Blaine County tested a sample of residents for COVID-19 antibodies in April as part of a study, and some of the initial results are in.
Of the nearly 1,000 Blaine County residents tested, 23% had COVID-19 antibodies. In Ketchum, it was 35%, one of the highest prevalence rates of which the researchers are aware.
“This confirms the area did have a much higher rate of infection than most of the rest of the country,” said Colleen McLaughlin, an epidemiologist at the Albany College of Pharmacy and Health Sciences, which ran the study alongside the Fred Hutchinson Cancer Research Center in Seattle.
Antibodies usually show whether someone has developed immunity to a virus. They also tell if the person had the virus in the past. Researchers aren’t yet sure if having antibodies to COVID-19 guarantees immunity.
At one point, Blaine County had one of the highest per-capita rates of COVID-19 in the country. More than 500 people have tested positive, but the case numbers have slowed substantially since mid-April. Now, the South Central Public Health District is only monitoring one individual with symptoms in the county.
Despite the high infection rate, the county is likely still far from what scientists would consider herd immunity, McLaughlin said.
About 2,500 Blaine County residents signed up online for the study and 917 people were selected in order to roughly match the age and gender makeup of each zip code, or city. And while McLaughlin said the sample is fairly representative of the county, the study results can’t yet be applied to the county population as a whole.
“Because they were volunteers, and it wasn’t a random sample, we can’t make any inference beyond the people who were tested yet,” she said.
For example, the county’s Latino population was underrepresented in the sample, so the scientists are working on statistical models to account for factors like that.
The epidemiologists are also looking into why some people in a household tested positive for COVID-19 antibodies when others tested negative, and how the county’s epidemiological curve matches up with their findings.
Find reporter Rachel Cohen on Twitter @racheld_cohen
Copyright 2020 Boise State Public Radio
Member support is what makes local COVID-19 reporting possible. Support this coverage here.
