Kevin J. Beaty/Denverite Medical assistant Yasmin Tellez preps a Modetna COVID-19 vaccination at Globeville's Clinica Tepeyac. Jan. 26, 2021. Experts say vaccination efforts will have to quicken to stay ahead of viral mutations. Behind the recent drop in Colorado's COVID-19 case numbers is a persistent growth in the number of viral variant cases detected that have the potential to mess with everything from in-person school to the re-opening of the economy. The variants have turned the effort to vaccinate Coloradans into a race to develop immunity before the virus has morphed itself significantly enough to evade the vaccines. “I'm nervous about the variants,” said Dr. Anuj Mehta, a pulmonologist with National Jewish Health and Denver Health, who serves on the Governor’s Expert Emergency Epidemic Response Committee. “I'm just concerned that the variants could potentially fuel another surge.”