COVID SCIENCE-Antibody test reliability faulted; new predictor of COVID-19 severity

July 30 (Reuters) - The following is a roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for COVID-19.

Antibody tests can miss previous COVID-19 infection

Antibody tests do not reliably confirm that someone has had COVID-19, which means global estimates of infection rates are likely inaccurate, according to researchers. "We studied the blood of over 120 people with confirmed COVID-19 and measured levels of antibodies ... using 14 different tests" up to three months after diagnosis, said Michael Peluso of the University of California, San Francisco. "All of these people definitely had COVID-19, but not all of them had positive COVID-19 blood tests." The accuracy of the tests at confirming prior COVID-19 varied by how sick the person had been, how much time had passed since the illness and which test had been used. "People who were less sick and in whom more time had passed were less likely to test positive using certain tests," Peluso said. "Since most people have mild (or even asymptomatic) infection with SARS-CoV-2, this study has important implications for our interpretation of several of the large studies that have been done ... to try to estimate the number of people who have had COVID-19." In a report published on Friday in the journal Science Advances, his team advises, "Individual patients or providers using these assays to assess the presence or absence of prior infection and/or immune status should take these considerations into account, given the poor negative predictive value of some tests."

Early response in nose may predict severe COVID-19

How cells in the nose respond to the coronavirus might someday be used to predict how sick a person will become with COVID-19, according to a new study. Researchers analyzed immune activity in cells taken from patients' nasal swabs at the time of COVID-19 diagnosis, comparing those who became only mildly ill to those who eventually required mechanical support with breathing. "When our cells in the nose meet a virus like SARS-CoV-2 ... the ways that they sound the alarm to generate a rapid antiviral response vary greatly across people," said Jose Ordovas-Montanes of Harvard University. "Individuals who went on to develop severe COVID-19 had a significantly muted alarm system," regardless of how much virus was present, Ordovas-Montanes said. Lack of a strong initial antiviral response might allow the virus to spread more rapidly, increasing the chances that it can move from the upper to lower airways, Ordovas-Montanes and colleagues suggest in a report published in the journal Cell "If further studies support our findings, we could use the same nasal swabs we use to diagnose COVID-19 to identity potentially severe cases before severe disease develops, creating an opportunity for effective early intervention," study co-author Carly Ziegler, a graduate student at Harvard and the Massachusetts Institute of Technology, said in a press statement.

“Killer T cells” provide early defense after mRNA vaccine

The moderate drop in COVID-19 risk seen after just one shot of a two-dose mRNA vaccine is not due to vaccine-induced antibodies but to immune cells called killer T cells, a new study showed. At that point, the antibodies are still barely detectable, German researchers reported on Wednesday in the journal Nature They studied 32 volunteers who received the Pfizer/BioNTech vaccine, collecting blood samples before the first dose and every few days afterward for up to four months after the second dose. "Seven to 10 days after the first dose ... killer T cells are already detectable in the blood," said study co-author Christoph Neumann-Haefelin of the University of Freiburg. "These killer T cells are able to contain a SARS-CoV-2 infection by killing infected cells, and also by production of antiviral substances that suppress viral spread." Neutralizing antibodies, which are likely the main players in preventing infection because they block the virus from invading cells, are produced in substantial amounts only after the second vaccine dose, Neumann-Haefelin said. "Our results underscore the importance of complete vaccination with two doses of the mRNA vaccine for adequate protection against infection," Neumann-Haefelin added.

High “breakthrough” infection rate in Massachusetts county

A study by the U.S. Centers for Disease Control and Prevention and Massachusetts researchers showed that three-quarters of people who became infected with COVID-19 at public events in a Massachusetts town had been fully vaccinated. The study, published in the CDC's Morbidity and Mortality Weekly Report on Friday, identified 469 people with COVID-19, of whom 74% were fully vaccinated, following large public events in Provincetown, on Cape Cod. Testing identified the Delta variant in 90% of virus specimens from 133 people. A separate CDC internal document, first reported by the Washington Post on Friday, described the Delta variant as being as transmissible as chickenpox and cautioned that it could cause severe disease. On Tuesday, the CDC reversed course on guidance for wearing masks, calling for their use in areas where cases are surging as a precaution against the possible transmission of the virus by fully vaccinated people. The new study's authors recommended that local health authorities consider requiring masks in indoor public settings regardless of vaccination status or the number of coronavirus cases in the community.

Click for a Reuters graphic on vaccines in development.

Reporting by Nancy Lapid and Manas Mishra; Editing by Will Dunham