WASHINGTON — The number of new cases of COVID-19 in the U.S. has more than doubled in the last two weeks, according to The New York Times’ COVID tracker, with the delta variant proving difficult to contain and a divide forming between those who are vaccinated and those who are not.


As of July 14, the seven-day average of daily cases in the country was 26,513, up from 12, 540 on June 30, with a notable hotspot emerging across Kansas, Oklahoma, Missouri, Arkansas, Louisiana and Mississippi.


These are states where vaccination rates are among the lowest in the U.S., with just 35 percent of people in Mississippi fully vaccinated, compared to 66.5 percent in Vermont, which has the highest vaccination rate in the country, according to the U.S. Centers for Disease Control and Prevention.


The effects of infections are also proving much more dangerous to the unvaccinated. While 50 percent of Americans have been fully vaccinated, Associated Press analysis of U.S. government data showed 99 percent of deaths and hospitalizations from COVID in the last month involved those who were unvaccinated.


The role of the delta variant in causing many of these infections is now widely acknowledged. It made up 57.6 percent of new infections in the U.S. between June 20 and July 3, according to U.S. Centers for Disease Control and Prevention.


Delta is defined by several mutations to its spike protein, including at position L452R. Several of these mutations make the body’s immune responses less effective and according to The Global Virus Network, its P681R mutation, directly beside the furin cleavage site, is key in enabling the virus to grip onto and invade human cells more effectively.