Studies found that less than 10% of Americans had COVID by September

A large serum prevalence study conducted in the summer shows that by September, less than 1 in 10 Americans had evidence of previous coronavirus infection, Centers for Disease Control and Prevention. (CDC) researchers yesterday JAMA Internal Medicine.

In National serum prevalence surveyResearchers on the CDC’s COVID-19 response team are looking for the presence of detectable antibodies to SARS-CoV-2, people in 50 states, the District of Columbia, and Puerto Rico during the four periods from July to September. Serum samples were tested. (The virus that causes COVID-19.

Estimates in some states reached 23%, but overall serum prevalence over all four periods was detectable in less than 10% of Americans with SARS-CoV-2 antibody. I showed that.

However, an additional CDC study showed that 28% of healthcare professionals who were previously antibody-positive did not have enough antibodies to be positive after 60 days, weakening antibody protection. ..

Big differences between regions

Purpose of cross section JAMA A study testing the sera of 177,919 people was to understand how serum prevalence varies by region, gender, age group, and duration. Previous serum prevalence studies focused on hotspots such as New York and California, or high-risk populations, but by late September this study had SARS-CoV- by several Americans nationwide. The purpose was to estimate if you might have been infected with 2.

Every two weeks, researchers collect a convenient sample of serum from blood taken for regular screening of cholesterol and other problems and use a commercially available immunoglobulin G (IgG) assay for SARS-CoV. Serum was tested for the presence of -2 antibody. Samples were taken from July 27th to August 13th, August 10th to August 27th, August 20th to September 10th, and September 7th to September 24th. Serum prevalence was estimated by jurisdiction, gender, and age group (0-17, 18-49, 50). 64, 65 and above), and metropolitan / non-metropolitan status.

Overall, 177,919 residual serum specimens were collected during the four periods, of which 58.3% were women, 15% were children, 26.7% were 65 years or older, and 14.8% were non-metropolitan people.

Results over four periods showed that there was large variability in serum prevalence estimates between regions and metropolitan and non-metropolitan areas, generally reflecting a pandemic trajectory. Two states at the epicenter of the spring pandemic, New York and New Jersey, showed the highest serum prevalence during each test period. In New York, serum prevalence reached as high as 23% during the first test period.

In South Dakota, on the other hand, the seropositive rate was 0% during the second test period. Estimates for southern states, where infections began to surge in the summer, reached 13%. However, it was less than 10% in the Midwest and West.

There was no consistent difference between men and women, and serum prevalence in people aged 65 and over was generally lower than in adults aged 18-49.

In 49 jurisdictions with sufficient samples to estimate serum prevalence over all four test periods, in New York (6.3) and North Dakota (6.1), the highest percentage points from period 1 to period 4 A decrease was observed, with an increase of the largest percentage points. Observed in Georgia (6.2) and Minnesota (4.5).

“We found that most people in the United States did not have evidence of previous SARS-CoV-2 infection,” the author writes. “This is another large serum prevalence study conducted in the United States and a population-based study conducted during periods of high infection in the SARS-CoV-2 community in the United Kingdom, Spain and Geneva. Is consistent with. “

A long way from herd immunity

so Accompanying commentaryInfectious disease experts at the University of Southern California Medical Center in Los Angeles County, Loyola University in Chicago, and Johns Hopkins Medical College said the study used sera sent to the laboratory for routine testing, resulting in seropathies nationwide. It states that the rate level can be read more accurately. Not from a suspected patient with COVID-19.

And what those levels suggest is that herd immunity in the absence of vaccines is a long way off.

“A robust and well-designed serum prevalence study using residual serum samples from across the United States shows where the herd immunity to SARS-Cov-2 is, even if the COVID-19 pandemic has been rampant for a year. I found that I couldn’t even see it, “they write. .. “We hope that safe and effective vaccines will help avoid the consequences of naturally developing herd immunity to COVID-19, as is the case with many other respiratory viruses. I will. “

Modeling studies and extrapolation from other infectious diseases suggest that 60% to 80% of the population needs to be infected to reach herd immunity, according to the authors of the commentary notes.

Antibody decline

However, whether post-infection antibody levels, a phenomenon observed in SARS-CoV-2 infected individuals, may lead to serum prevalence studies that underestimate the incidence of COVID-19. I have a question.That possibility is highlighted in Another CDC study, Released today Weekly morbidity and mortality reports.

In this study, researchers from the IVY Network, a joint group of the CDC’s COVID-19 Response Team and the Centers for Disease Control and Prevention, conducted serum samples from expedient samples of front-line healthcare professionals in 13 hospitals from April 3 to 13. Was tested for SARS-CoV-2 antibody. Then, 60 days later, I retested some of them. Overall, 194 (6%) of the 3,248 healthcare workers had baseline-detectable antibodies.

However, at the time of retest, 146 of 156 (93.6%) healthcare workers who returned for follow-up had reduced antibody response and 44 of 156 (28.2%) experienced serum recovery. That is, the antibody level was below the positive threshold. Participants with a high initial antibody response were more likely to detect antibodies in the follow-up test than participants with a low initial antibody response.

The authors state that the findings are important because they show that some previously infected people are more likely to have serum regurgitation and are therefore not considered previously infected.

“Whether the disruption of these antibodies increases the risk of reinfection and the disease remains unresolved,” the authors write. “However, these results may indicate that a single point-in-time serological test may underestimate the number of previously infected SARS-CoV-2 infections, and negative serological test results may be a previous infection. It suggests that we may not definitely exclude. “