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According to documents released this week, Pfizer researchers plan to tell all study participants who ask if they received a placebo or the vaccine. If this volunteer belongs to a group eligible to receive the vaccine based on their condition’s prioritization schedule, the company will provide the vaccine as part of the study. In other words, the volunteer will not have to give up to get the vaccine active. This means the company will be able to follow vaccinated participants for up to 18 months to monitor them for any side effects. As an added incentive, Pfizer is also offering to provide vaccines to anyone on the placebo arm who completes 6 months of follow-up, regardless of where they are in their state’s queue for priority to be vaccinated. .
That won’t be enough, according to Steven Goodman, epidemiologist and associate dean of clinical and translational research at Stanford University School of Medicine. At Thursday’s meeting, Goodman addressed the ethical issues that swirl around a potential EUA for the Pfizer vaccine. Echoing the case presented last week by bioethicists at the National Institutes of Health in Science, he pointed out how continued placebo-controlled vaccine trials might be ethically justified, as there is still so much to learn from them about who the vaccine works best and what its limitations are. He also pointed out that, even without the vaccine, participants have ways to reduce their risk of catching Covid – masks, social distancing, the complete suite of Swiss cheeses. The problem with continuing studies as planned, with a placebo group, is not ethics, Goodman said, but rather feasibility.
To that end, he offered a potential compromise. In the immediate future, manufacturers like Pfizer may switch to a trial design called a “double crossover”. Instead of telling participants which study arm they are enrolled in, investigators could offer each another set of vaccines when they become eligible for the vaccine, based on national and local priority schedules. This time, anyone in the placebo group would receive the vaccine, and those in the vaccine group would receive a placebo. Everyone would be vaccinated, but none of the subjects would know who was originally in the placebo group. This would protect some of the blindness of the study, while removing the incentive for participants to drop out. While this design might mean that it would take longer to get answers to questions about long-term sustainability and safety, it would at least preserve the ability to answer them.
Later, as more vaccines become available through the EUA, Goodman proposed that the trials should evolve into a head-to-head model, comparing vaccines to each other without a true placebo arm, similar the types of tests that resulted the very first treatment for Ebola last year.
Pfizer executives did not commit to making any changes to its proposed plan at Thursday’s meeting. William Gruber, the company’s senior vice president of clinical vaccine research and development, said it would be one of the things Pfizer will discuss with the FDA and CDC in the days and weeks to come. The company estimates that healthcare workers, who will be the first in line for a vaccine made available through an EUA, represent 20% of its Phase 3 study cohort. Gruber said losing this group would not completely derail the study. Where it could become risky is if CDC officials quickly increase the number of groups they recommend immunizing, he said. “We want to be conscientious in providing vaccines to eligible people.” Gruber suggested it would be easier with Pfizer’s current plan. He expressed his skepticism about the possibility of achieving a double crossover. “The logistics are not trivial,” he said.
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