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DENVER (KDVR) — Is it possible the U.S. could reach herd immunity from COVID-19 by April?

Dr. Marty Makary of Johns Hopkins School of Medicine thinks so, and he wrote an op-ed in the Wall Street Journal.

Makary said the number of COVID cases has dramatically dropped in the last six weeks in part, he believes, due to vaccinations and in part due to natural immunity, which he says is more common than expected.

But other doctors aren’t as confident.

“I’m, I guess, a little more skeptical,” said Dr. Michelle Barron, the medical director of infection prevention at UCHealth.

Barron believes we will hit herd immunity closer to fall. She says researchers still don’t know how long immunity from infection will last, and there are variants to consider.

“Some of the studies out of South Africa suggested that, even if you had prior infection, you could still get infection with one of these new variants,” Barron said.

So why have the number of COVID cases dropped?

Dr. Eric Lung, the chief medical officer at Sky Ridge Medical Center, says he believes it is due to mask wearing, social distancing and hand washing.

“People are being wise about their contact,” he said. “Only a small amount of the population has been vaccinated.”

Lung says 70% to 90% of the country will need to be immune to hit herd immunity.

Right now, he believes vaccine manufacturing and distribution, plus people’s attitudes about the vaccine, could slow that process down.

But Dr. James Neid, the director of infection prevention at the Medical Center of Aurora, says if people continue with precautions and the vaccine roll out continues at this pace, he is hopeful to see some changes by the end of April, even if it’s not full herd immunity.

“At this rate, we’re going to be over 50% of the country that will either be infected or vaccinated, and that is starting to tip the scales toward opening up a little bit more, with safety surrounding that. But I don’t want to get too confident. We are still 6 to 10 weeks from that prediction,” Neid said.