As the 2019 coronavirus disease (COVID-19) pandemic, caused by the novel cornonavirus SARS-CoV-2, continues to spread across the globe, the need for more testing has become painfully apparent. Current tests rely on a method called quantitative polymerase chain reaction (qPCR), which can detect the presence of viral genetic sequences. Besides limited availability of the test, qPCR has other drawbacks. It can only detect active infections of the virus and cannot determine who has already had it and recovered. Additionally, the test appears to have a high false negative rate, which may explain why some patients are considered recovered only to test positive again. In contrast, a serological test can detect whether someone has antibodies against the virus, which persist after recovering from the disease.
A recent report from Florian Krammer’s lab at Mount Sinai details a new serological test that could scale to test large numbers of people. The work is a preprint, meaning it has not been peer-reviewed and officially published. The test looks for the presence of antibodies that target the spike protein of SARS-CoV-2. The spike is a protein that sticks out of the fatty surface of the virus, so it is a prime target for antibodies. This test uses purified spike protein that was made in the lab, so it does not involve the use of any live virus. The first step is to stick spike protein to the bottom of small plastic dishes. Then, different concentrations of patient serum are placed in the dish so that if any antibodies are present, they will stick to the spike on the bottom. Finally, a machine detects the presence of patient antibodies quantitatively. Importantly, the test does not give false positive results for patients who were exposed to a different coronavirus.
Serological tests are an important complement to the current testing standards. They will help estimate how many people were infected with the virus but never showed symptoms. This has important implications for modeling the spread of the virus and informing containment strategies. Although it hasn’t been demonstrated directly, it is likely that anti-spike antibodies from recovered patients could be effective in preventing or treating COVID-19 since they might block the virus’s normal interaction and signal the immune system. Overall, these tests can be used to identify potential serum donors and to find health-care workers with higher levels of immunity to perform the tasks with higher exposure risks.
Managing correspondent: Julian Segert
Original article: A serological assay to detect SARS-CoV-2 seroconversion in humans MedRxiv
Image credit: Wikimedia Commons