The first vaccine that proves to safely protect people against Covid-19 disease will be a breakthrough moment but is unlikely to be the sole answer to curbing the coronavirus pandemic.
Instead, health experts say it’s increasingly likely that several vaccines could pass muster in clinical trials and become available in phases over a period of weeks and months.
A multiplicity of experimental vaccines provides bench strength in the event of more potential delays like the one AstraZeneca PLC encountered earlier this week, after a volunteer in a U.K. vaccine trial developed an unexplained illness, leading the company to pause studies to review safety data.
Multiple vaccines would have implications for supply and distribution plans. If testing is successful, it’s possible that rollouts of vaccine doses could start as soon as this coming fall and stretch into 2021 and beyond.
“I think the general public maybe has the wrong impression that there will be a winner and only one winner and everybody else will be a loser, ” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in an interview. “That’s not the case at all. I think it’s quite conceivable, if not likely, that you’re going to have multiple candidates that’ll get over the finish line that will actually be good enough to be approved for production and use.”
Not all vaccines in testing are likely to succeed but several have shown promise in small, early-stage human studies. At least two vaccines are now in large, late-stage clinical trials in the U.S., including one co-developed by Moderna Inc. with the National Institutes of Health and another from Pfizer Inc. and BioNTech SE. A third, from AstraZeneca and the University of Oxford, is on hold pending the safety review.
The large trials are designed to generate enough evidence about safety and efficacy to support a government decision on whether to clear them for widespread use. Companies have said interim results of the studies could be available starting in the fall, possibly as soon as October, and if positive, could trigger U.S. authorization of emergency use of the shots.
Novavax Inc. and Johnson & Johnson are planning to begin large trials of their experimental vaccines this month, with potential availability of initial doses by year-end or in early 2021. Vaccines developed in China and Russia also are in advanced stages of testing and have shown promise in studies so far.
U.S. officials have signaled there could be at least two vaccines available by the end of this year. The Centers for Disease Control and Prevention sent documents last week to state officials that lay out various scenarios, including availability of a limited number of doses of two vaccines by the end of October with more doses by the end of the year.
The CDC document doesn’t name the two vaccines that could become available but describes characteristics that match those of the vaccines from Pfizer and Moderna.
Experts say multiple vaccines will be needed because no single company can make enough for the whole world. Several companies have signed contracts with the federal government to supply at least 100 million doses of each vaccine in the U.S., and are planning to produce larger global supplies.
“We need multiple winners to have enough vaccines,” said Dr. Mark Mulligan, director of the NYU Langone Vaccine Center in New York, which is helping to run a trial of the Covid-19 vaccine co-developed by Pfizer and BioNTech.
Not everyone will be able to get vaccinated right away because initial supplies will be limited — perhaps 10 million to 15 million in the U.S., according to a draft report released this week by the National Academy of Medicine.
There’s likely to be a staggered rollout of which people can get the shots. Last week, a National Academy of Medicine committee proposed an allocation plan for the U.S. that would give the first vaccine doses to front-line health-care workers in hospitals and nursing homes who are at risk of infection.
These would be followed in phases by other groups such as older adults in nursing homes, people with health conditions that increase risk of more-severe Covid-19, and workers in essential industries, before reaching the general population.
Having multiple vaccines could serve another purpose beyond shoring up supply. Each vaccine may turn out to have different safety and efficacy profiles, or other traits that could make it more or less useful in certain groups, such as the elderly.
“There are going to be multiple vaccines of different degrees of effectiveness, and different degrees of effectiveness in a range of populations,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and part of a group trying to develop a low-cost Covid-19 vaccine for developing countries. He says it’s possible there will be four to five successful vaccines within the next year.
Some vaccines could prevent coronavirus infections, which would help reduce transmission of the virus, he said; others could reduce the severity of Covid-19 disease but not prevent infections.
Any such differences would have to be borne out by the results of the large Phase 3 trials, however, because the earlier studies didn’t test whether the vaccines prevented infections or reduced disease.
Logistical traits could make one vaccine more suitable for certain groups than others. For example, the two leading gene-based vaccines, from Pfizer and Moderna, must be stored and shipped at low temperatures, which could make them more suitable for vaccinating health-care workers at hospitals or other facilities that have the necessary storage equipment.
Having multiple vaccines could, however, add to the complexity of waging a successful vaccination campaign.
Several vaccines require two doses, so providers would have to track who gets which vaccine, and set up reminders to call them back for the second dose. Health experts say there’s no evidence yet that two different vaccines could be given effectively to the same person.
“It’s going to add to the complexity on the ground, to those people who are doing the vaccination,” said Dr. Eric Toner, senior scholar with the Johns Hopkins Center for Health Security. “I don’t think they can rely on patients to know which vaccine they received or remember a month later.”
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