COVID-19: Evaluation of antibody tests welcome but still more info on immunity needed - expert comment19 May 2020
Dr Alexander Edwards, Associate Professor of Biomedical Technology at the University of Reading said:
"There is a lot to celebrate here. Firstly, it’s brilliant to see PHE sharing the main findings of these evaluations of these important products. Secondly, having reliable laboratory antibody tests will help us to build a more detailed picture of viral spread, and be essential to develop the next generation of diagnostic tests.
"What is becoming clear is that these laboratory antibody tests are very specific giving great confidence that they won’t erroneously pick up “false positives”. Neither test is 100% sensitive especially at early times after infection but that’s also not a surprise, and they are both still very useful. Both the Roche and Abbott immunoassay instruments are quite commonly found in UK diagnostic laboratories. Remember these laboratory tests still require a blood sample to be taken- these are not home tests. Whilst so many people who did not get swab tested when they were ill will want to know if they have been infected, it will take significant work to make these tests widely available. They appear to become more accurate at later timepoints after infection, giving best sensitivity >20 days after the start of infection.
"An important point to reinforce however is that antibody tests are not yet going to confirm protective immunity for every individual with a positive result. The way these tests are configured currently is likely to be to detect a wide range of levels of antibody- this can be a very strong antibody response, or a relatively weak one. The reason to detect the weaker responses is to try to detect as many people as possible who have been infected- this is to maximise the “sensitivity”. Antibody tests can try to measure the level of antibody, but we don’t yet have data to know whether the level of antibody is related to protection. Equally importantly, prior science and early studies hint that antibody responses against the “Spike protein” are most important for neutralising virus, which might be important to protect against infection. However, both the Abbott and Roche tests detect antibody against a different protein termed “N”.
"Most people who have recovered would not be expected to become re-infected- but we don’t yet know how strong this protection is or how long it will last. Having this data on test performance is essential so that we can start answering these two critical scientific questions."