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 Are you Immune?
Don Mosier, MD, PhD | Rimini Road

The resumption of normal activities as the COVID-19 epidemic begins to wane will depend upon either effective immunity to the coronavirus or a potent antiviral drug. Immunity could result from the majority of the population having recovered from the virus (called “herd immunity”). The most recent results from tests for COVID-19 antibody suggest that infection rates are in the 1-2% range in California, far below the 60% needed for herd immunity. These results are preliminary because the antibody tests used have not been validated, the results have not been peer reviewed, and they have not been replicated by additional studies. More on this issue later.

Effective immunity could also be elicited by a coronavirus vaccine. Although there is an international effort to generate and test candidate vaccines, the most optimistic prediction is that it will take 1-2 years to have a vaccine for general use. Given the problems producing enough reagents for virus testing, it is likely that scaling up production of a vaccine needed by most of the world population will take considerable time.

At this time there are over 120 potential antiviral compounds in various stages of testing. Some are repurposed drugs that have already been approved by the Federal Drug Administration (FDA) for other diseases, and these can undergo large-scale efficacy trials (called phase 3 studies) in the immediate future. If some of these are effective against the coronavirus, we could have treatment options as soon as 6 months from now.

There currently is an urgent need to test for antibodies against the virus. The FDA has allowed test kits to be marketed without its approval, a decision prompted by its slowness to approve virus test kits. The result is over 90 different antibody tests of widely varying quality. Some tests have poor sensitivity so they miss people who have been infected. Others have poor specificity so they generate false positive results if you have been infected with other viruses such as the common cold. If the false positive rate is 5% (as documented in some of these tests) but the incidence of real infection is 1-2%, then many people tested with these assays will assume they are immune to the virus when they are not. They then might relax protective measures and become new targets for COVID-19 spread.

Four FDA-approved antibody tests are currently available for use in certified clinical testing laboratories, and results from these tests are reported to the San Diego County Health Department. Office or drive-thru tests are not reported to the health department, so they do not add to the number of infected individuals reported daily. UC San Diego is offering validated antibody screening for individuals who think that they might have been exposed to the virus, although initial efforts were focused on healthcare workers. The testing center is at the Center for Advanced Laboratory Medicine at UC San Diego.



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