(p. A5) “Retrospective studies are great and they provide some hints, but there are caveats,” said Dr. Shyam Kottilil, a professor of medicine with the Institute of Human Virology at the University of Maryland School of Medicine. “It’s very difficult to establish causality.”
Interest in the cross-protective effects of vaccines has led to efforts to repurpose old vaccines that may have potential to provide at least transient protection against the coronavirus until a specific vaccine against SARS-CoV-2 is developed and proven safe and effective, he said.
“But nobody knows whether this approach will work unless we test them,” Dr. Kottilil said. “To endorse this, you need to do really good randomized clinical trials.” There is little incentive for private companies to invest in expensive trials because the old vaccines are cheap and off-patent, he added.
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(Note: the online version of the story has the date July 29, 2020, and has the title “Old Vaccines May Stop the Coronavirus, Study Hints. Scientists Are Skeptical.”)