Surveys have shown that the public trust in a Covid-19 vaccine remains on shaky ground
By Denise Chow
The first experimental coronavirus vaccines could be available by the end of the year, and while that’s welcome news for public health officials, surveys have shown that people’s trust in a Covid-19 vaccine remains on shaky ground.
A Gallup poll in November found that 58 percent of Americans say they would get a Covid-19 vaccine, up from a low of 50 percent in September. But there are still worries that the speed of developing and testing the vaccines may have compromised their scientific integrity.
Fauci is confident of the process, but what are scientists paying attention to when it comes to vaccine safety?
Trial size and design: Larger is better
Clinical trials are typically made up of three main phases, but not all vaccine trials are designed the same way. In general, larger trials are ideal, with participants across age groups and ethnicities, because they will provide researchers with more data about how a potential vaccine performs in different populations. Large trials are also more likely to pick up on any serious safety issues, according to Daniel Salmon, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health.
“The issue you want to think about is size, because it tells you how rare of an event you can detect,” said Salmon, who served as director of vaccine safety in the Department of Health and Human Services’ National Vaccine Program Office during the 2009 H1N1 swine flu pandemic.
The vaccine candidates in late-stage clinical trials in the United States — including the vaccines developed by Pfizer and Moderna — are considered very large because they include an average of 30,000 volunteers each. Both companies also recruited a diverse group of participants and included people of different ages and medical backgrounds. Moderna’s trial, for instance, enrolled 5,000 people with high-risk chronic diseases.
How well it protects
Pfizer and its German partner, BioNTech, released additional data Wednesday following the completion of their Phase 3 trial. The companies announced that their vaccine was 95 percent effective at preventing symptomatic Covid-19, an improvement over the 90 percent efficacy that Pfizer reported in a preliminary analysis a week earlier.
Moderna said Monday that early results of its Phase 3 trial show that the company’s experimental vaccine is 94.5 percent effective at reducing infection.
Experts say these results are encouraging, but more data is needed to know what they mean.
“Ninety-five percent effective is amazing, but the question is: effective at what?” Salmon said. “Does it prevent contracting the disease altogether? Does it prevent clinical disease? Does it prevent serious disease? And does it prevent transmissibility? Those are different questions.”
Should we withhold the vaccine from the population for two years because we want perfect data?
Food and Drug Administration Commissioner Dr. Stephen Hahn said the promising results so far offer hope that these vaccines could be “the equivalent of a medical home run,” but added that the agency will need to carefully assess the raw data from the trials.
“We don’t just look at a scientific paper or press release,” Hahn said Thursday during a Facebook Live interview with Dr. John Torres, NBC News senior medical correspondent.
Tracking side effects
The FDA requires that vaccine developers submit two months of follow-up safety data as part of the application for emergency use. This is a critical step to ensure that drugmakers can monitor trial participants for any serious safety issues after vaccination.
Typically, most side effects from vaccines appear within 60 days of receiving the shot, according to Dr. Grace Lee, a professor of pediatrics at the Stanford University School of Medicine. But it’s possible for rare issues to crop up later, which means the FDA will need to weigh the potential benefits over the known risks before granting emergency use authorization.