SIOUX FALLS, S.D. (KELO) — Nearly one of three South Dakotans have been previously infected with COVID-19, an on-going study by the National Institutes of Health shows.
According to the COVID-19 SeroHub, a study that uses blood tests to identify the proportion of people in the population who possess antibodies to COVID-19, South Dakota was at 31% by May 2021. The confidence interval is listed as low as 21% or as high as 41% of South Dakota’s general population has been previously infected.
Dr. Paul Carson, an infectious disease specialist and professor of public health at North Dakota State University, referenced the COVID-19 SeroHub study during a North Dakota Department of Health webinar discussing the Delta variant.
What percent of people have been previously infected with COVID-19? That’s the magic question and Carson said officials are trying to conduct a study in North Dakota to find out how many people have been previously infected with the virus.
Carson said the prior infection data collection comes from the National Institutes of Health in collaboration with health care systems that draw blood across the country. The blood samples are all anonymous and the data showed 22% of the U.S. population has antibodies from prior infection through May 2021.
“This is antibodies from the virus, not to the vaccine and there’s a way to distinguish that,” Carson said during the webinar. “That’s not homogeneous, it’s kind of spotty.”
The data is broken down by state and Carson entered it into a map, which showed South Dakota had 31% of the population previously infected. Minnesota was listed at 12% and Iowa at 15%. North Dakota was not included in the survey, but Carson estimated North Dakota would be close to South Dakota.
“We ran sort of neck-to-neck with them with hospitalizations and deaths,” Carson said. “They exceeded us by a bit.”
By natural infection, Carson says North Dakota is nowhere close to herd immunity. He said it is difficult to calculate what percent of people with prior infection also became part of the fully vaccinated population.
“I think, at best, we’re maybe looking at 50, 60, 60-plus percent of us having some form of immunity either through vaccination or prior infection,” Carson said. “That leaves a lot of people still out there susceptible to the virus.”
The latest total case count from the South Dakota Department of Health is 125,216, which is roughly 15% of South Dakota’s population of 886,667, as reported by the 2020 U.S. Census.
Carson said anyone who has previously been infected with COVID-19 has some level of protection from the virus, but it is unclear how well natural immunity protects people.
“That’s a fair question,” Carson said.
He referenced a study of the Cleveland Clinic, where both vaccinated healthcare workers and previously infected but unvaccinated healthcare workers had similar very low infection rates through five months. The study was conducted before the Delta variant became the dominant strain.
A larger study in Denmark, Carson referenced showed natural infection protection rates were above 80% for people aged newborn to 64. For age 65 and above, natural infection protection was at 47%.
‘Clearly an epidemic of the unvaccinated’
Joining Molly Howell, immunization director for the North Dakota Department of Health, Carson started his presentation saying how the World Health Organization has called the Delta variant the “fastest and the fittest.”
The Delta variant is 65% more contagious than the Alpha variant, which Carson said makes the Delta variant twice as contagious as the original coronavirus strain.
He used the example of India, where new studies show 67% of residents in India now have antibodies for COVID-19.
“That’s a huge number,” Carson said. “It rapidly swept through and apparently caused infection in almost two-thirds of the population of India in a very short period of time.”
Right now, Carson said more than 90% of the samples sequenced by the CDC in the region which includes South Dakota and North Dakota are coming up as the Delta variant.
The combination of the more contagious delta variant, hot summer weather forcing more indoor gatherings and low vaccination rates are likely fueling the rise in cases for southern states like Florida, Louisiana, Mississippi and Arkansas, Carson said.
“Like we saw last summer, during the summer the southern states were very, very hot,” Carson said. “In the south, when it gets very, very hot, they tend to go indoors more. Indoor congregating and air conditioned air is better at spreading the virus.”
Arkansas, Louisiana and Mississippi are all below 37% of the total population fully vaccinated. Carson compared those fully vaccinated rates to North Dakota (39.7%), South Dakota (46.5%) and Minnesota (53.3%).
South Dakota’s Department of Health is reporting 53% of the state’s eligible population (12-years-old and older) is fully vaccinated.
“Right now, it’s clearly an epidemic of the unvaccinated,” Carson said.