I usually disagree with MikeyH because he is often very negative, however today he does raise some interesting questions in respect to the apparent inconsistencies reported by Saudi Vac today between the Sensitivities of the Symptomatic and the Asymptomatic Covid positive patients. His argument would be: why does the Sona test pick up 100% of the Asymptomatic patients but only 83.3% of the Symptomatic ? (still within FDA guidelines by the way) and the suggestion would be that the Sona test is not reliable enough. A reasonable conclusion at face value.
It is, however not quite as simple as that, and the clue may be revealed in that the Symptomatic patients were all hospitalised.
There was a very interesting article published in the NY Times on Aug 29th which referenced DR Michael Mina, expert Harvard Epidemiologist , among others and you should read the whole article if you are interested enough, as it addresses this very theme, but I have included a few quotes below:
"Some of the nation’s leading public health experts are raising a new concern in the endless debate over coronavirus testing in the United States: The standard tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus."
"Most of these people are not likely to be contagious, and identifying them may contribute to bottlenecks that prevent those who are contagious from being found in time. But researchers say the solution is not to test less, or to skip testing people without symptoms, as recently suggested by the Centers for Disease Control and Prevention."
"Tests with thresholds so high may detect not just live virus but also genetic fragments, leftovers from infection that pose no particular risk — akin to finding a hair in a room long after a person has left, Dr. Mina said."
"In Massachusetts, from 85 to 90 percent of people who tested positive in July with a cycle threshold of 40 would have been deemed negative if the threshold were 30 cycles, Dr. Mina said. “I would say that none of those people should be contact-traced, not one,” he said."
The suggestion is that patients who have had Covid for prolonged time ( eg. those hospitalised as in the Sona trial) may not still have active infection but have genetic RNA fragments hanging around which are detected by the very accurate PCR machines but have no clinical relevance and that these patients are no longer infectious and cannot pass on the virus. This argument, which has been made before and is gathering force, would adequately and exactly explain why Sona picked up 100% of the Asymptomatics but not some of the possibly long-term hospitalised. This, if confirmed, would be FANTASTIC NEWS for Sona and we should expect to hear more as it would mean that Sona´s test picks up exactly those infected who are responsible for the majority of the virus spread and doesn´t waste time on the no-longer infectious.
The sample size is acceptable for FDA purposes as they ask for 30 positives and 30 negatives in the total Test Population not in each group. If you were to look for 30 Asymptomatic patients you would probably have to recruit around 500 patients or more and no-one is being asked to do that.
The results reported by Saudi Vac suggest that the Sona test, using the GNRs to increase detection and provide exceptional Sensitivity in Low Viral Loads ie. Asymptomatic patients is exactly what the world needs.
Saudi Vac themselves say that the test is ideal as a Screening Tool for the Saudi Ministry of Health and others are bound to follow. It is the only test, so far, that can claim this and even if the FDA drags its´ heels there will be plenty of demand elsewhere.
In Massachusetts, from 85 to 90 percent of people who tested positive in July with a cycle threshold of 40 would have been deemed negative if the threshold were 30 cycles, Dr. Mina said. “I would say that none of those people should be contact-traced, not one,” he said.