— Jack Murphy 🇺🇸 ⚔️ (@jackmurphylive) September 3, 2021
Survey: More than 80% of Americans 16 and older have immunity
More than 80% of Americans 16 and older have some level of immunity against the coronavirus, mostly through vaccination, a survey of blood donations indicates.
The survey, led by the CDC, also indicates that about twice as many people have been infected with the virus as have been officially counted. More than 39 million Americans have been diagnosed with coronavirus infection since the pandemic started in 2020.
The team, led by the CDC’s Dr. Jefferson Jones, set out to determine how close the US might be to some kind of herd immunity — although they do not claim to have any kind of handle on that yet.
They worked with 17 blood collection organizations working in all 50 states plus Washington, DC, and Puerto Rico to test blood covering 74% of the population. In the end, they tested about 1.4 million samples.
In July 2020, before any vaccine was available, 3.5% of samples carried antibodies to SARS-CoV-2, the virus that causes Covid-19. That rose to 11.5% by December, they reported in the medical journal JAMA. By May, 83.3% of samples had antibodies to the virus, most of them from vaccination.
And while in July 2020, blood surveillance indicated the US was only counting one infection out of every three true infections, that fell to one in two a year later.
This was all pre-Delta, the researchers caution. Plus, they didn’t measure the other part of the human response — one involving cells known as T-cells — and one that might induce broader immunity. But knowing who has antibodies can help inform public health efforts.
“Several large studies have shown that among individuals who are seropositive from prior SARS-CoV-2 infection, COVID-19 incidence is reduced by 80% to 95%, similar to vaccine efficacy estimates,” they noted.
“The study will continue until at least December 2021, and results will be made available on the CDC’s website,” they wrote.