Coronavirus infections may be more common, study finds


In the weeks following the epidemic of coronavirus that has shattered everyday life in America, researchers have struggled to assess the true spread of the virus. But initial results from a study in Northern California on anti-coronavirus antibodies suggest it has circulated much more widely than previously thought, according to a report released Friday.

The preliminary study, conducted by researchers at Stanford University, estimates that between 2.5% and 4.2% of Santa Clara County residents had antibodies to the new coronavirus in their blood in early April. Antibodies indicate that a person’s immune system has responded to a past infection.

Although the county reported around 1,000 cases in early April, Stanford researchers estimate that the actual number is between 48,000 and 81,000.

Santa Clara County was one of the first epicenters of the COVID-19 pandemic in California. By sampling the blood of 3,300 county residents and testing it for anti-coronavirus antibodies, the researchers hoped to estimate the prevalence of the virus in the population.

Antibody blood tests, also known as serological tests, are separate from diagnostic tests used to confirm an active infection.

Investigators from the Los Angeles County Public Health Department and the USC launched a similar study a week after Santa Clara began its efforts. Officials say they will release their initial results on Monday.

Barbara Ferrer, the county’s highest public health official, said that although the Los Angeles study will have somewhat different figures, “They will tell a similar story. And I think the story is … many more people have been infected with COVID-19 than those captured by our tests. “

The discrepancy, Ferrer explained, is due to the slow start of diagnostic tests for coronaviruses and the fact that many people with little or no symptoms have not been tested.

There are important caveats to Santa Clara’s conclusions. Unlike Los Angeles County, where researchers recruited a random sample of participants to reflect the composition of the county, the Northern California study recruited social media participants.

As a result, white women aged 19 to 64 were over-represented in the pool of participants, while Latinos and Asian Americans were under-represented relative to their share of the county’s population. The researchers tried to correct this imbalance in their analysis.

In addition, the Stanford report has been posted on a website to share the first results of medical research and has not yet been reviewed through the typical peer review process.

Neeraj Sood, a professor at the USC Price School of Public Policy, author of the Stanford report, said he was not surprised by the results.

“I didn’t know how big it would be, but we certainly expected there to be more cases than what was confirmed, just because of the scarcity of testing,” said Sood, who is also the principal investigator of the Los Angeles County study. .

One of the main findings of the Santa Clara County study is that a large number of people infected with the coronavirus have no symptoms, said Karin Michels, chair of the epidemiology department of the Fielding School of Public Health at l ‘UCLA.

The fact that these people can be contagious without knowing it means that a certain level of physical distance must remain in place to protect the elderly and those suffering from underlying diseases who are much more at risk of the disease.

“How do we protect vulnerable people, while leaving others who may be immune because they have been infected and have antibodies return to work?” How do you sort that? Said Michels.

Antibody detection can help provide a response, she said, but only if a large part of the population is able to get tested.

Studies suggest that perhaps 30% to 50% of people who get the new coronavirus have no symptoms, said Dr. Bob Wachter, chair of the Department of Medicine at UC San Francisco. At some point, he said, there will have to be strategic tests on asymptomatic people.

Officials and researchers are increasingly pointing out that antibody testing is essential in determining when and how to loosen the movement and trade restrictions that have resulted in an unprecedented economic closure.

Knowing the true extent of the virus’s reach can shed light on how close people are to collective immunity, in which enough people have a certain degree of immunity to the virus which makes it difficult to spread infections.

These tests can also provide a more accurate picture of virus mortality. Currently, the death rate is based on the number of confirmed infections, but the higher the number of infections, the lower the death rate.

Based on their results, the Stanford researchers estimated the death rate in Santa Clara County between 0.12% and 0.2%. In comparison, the average death rate from seasonal flu is 0.1%.

Sood said it was too early to offer policy prescriptions based on the initial findings, noting that further study would provide more information on the death rate and the rate of spread of the disease.

Its goal in Los Angeles County is to repeat the study every two to three weeks over the course of several months, in the hopes of generating more data to inform the models that officials use to plan their response to the coronavirus.

“We need to integrate this data into these models, then determine what the conclusion is,” he said.

Experts from the World Health Organization warned on Friday that it is too early to assess the extent to which antibody tests indicate immunity.

Maria Van Kerkhove, Acting Head of Emerging Diseases at WHO, said there is no evidence yet that rapid serological tests can reveal immunity to the coronavirus.

“At the moment, we have no evidence that the use of a serological test can show that an individual is immune or protected against reinfection,” she said.

Serological tests measure the level of antibodies to the virus the body creates a week or two after infection, she said.

But scientists don’t yet know if people who have antibodies to the virus are immune.

“We will be issuing guidelines on this over the weekend as it is a confusing area,” said Van Kerkhove.

Dr. Michael Ryan, executive director of the WHO Health Emergency Management Program, echoed his concern.

“People have to look in detail at the protection that antibodies could give,” he said. “No one is sure that someone with antibodies is completely protected against the exposure and recurrence of the disease. “

Times writer Maura Dolan in San Francisco contributed to the report.


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