Delta variant creates new challenges for achieving herd immunity, experts say

Earlier in the pandemic, before the delta variant came around, medical experts said the United States could achieve herd immunity if 60% to 75% of the population was vaccinated or had antibodies.

"Now, with delta, it's about 80 to 90 percent, so we need to have a lot more people immune to the virus before we can see this kind of, more global inhibition of transmission," said Dr. Michael Teng, an immunologist and associate professor of medicine at the University of South Florida.

For someone who becomes infected with the delta variant who is not vaccinated, they could be highly contagious for about a week, Dr. Teng said.  But if you have the shot(s), you can still get infected but the severity of infection is reduced and the vaccine shortens the amount of time someone is contagious.

"If you're vaccinated and you're infected with delta, it's probably like three days, so there's a significant difference in how infectious you are as a person if you've been vaccinated versus unvaccinated. So that short-term infectiousness will decrease the transmission because you won't come into contact with that many people," Dr. Teng said.

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In order to reach herd immunity, Dr. Teng says a lot more eligible Americans need to get the COVID-19 vaccine.