AURORA, Colo. (CBS4) – Study of a promising COVID-19 vaccine by Novavax is continuing in the U.S. and Mexico. Now, clinical trial participants, including me, are rolling up our sleeves for a third shot and then, three weeks later, a fourth.

“Today, Novavax began what we call a blinded crossover,” said Dr. Thomas Campbell, lead investigator at the study site at UCHealth, one of 115 sites.

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That means the participants who originally got two shots of the vaccine will get two shots of placebo and those who got two shots of placebo will get two shots of vaccine.

“Everybody who is still in the study will know they’ve been vaccinated, but they won’t know when they got the vaccine,” explained Campbell.

Results from a United Kingdom study showed the Novavax vaccine was 96% effective against the original virus, 86% against the UK variant and 60% against the South African variant. Thirty-thousand people enrolled in the US/Mexico clinical trial.

Ninety of 285 volunteers at the UCHealth site in Aurora opted to be unblinded when they became eligible for a vaccine already on the market. The rest of us stayed blinded.

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“That will provide an additional opportunity to assess safety and durability of the vaccine,” said Campbell.

Campbell believes Novavax could release data and apply to the FDA for emergency use authorization (EUA) in late May. The Novavax vaccine approach is a tried and true method. It works by teaching the immune system to make antibodies to a lab-made version of the SARS-CoV-2 spike protein.

It is made much like the HPV and HEP B vaccines.

It doesn’t need to be deep frozen like the Pfizer vaccine.

“We just need as many safe and effective vaccines as we can get,” said Campbell.