16 million Americans undiagnosed with Covid during first wave, antibody analysis suggests

A study has suggested that cases of Covid-19 were actually five times the rate of all diagnosed infections during the first wave in the United States.

Findings from the National Institutes of Health (NIH), which were released on Tuesday, shows that almost 17 million Americans were infected with Covid in the first half of 2020.

Figures at the time revealed that 3 million Americans were infected with Covid-19 from January to July 2020, at a rate five times fewer than the NIH’s new findings.

Matthew J Memoli, from the NIH, told an ABC affiliate that counting asymptomatic infections was a “hallmark” of Covid, as all of the participants had been “undiagnosed” with the virus.

“While counting the numbers of symptomatic people in the United States is essential to contend with the impact of the pandemic and public health response, gaining a full appreciation of the Covid-19 prevalence requires counting the people who are undiagnosed,” said Mr Memoli.

The NIH’s findings suggest 5 per cent of the US population contracted Covid-19 in the first wave, from January to July 2020.

“The estimate of Covid-19 cases in the United States in mid-July 2020, 3 million in a population of 330 million, should be revised upwards by almost 20 million when the percent of asymptomatic positive results is included,” said senior co-author of the study, Kaitlyn Sadtler.

“This wide gap between the known cases at the time and these asymptomatic infections has implications not only for retrospectively understanding this pandemic, but future pandemic preparedness.”

According to the NIH, who analysed blood samples of “undiagnosed” Americans for signs of Covid antibodies, the highest rates of infection were among women, those aged between 18 and 44, and residents of urban areas.

Black Americans were also found to have Covid antibodies at a rate 5.7 times that of white Americans, with 14.2 per cent of the former showing signs of infection, compared to 2.5 per cent for the latter.

More than 8,000 volunteers took part in the study, who were chosen from an initial pool of 460,000 to best recreate the whole US population.

“Our findings have implications for understanding SARS-CoV-2 spread … and prevalence in different communities and could have a potential impact on decisions involved in vaccine rollout,” the authors of the NIH study concluded.