• In Arkansas, which is seeing the third-worst Covid outbreak in the country based on daily new cases per capita, vaccinations have nearly tripled.
• Mississippi, experiencing the fourth-worst outbreak in the country, saw a 178% increase by Aug. 4 in first doses administered.
• Louisiana is experiencing the worst outbreak of new Covid cases per capita in the country and record hospitalizations.
• Even with the recent surge in vaccinations, Louisiana still ranks fifth-lowest in the country in residents who are fully vaccinated, at 37.2%.

More and more people who were once vaccine hesitant in several Southern states are now getting their first shots as the delta Covid variant rips through areas of the U.S. with low immunization rates.

In Arkansas, Mississippi, Louisiana and Alabama, the seven-day average of daily reported first doses has more than doubled since the start of July, Centers for Disease Control and Prevention data shows, as the outbreak has worsened nationwide.

Over that same time period, average daily case counts have grown from about 13,000 per day across the country to roughly 94,000 per day as of Aug. 4, according to data compiled by Johns Hopkins University, with the overwhelming majority of new infections among those who are unvaccinated.

"Clearly, Americans are seeing the impact of being unvaccinated and unprotected and they're responding by doing their part, rolling up their sleeve and getting vaccinated," White House Covid czar Jeff Zients told reporters Thursday.

In Arkansas, which is seeing the third-worst outbreak in the country based on daily new cases per capita, vaccinations have nearly tripled. On July 1, the state was administering a seven-day average of 2,893 first doses in arms, representing new people getting their first shots, according to a CNBC analysis of CDC data. By Aug. 4, that number shot up to a seven-day average of 8,585 first doses administered per day.

Mississippi, experiencing the fourth-worst outbreak in the country, saw a 178% increase by Aug. 4 in first doses administered since the start of July. Louisiana had a 128% increase, and Alabama, hosting the fifth-worst outbreak nationwide, saw a 109% rise.

Louisiana is experiencing the worst outbreak of new Covid cases per capita in the country and record hospitalizations after the delta variant took aim at the state's mostly unvaccinated population.

The state's governor has reimplemented a mask mandate until at least Sept. 1 in an effort to slow down transmission. Even with the recent surge in vaccinations, Louisiana still ranks fifth-lowest in the country in residents who are fully vaccinated, at 37.2%.

"Louisiana's COVID-19 vaccination rate is not where we need it to be, and this in combination with the delta variant have resulted in the perfect storm we are seeing right now," Mindy Faciane, public information officer at Louisiana Department of Health told CNBC.

Behind Louisiana is Arkansas at 37% of residents fully vaccinated, Wyoming at 36.7%, Mississippi at 34.8% and Alabama at 34.6%, according to CDC data.

Covid cases with severe outcomes are also on the rise, according to U.S. officials. The seven-day average of daily hospitalizations is up 41% from a week ago with the average daily death toll up 39%, CDC Director Dr. Rochelle Walensky said Thursday.

Studies have shown that the delta variant is much more transmissible than the original Covid strain and, unlike the original, requires two vaccine doses for the body to have a fighting chance at preventing infection and severe symptoms.

"Even if somebody decided today that they wanted to get the vaccine, it's going to take some time before their body and immune system is educated to be able to deal with it," Gigi Gronvall, an immunologist and senior scholar at Johns Hopkins Center for Health Security, told CNBC. "You want to make sure you don't get exposed before your body can have a chance to shut that virus down." 

Still, residents in hard-hit states initiating vaccination will help slow the spread of the virus sooner rather than later and could prevent hospitalizations and deaths in the future.

"People are seeing how this is affecting their communities and they are actively changing their minds to get the vaccine," Faciane said. "Our vaccination rate is through the roof right now."

Patients of varying ages hospitalized with Covid in states such as Missouri, Florida, Arkansas and Louisiana are expressing regret that they initially declined to get the shot and are pleading with their communities to get vaccinated.

Overall, the U.S. is reporting an average of about 677,000 daily vaccinations over the past week as of Aug. 4, up 11% from one week ago.

The number of first vaccine doses is climbing more sharply than the overall rate. An average of about 446,000 first doses were administered every day over the past seven days as of Wednesday, according to the CDC, up 17% from the week prior.