Findings of a recent Stanford University study seem to show that the U.S. remains a far cry from achieving herd immunity to the coronavirus. It suggests that just over 9% of Americans had developed antibodies to the virus as of the end of July.
Herd immunity occurs when enough of a population has developed protection against a virus so that it can no longer spread efficiently. In the case of COVID-19, public health experts have said that approximately 70% of the population needs to develop antibodies to the virus – either by becoming infected or by receiving a vaccination – to achieve herd immunity.
The Stanford study examined blood plasma samples from more than 28,000 randomly selected people who received dialysis treatments in 46 states this July. Although they tended to be older and included a higher percentage of men than women, the researchers considered the group to be an accurate barometer of COVID-19 prevalence across the nation.
When the researchers adjusted their results for the general population, they concluded that an estimated 9.3% of the U.S. population had developed antibodies to the coronavirus by mid-summer. Perhaps just as interestingly, their analysis revealed that relatively few people found to have antibodies – just 9.2% – had actually received a diagnosis of COVID-19.
The study also found that the percentage of people with antibodies differed greatly from region to region. For example, it was much higher in hard-hit northeastern states, where an estimated 27.2% of the national dialysis population tested positive for antibodies. On the other hand, an estimated 3.5% of those in western states were positive. Those living in the most densely populated urban areas were 10 times more likely to have antibodies.
“This research clearly confirms that despite high rates of COVID-19 in the (U.S.), the number of people with antibodies is still low, and we haven’t come close to achieving herd immunity,” said study co-author Dr. Julie Parsonnet. “Until an effective vaccine is approved, we need to make sure our more vulnerable populations are reached with prevention measures.”