This post was updated on 4/27/20 to reflect new information.
According to an interview given in early April, by Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, the federal government was thinking about using “immunity certificates” to help open up parts of the U.S. economy over the course of the next few months.
The hope is that widespread testing for antibodies in the blood of people throughout the U.S. will help us understand how many people have already been infected, and therefore, are potentially immune to the new coronavirus. This may allow some of us to slowly resume routine activities.
This concept has already been put into practice by researchers in Germany, and other European countries are looking into issuing some sort of “immunity passport.” Cities in China are also using this concept to label citizens so that severe lockdowns can be eased.
But, the key word here is potentially. Dr. Fauci points out that some countries have started to try this and “have gotten burned.”
Now the WHO is warning against the use of immunity “passports” because they may provide people with a false sense of security.
There are many other things we need to know before we can use antibody tests to help us emerge from strict physical distancing:
- Does having antibodies in your blood mean that you are immune? This is a very complicated question. Studies show that it takes about 1- 2 weeks after infection for antibodies to show up in the blood. Depending on the infection, antibodies can stay in the blood and provide immunity for months, years, and sometimes our whole lives. Right now, we are assuming that the presence of antibodies means that we have some level of immunity for a period of time – but we really don’t know. We still need to figure out if these antibodies are neutralizing antibodies (meaning that not only are they present, but that they are able to kill the infection so we don’t get sick again). As the WHO points out, as of today, no study in humans has shown that antibodies to the new coronavirus actually leads to future immunity.
- Does having these antibodies mean you aren’t contagious anymore? Another question that we don’t have a definite answer to yet. Studies are showing that some people carry the virus around for much longer than we thought, even after their symptoms are gone. So we’ll need more time to figure out if and how long people are contagious after they have recovered. Most experts think that people are most contagious at the beginning of the infection.
- How long will immunity last? Data from SARS and MERS (2 other deadly coronaviruses), showed that antibodies were present up to 2-3 years in the case of SARS and about 1 year in the case of MERS. We still don’t know how long antibodies can protect us from COVID-19 reinfection. This information would affect how often people would need to be rechecked for immunity.
- How accurate are the antibody tests? Like all tests, the new antibody tests will need to be validated to make sure that the results they provide are consistent and accurate. Even in tests that are highly sensitive and specific, when you test large numbers of people you are going to get some fraction of false positives and false negatives (meaning people that are immune but are found to be NOT immune—and even more concerning, people that are not immune but are found to be immune). It’s not clear if some tests cross-react with antibodies from other types of coronavirus infections. This is critical to make sure that the tests are only finding antibodies for the new coronavirus, and not previous infections from viruses that cause the common cold.
There are also many practical and ethical questions about issuing certificates, like – How would we guard against fraudulent certificates? Could certificates be used to discriminate against the non-immune?
With so many factors playing a role in immunity testing, it’s very important to take a cautious approach. As countries start relaxing lockdowns, regardless of their antibody status, people will still need to be mindful of physical distancing, wearing masks, washing hands, and limiting time in places with many people until an effective vaccine and treatments are accessible.
You can follow Dr. Neha Pathak on Twitter @NehaPathakMD for regular updates about Covid-19 and information about other public health emergencies.