There is a new antibody test that will change the landscape of Covid-19 testing as we know it.
There are now two ways to test for Covid-19: one that measures the actual virus, and one that measures the body’s reaction to the virus.
The first is a genome test that detects the presence of viral genes in the body using a swabbed sample, usually taken from the nose and throat. The sample must then be sent to a lab where it can be replicated and analyzed in a PCR machine. Results could take anywhere from one day to a week and a half to deliver. Point-of-care genome tests have also been developed that can potentially shorten this waiting period to mere minutes.
The second, which only recently has received FDA approval in the United States, is an antibody test, or serology test, that detects the presence of SARS-CoV-2 specific antibodies in the blood. Instead of a nasopharyngeal swab, results are obtained using a finger prick blood test. Like the point of care genome tests, antibody tests are a rapid diagnostic that will give users a verdict within minutes.
One potential use of antibody tests is to measure the extent of the pandemic at the population level. Our understanding of the disease and its projected impact in the United States is weakened by our inability to monitor its spread amongst people with either mild symptoms or none at all.
Another use is to measure the progress of individual infection. Antibody tests quantify the number of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in the blood. The presence of more IgM antibodies, which are the first to appear and mobilize against an invading organism, indicates more recent exposure to the virus. It is through this result that an asymptomatic carrier of the virus could be identified—a feature of no small importance, since “silent carriers” have played a major role in transmission.
More IgG antibodies, which are virus specific and produced in later stages of infection, would lead a person to test positive for immunity, implying recovery. This unfortunately doesn’t guarantee full protection. The test won’t reveal how neutralizing, or how potent, these IgG antibodies are; nor can it determine how long they will last. With certain families of coronaviruses, including the beta coronavirus family that includes SARS-CoV-2, reinfection has been found to occur, and for now it remains a possibility.
Even with this taken into account, the advantages of antibody tests as a tool against infectious disease are still numerous—their low cost not least among them. Antibody tests can be administered for less than $10 each in the United States, and even less in other countries. The price is but a fraction of the PCR tests, which hover around $50 for Medicare patients. No special assembly or training is required; tests could be given in clinics and pharmacies, or at schools and popup stations.
Successful deployment of antibody tests, as The Economist so succinctly put it, will depend on their “sensitivity and specificity.” Sensitivity prevents false negatives, since a more sensitive test is more likely to actually detect it. Specificity, on the other hand, prevents false positives, since a less specific test may pick up on antibodies against a virus other than SARs-CoV-2. Either way, once an antibody test proves to be as sensitive and specific as constraints will allow, it must be distributed nationwide for maximum effect.
If it is still difficult to imagine how one rapid diagnostic test could reach the majority of American citizens, consider the example of a country that has done it before: Egypt. Since October 2018, the Ministry of Health’s 100 Million Healthy Lives program has used serology tests to screen more than 60 million Egyptians 12 years of age or older for hepatitis C, diabetes, hypertension, and obesity. The tests cost about 50 cents per person and come back in as little as five minutes. Results are logged and correlated with factors like age, sex, weight, blood pressure, and so on.
It would take a concerted effort, but in the United States we have the infrastructure and manpower it takes to conduct rapid antibody tests quickly, cheaply, and at a massive scale. The small European country of Andorra has plans to give antibody tests to its entire population. Compared to other resource rich nations, we’ve failed to answer the WHO director general’s call to “test, test, test.” That can change—but only if we act now, and act fast.