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Clinical trials for Pfizer, Moderna 'designed with very rigid requirements,' medical experts say

Health experts weigh in on what scientific data is appropriate to use to answer immunity duration questions.

CHARLOTTE, N.C. — Both Moderna and Pfizer COVID-19 vaccines have immunity that lasts for at least six months after completing a two-dose series. According to one of the reports, which was published in the New England Journal of Medicine, some of this information comes from phase three clinical trial data.

A WCNC Charlotte viewer reached out after this information was released, asking whether researchers could look at earlier trial participants to see if immunity lasts even longer:

Moderna started trials 3/16/20 One Year ago. Why can't they go to their Phase 1 trial people and see what level... they have after one year later?


Can researchers look back at phase one trials to see if vaccine immunity lasts longer than six months?


No. Doctors say looking back at earlier trials would not provide any conclusive evidence.

Dr. Ryan Shelton, with Tryon Medical Partners, headed up the Moderna clinical trials in Charlotte.

He states, "Phase 1 trials don't have enough enrollees to be conclusive ... but all trial participants are being monitored for the amount of immune protection they have.”

Shelton added that under normal circumstances, the phase three trial would have continued for another few years before the vaccine went out to the general public. However, because of the severity of the pandemic, the red tape was removed to ease rollout. Shelton assures no safety steps were skipped.

Dr. Meg Sullivan, the Medical Director with Mecklenburg County Public Health, agrees, it is likely not scientifically sound to look at that older data with smaller enrollments.

"I think the way clinical trials are designed, they’re designed with very rigid requirements. That’s how phase 3 trial is designed—to see long term," Sullivan said. "Phase 1 is designed to look immediately at immunity. Is there a level of response? And then look at safety. It’s a very small trial. It’s designed to look at different endpoints than that phase 3 clinical trial. That’s why the majority of our data comes from there.”

As we get further removed from the start of the phase three trials, we will likely gain more insights into how long the vaccine immunity truly lasts.

Have a relative or friend in another state and want to know when they can get vaccinated? Visit NBC News' Plan Your Vaccine site to find out about each state's vaccine rollout plan.


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