RALEIGH, N.C. (WNCN) – A clinical trial studying a third dose of the Pfizer COVID-19 vaccine is underway at Wake Research in Raleigh.

“The idea here is to see what the immune response will be and how it compares to just two doses,” said Dr. Matthew Hong with Wake Research.

Half of the people in the study will receive the same Pfizer shot as doses one and two. The other half will get a placebo. Researchers will use the same people who participated in the original Pfizer trials so they can truly analyze the impact of the third dose.

“You’ll be looking at exactly the same immune system in every single case,” Hong said.

Hong said Pfizer’s data in a very small study showed antibody levels jumped significantly after a third dose, even against the delta variant, but the trial will show whether it works in a larger group of people in a real-world scenario.

“Are you actually seeing fewer sick people in the booster group rather than the people who received two shots?” Hong asked.

That’s the question the trial seeks to answer. It will help determine whether a third dose is needed to prevent breakthrough cases.

So far, Hong said he has not seen a significant number of breakthrough cases involving the people in the original clinical trial who received two doses. He said antibody levels six months after the third dose will give researchers a good comparison between two doses and three, but they’ll collect safety data and look at how many people are getting sick throughout the trial.

If COVID-19 keeps surging and people are getting breakthrough cases, he said it’s possible federal regulators may authorize booster shots sooner if they determine they are safe, effective, and necessary.

“It’s a day-to-day, week-to-week thing,” Hong said.

While the current booster trial is only for people who already participated in the Pfizer trial, Wake Research is conducting additional COVID-19 vaccine and treatment trials.