Dr. Bob Wachter, University of California, San Francisco’s Grand Rounds moderator and chair of medicine, had two questions he wanted Thursday’s expert speakers to answer: is the Covid-19 delta variant as bad as it gets, and what is the role of rapid testing in determining the future of the pandemic?
“We seem to have turned a corner in our fight against covid, but we’ve turned corners before, only to run into oncoming trains,” Wachter said.
A lesson in evolutionary biology
Dr. Paul Turner, a Yale professor of evolutionary biology, came on first to address the likelihood of any more strains — as in, highly virulent variations.
He pointed to a model by researchers at Emory, who argued SARS-CoV-2 could become a seasonal virus with low population level mortality for a number of reasons, including the relationship between age and severity of disease.
Based on evidence that covid’s mortality rate is strongly dependent on age and that immunity that prevents severe disease is long lasting, the authors argue that covid could become endemic, like the flu.
And, because younger people are less likely to experience severe disease and death, the argument follows that children infected over time are able to build immune responses with lower mortality rates and fewer severe symptoms. When these children are later infected as adults, “the mortality is not going to be seen,” Turner said.
The conclusions of the study, however, don’t seem to be panning out in reality, as the average virulence of covid has actually increased, Turner said.
Asked by Wachter if there is a theoretical limit to how infectious this coronavirus can become, Turner said there are constraints that are being observed across the globe as the viruses converge on similar mutations.
“If you know the boundaries that evolution is likely to travel in its path, then you can more easily head it off at the pass,” he said. Given that the current strain of the virus is “doing very well,” Turner said that delta could be a fitness peak for the virus, but was sure to tack a strong “maybe” onto his statement, much to Wachter’s disappointment.
The future of rapid testing
Dr. Michael Mina, assistant professor of epidemiology at Harvard, then came on to discuss a current hot topic: rapid tests. Yesterday, the White House announced a $1 billion investment for more rapid antigen tests on top of the $2 billion already allotted as part of President Joe Biden’s covid action plan. Mina questioned if this was enough.
Though the goal is to produce 200 million rapid tests per month by December or early 2022, Mina said that, in a nation of 330 million people, this equates to less than five tests per person over the coming year. The plan is not “too little, too late,” he said, but “what we really need to do is unlock high quality rapid tests that are available around the world.”
In the United Kingdom, the government offers free rapid test kits to anyone who wants them, and in Germany, a box of 50 tests costs €37, or less than a U.S. dollar for one test. The United States is a “major outlier” regarding test cost and access. “We have very expensive tests, which aren’t any better than the ones that cost a dollar abroad or are free,” he said. A kit containing two tests costs close to $25 at Walgreens.
While many individuals drive from pharmacy to pharmacy trying to get rapid tests, Abbott Laboratories told employees to destroy millions of tests, “which I would argue is not on Abbott, but is really a reflection of what happens when we place public health fully in the hands of an industry that has a first and foremost responsible to their shareholders,” Mina said.
Tests are not medical devices or prescriptions, Mina argued, but we evaluate and charge for them as though they are. “When the primary beneficiaries of a test are the people around the person who’s using the test then, by definition, it is a public health tool,” he said. Thus, “it needs to be evaluated and treated very, very differently.”
Sensitivity describes a test’s ability to correctly identify individuals who have a disease. Though PCR tests are heralded as the gold standard compared to less sensitive rapid tests, Mina said that rapid tests “have a very unique ability to detect what matters most for public health, which is to answer the question, ‘Am I infectious now?’”
Though an individual will be PCR-positive for 20 to 30 days, they are only transmissible for around five or six. Rapid tests generally pick up infections during this period.
Mina said that tools should be used to identify people before or during that transmissibility period, instead of isolating people who are no longer infectious or quarantining people who were exposed to individuals who weren’t infectious. PCR tests are also slow, difficult to use, and often not easy to access, he said.
Many rapid tests have failed to meet the Food and Drug Administration’s high sensitivity requirements, which may not need to be so high to effectively mitigate the spread of disease.
“Speed and frequency of a test program is absolutely much more crucial in every scenario for public health than the exact sensitivity,” he said.
He advocated for a “test to stay” policy in schools instead, of quarantining kids who are exposed. This would mean if a child is exposed, but tests negative, they could stay in school. Mina also advocated for a “test to treat” approach as covid treatments become more available. If an individual thinks they are sick, with easy access to rapid testing they can quickly find out if they have covid and are infectious, allowing them to start therapeutic treatment early.
Daily rapid tests are generally unnecessary, he said, and instead he suggested schools and workplaces use a dynamic approach to rapid testing and calibrating the frequency to context, such as community rates.
See our previous Grand Rounds coverage here. Grand Rounds will return next week, before going back to its regular once-a-month schedule.