By Dr. Mallika Marshall

BOSTON (CBS) – There’s concern that the Delta variant could make it even harder to achieve herd immunity.

Herd immunity is achieved when enough people are immune, the coronavirus has few places to go, and the entire population is protected.

But the more contagious the disease, the greater the proportion of people who need to be immune to prevent spread.

With the original coronavirus, it was estimated that about 67% of the population would need to be vaccinated to reach herd immunity.

But because the Delta variant spreads so easily, some believe that percentage is now closer to 80%, perhaps even as high as 90%.

Dr. Mallika Marshall