear whether the results announced on Monday are sufficient for AstraZeneca to take the first formal step in the regulatory process: filing an application with the F.D.A. Obtaining emergency authorization to distribute his vaccine. AstraZeneca plans to begin half strength initial dose testing in its ongoing US study and seek guidance from the agency on how to proceed. The agency will likely advise the company to collect more data on its promising dosing schedule before making a formal application for approval, several vaccine experts said.