Some companies are developing vaccines that will likely be easier to mass produce than Pfizer’s and Moderna’s, but they have paused their clinical trials for safety reasons.
AstraZeneca said it had manufactured enough of its vaccine to meet its promise of hundreds of millions of doses by January, but a six-week pause in its trial meant that it probably wouldn’t get data on the performance of its vaccine in time to win federal authorization for its use this year.
The company’s chief executive, Pascal Soriot, recently told investors that it would fill the vials once it had a clearer picture of when the vaccine, which requires two doses, could be approved. “As soon as you turn this vaccine into vials, the shelf life starts ticking,” he said.
The vaccine maker Novavax — which had robust results in early studies and said it could supply the world with more than two billion doses next year — had to delay a large clinical trial by at least a month in part because of problems manufacturing tens of thousands of doses needed for the trial. The company has a $1.6 billion deal with the federal government to develop and manufacture its vaccine, which requires two doses.
In a statement, a Novavax spokeswoman said, “There are a number of things that can slow a trial start from the ideal plan, and it’s an immensely complex undertaking.” She said the company was ramping up manufacturing around the world.
Johnson & Johnson, which started its clinical trial in September, later than its competitors, has said it is on track to manufacture 100 million doses of its single-dose vaccine by March and a billion by the end of next year. Its executives have said they do not expect trial results until early next year.
Confused by the all technical terms used to describe how vaccines work and are investigated? Let us help:
- Adverse event: A health problem that crops up in volunteers in a clinical trial of a vaccine or a drug. An adverse event isn’t 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 the coronavirus and stop it from infecting cells.
- Approval, licensure and emergency use authorization: Drugs, vaccines and medical devices cannot be sold in the United States without gaining approval from the Food and Drug Administration, also known as licensure. After a company submits the results of clinical trials to the F.D.A. for consideration, the agency decides whether the product is safe and effective, a process that generally takes many months. If the country is facing an emergency — like a pandemic — a company may apply instead for an emergency use authorization, which can be granted considerably faster.
- Background rate: How often a health problem, known as an adverse event, arises in the general population. To determine if a vaccine or a drug is safe, researchers compare the rate of adverse events in a trial to the background rate.
- Efficacy: A measurement of how effective a treatment was in a clinical trial. To test a coronavirus vaccine, for instance, researchers compare how many people in the vaccinated and placebo groups get Covid-19. The real-world effectiveness of a vaccine may turn out to be different from its efficacy in a trial.
- Phase 1, 2, and 3 trials: Clinical trials typically take place in three stages. Phase 1 trials usually 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 out different doses and gather more measurements about the vaccine’s effects on the immune system. Phase 3 trials, involving thousands or tens of thousands of volunteers, determine the safety and efficacy of the vaccine or drug by waiting to see how many people are protected from the disease it’s designed to fight.
- Placebo: A substance that has no therapeutic effect, often used in a clinical trial. To see if a vaccine can prevent Covid-19, for example, researchers may inject the vaccine into half of their volunteers, while the other half get a placebo of salt water. They can then compare how many people in each group get infected.
- Post-market surveillance: The monitoring that takes place after a vaccine or drug has been approved and is regularly prescribed by doctors. This surveillance typically confirms that the treatment is safe. On rare occasions, it detects side effects in certain groups of people that were missed during clinical trials.
- Preclinical research: Studies that take place before the start of a clinical trial, typically involving experiments where a treatment is tested on cells or in animals.
- Viral vector vaccines: A type of vaccine that uses a harmless virus to chauffeur immune-system-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 of these companies are using a common cold virus called an adenovirus as their vector. The adenovirus carries coronavirus genes.
- Trial protocol: A series of procedures to be carried out during a clinical trial.
Still, even seasoned manufacturers can experience setbacks. Mr. Yadav, the supply chain expert, pointed to a shortage of flu vaccines in 2004, when a major manufacturer announced that 50 million doses, or half of the national supply for the United States, had been contaminated. “Those are risks that we will have to keep in mind,” he said.