The US has administered almost 330 million vaccine doses, but the debate is growing about whether the country can really relax with the spread of the Delta variant.
Despite the number of vaccinations, there are massive gaps in some areas. Less than 50% of adults in Alabama, Mississippi, and Louisiana have received a dose.
Dr Rachel Levine, assistant secretary at the US Department of Health and Human Services, said: "We don’t exactly know what the herd immunity percentage would be for Covid-19. It would be different for the Delta variant, and higher, because it is more transmissible"
Most ominously, the highly transmissible delta variant is on the rise and represents a quarter of confirmed cases, posing a greater risk to pockets of unvaccinated communities than earlier strains of the virus.