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The difficulty is, hospital admissions and deaths from COVID-19 are uncommon, and it would require a large population over a longer period to accumulate enough deaths to see a difference between the vaccine and placebo group, Kimmelman said.
The U.S. Food and Drug Administration has set a minimum target of 50 per cent efficacy for a COVID-19 vaccine, meaning a vaccine would have to be 50 per cent better than a placebo at preventing disease.
In an early-stage study, Moderna’s COVID-19 vaccine produced neutralizing antibodies in 45 healthy, 18- to 55-year-olds who received two vaccinations, 28 days apart, the company reported in the New England Journal of Medicine. Side effects — fatigue, chills, headache or muscle aches — occurred in more than half the participants.
Dr. Jacqueline Miller, head of Moderna’s infectious diseases development, told last week’s FDA advisory panel meeting that more than 25,000 people have received both doses of its study vaccine, or a placebo, and that the vaccine was designed to evaluate Americans “at the highest risk of severe COVID disease.” Forty-two per cent of study participants are older adults or people with heart disease, diabetes or other underlying conditions, Miller added.
AstraZeneca’s vaccine, developed with Oxford University, has produced an immune response in both the young and old, Reuters reported this week. Less clear is how well an antibody response translates into how well any vaccine can actually fend off COVID.
