How to do smarter coronavirus testing
With testing once again a huge vulnerability to America’s coronavirus response, public health officials are calling for a revamped strategy that features the use of more tests, even if they're imperfect.
Why it matters: The system is overwhelmed by the demand for tests, and yet prolific testing is key to identifying asymptomatic or pre-symptomatic coronavirus cases. Experts say the solution is smarter testing — which doesn't require perfect accuracy.
The big picture: Most coronavirus diagnostic tests right now are PCR tests, which are highly accurate, but relatively slow and expensive. But other kinds of tests exist; they just carry the risk of more false negatives.
- Some experts argue that, when doing mass testing, the tests don’t need to be 100% accurate. Catching, for example, even 50% of unidentified cases is better than the much-lower percentage that we’re catching today.
- “By putting a premium on the accuracy of tests, we fail to test a majority of people with COVID-19 and these built in delays actually undermine our ability to timely identify cases which is the key purpose for widespread testing,” Harvard’s Ashish Jha recently wrote in a TIME op-ed.
Between the lines: Strategy is key, and who gets which test matters.
- In a white paper calling for a national testing strategy, former FDA Commissioner Mark McClellan, Johns Hopkins’ Caitlin Rivers and Duke’s Christina Silcox last week wrote that symptomatic patients and people who are close contacts of known cases should still receive PCR or other highly-accurate diagnostic tests.
- But “for people without symptoms, we also need broad availability of more rapid but sometimes less accurate screening tests...to detect outbreaks sooner and give people more confidence in their workplaces and schools,” they write.
- “This is particularly important for high-risk populations such as nursing homes, essential workplaces, and hard-hit communities that currently have limited resources for testing.”
Details: There are several alternative testing options. Antigen tests are faster and cheaper than PCR tests, but less accurate. The FDA has already authorized two companies to sell antigen tests, per Science, and others are in the pipeline.
- Pool testing is another way to stretch limited resources. This is where multiple samples are tested together, and each individual sample is only tested on its own if the pooled sample comes back positive. But this is only effective in populations with low caseloads; otherwise, too many pooled samples come back positive.
Yes, but: Many insurers don’t pay for tests that aren’t “medically necessary,” which generally includes screening or surveillance testing.
- The absence of a guaranteed demand could be depressing the creation and mass production of these alternative tests.
- “Without clear funding or screening protocols, test manufacturers are not getting a clear signal for investing in much larger testing capacity for the months ahead,” McClellan, Rivers and Silcox write.
What we’re watching: Six states announced last week that, in the absence of a national testing strategy, they’re banding together in partnership with the Rockefeller Foundation to buy 3 million rapid point-of-care antigen tests.
- If this goes well, it could provide a model for how states — or even the federal government — can evolve their testing strategies.