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Frequent administration of rapid-turnaround tests could substantially reduce COVID-19 infectiousness and curb the virus’s spread, researchers at Harvard School of Public Health and the University of Colorado at Boulder found in a new study.
While the gold-standard tests, which detect the virus using polymerase chain reaction, accurately identify infected patients, they are not highly effective for population-wide testing due to lengthy return times, according to James A. Hay, a postdoctoral researcher at the School of Public Health and one of the study's authors.
“One of the problems with testing has been that we've been kind of restricting ourselves to these very sensitive PCR tests that are really not designed for mass deployment,” Hay said.
Those administering the tests should prioritize accessibility, frequency, and turnaround time over “test sensitivity” — meaning the proportion of infected individuals who test positive — according to the study, which was published November 20 in the peer-reviewed journal Science Advances.
Though the rapid COVID-19 tests have less sensitivity than the gold-standard PCR tests, they bring other benefits: Some return results in 15 minutes, while PCR tests can take several days.
“That loss of sensitivity is offset by the fact that they're very cheap to produce, they're very easy to use, and they're the sort of thing you can give to people to use in their homes,” Hay said.
“The key is that by testing people very frequently, you're much more likely to catch people when they're infectious,” Hay added.
The lower sensitivity of the rapid, at-home tests compared to standard PCR tests means patients must have higher viral loads for the test to detect the virus. But in most cases, patients do not become contagious until after the brief early period of infection, when people tend to have lower viral loads that are undetectable by the at-home tests, according to Hay.
Hay said the tests should be viewed as a transmission-limiting tool aiding public health response, rather than purely as a medical diagnostic like the standard PCR tests. In a School of Public Health press release, epidemiology professor Michael J. Mina, a senior co-author and Hay’s postdoctoral advisor, called the tests “contagiousness tests.”
“These rapid tests are contagiousness tests,” Mina said in the release. “They are extremely effective in detecting COVID-19 when people are contagious.”
Even with frequent testing via rapid COVID-19 tests, social distancing measures will remain critical, Hay said.
“Rapid testing is more a way to say, well, we can detect more positive people and earlier in their infection, and it's for those people who test positive that they must take extra precautions to not infect other people,” Hay said. “Those are the people that we would encourage to self isolate, but it doesn't mean that if you get a negative result that's a free passport to do whatever you want.”
“At the population level, if we are targeting who has to self isolate much more intelligently, then we don't need to resort to the kind of population-wide lockdowns, because we know that the people that are self isolating are those that are positive,” he added.
He also said successful execution of a rapid testing plan still requires investment and action from the government at a federal or state level.
“This sort of analysis should be very good motivation to go up to the federal level or state level and start thinking, well, we need to start producing these tests on mass, so this will be effective if we deployed this sort of strategy at a high frequency,” Hay said. “It's not something that will just instantly change the situation.”
“We need investment in infrastructure, we need investment in messaging, we need investment in encouraging people to follow this sort of advice,” he added.
—Staff writer Virginia L. Ma can be reached at email@example.com.
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