About 40 percent of infected persons show no symptoms but may transmit disease
Researchers with the Centers for Disease Control and Prevention (CDC) have just published the results of blood tests seeking antibodies for COVID-19. This seroprevalence study in the Journal of the American Medical Association (JAMA) scanned blood samples taken from more than 16,000 people from 10 areas around the U. S. during varying time periods in April and May. The samples are not random but were gathered from patients who were visiting their physicians or hospitals for treatments and checkups. Based on these test results, the researchers conclude that at most of the sampled areas « it is likely that greater than 10 times more [coronavirus] infections occurred than the number of reported COVID-19 cases. » In fact, they estimated that the ratio of undetected infections to reported cases ranged from being six times greater in Connecticut, to 24 times greater in Missouri. The researchers caution that « extrapolating these estimates to make assumptions about population immunity should not be done until more is known » about how much long-term protection against re-infection antibodies may provide. They further note that their findings « may reflect persons who had mild or no illness or who did not seek medical care or undergo testing but who still may have contributed to ongoing virus transmission in the population. » The CDC recently estimated that about 40 percent of people infected with the virus that is responsible for COVID-19 exhibit no symptoms and the chance of transmission from such people is around 75 percent.
