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COVID-19 testing for first responders: Understanding antibody tests and immunity

Not all COVID-19 antibody tests are created equal – an important point to consider when determining who is best serving on the front lines


As the national conversation turns to re-opening, testing and data-based decisions are taking center stage as the key to understanding the pandemic – and who is safe to return to work.

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First responders are used to being “essential” and on the front lines of any disaster – natural or manmade. The current pandemic is no exception and has required organizations to pivot their policies, practices and response in an unprecedented manner.

While the rest of the nation has been ordered to stay at home or shelter in place, first responders have been told not only to keep working, but also to show up to all the homes and establishments at the highest risk.

As the national conversation turns to re-opening, testing and data-based decisions are taking center stage as the key to understanding the pandemic – and who is safe to return to work.

For first responders, the conversation and testing decisions are even more pertinent, as many have been consistently exposed and are at high risk of both suffering from and carrying the virus.

Unfortunately, much remains unknown about what testing should look like, how reliable it is, who should get it, and when.

Two types of tests

There are two categories of COVID-19 tests: polymerase chain reaction (PCR) tests and antibody tests.

The PCR tests determine if someone has the infection. Clearly, if a first responder tests positive for the infection, they should follow the standard recommendations of quarantine to avoid spreading the virus to coworkers and the public.

Antibody tests do not test if someone currently has the virus, but rather for antibodies after the fact. Antibodies are typically present in the blood anywhere from a few days to a couple weeks after the body has been infected. One downside of antibody tests is that, if you test too soon after infection, there are higher rates of false negatives where the test says you do not have antibodies when, in fact, you do.

Within antibody tests, there are different types as well. Enzyme-linked immunosorbent assays (ELISA) tests detect and measure the level of antibodies in the blood. These require a blood draw and a lab for testing. Point-of-care tests, or lateral flow tests, require only a finger stick but do not test the amount of antibody present, just whether they are present, and can produce a positive, negative or borderline result, which indicates the infection was likely recent.

Not all COVID-19 antibody tests are created equal, though.

Antibody tests: Sensitivity and specificity

The key to understanding the effectiveness of a test is looking at sensitivity and specificity. Sensitivity is the number of true positives from a test while specificity is a true negative of a test. Ideally, you would want every test to find all the true positives and all the true negatives, but that rarely happens. While most companies marketing tests have reported good sensitivity and specificity in their pre-market testing, there is evidence that – once they took their products to market and started using them on a large scale – the accuracy of the tests were much lower than initially believed.

Currently, only one antibody test has been approved by the FDA. As of April 7, 2020, the FDA has been notified by more than 70 companies that they have blood tests available for use. The FDA has allowed companies to market tests even without approval as emergency use with the caveat that companies have to continue testing and submit their findings to the FDA. Several market their products as FDA-approved, but – to date – only four have such approval.

The availability and accuracy of testing is rapidly evolving, and a good deal remains unknown – a fact that should be considered when making decisions about first responders and testing.

It’s important to note that antibody tests are more likely to report false negatives early on and don’t detect active cases of COVID-19. Particularly for a first responder who has just been infected, the infection could be missed.

Early data suggests that some tests, in practice, have poor sensitivity and specificity, which means it could give people a false sense of security.

Questions of immunity

While it is assumed that people who have had the infection develop immunity based on how other viruses have behaved, enough time has not elapsed to know if this is true for the current virus, how much antibody you have to have to develop immunity, or how long the immunity lasts.

There are instances of people who have been known to have the virus, recovered, but do not test positive for antibodies. This could be a fault of the test or it is possible that not everyone produces antibodies. Antibody testing may also miss people who are immunocompromised.

While tracking of the genome of the virus suggests its evolution is slow and the eight known strains appear to act similarly, it is changing as it evolves. It is possible that not all tests can detect all strains.

Even given the unknowns, it does not mean there is not a role for antibody testing with first responders. Rather, it suggests that testing alone should not be considered the answer. People who test positive for the antibodies – if it is a true positive – may have immunity and be better suited to serve on the front lines. However, no one should become complacent and assume a positive test means they are definitely immune.

How to proceed

The answer – as always – is to continue best practices of PPE use and cleaning. First responders have to act as though they and everyone they come in contact with has the virus, regardless of testing.

In the interim, it is important for first responders in particular to be engaged with tracking and testing as it evolves and as opportunities present themselves. And it is more important than ever for first responders to be engaged in research.

Several tracking programs are being developed at the local, regional and national levels. As an example, more than 2 million people have already signed up to report their daily symptoms through the COVID-19 Symptom Tracker.

Now is the time to focus on symptoms, track your health and connect with department leadership about making smart staffing decisions.

Sara Jahnke, PhD, is the director and a senior scientist with the Center for Fire, Rescue & EMS Health Research at the National Development & Research Institutes - USA. With over a decade of research experience on firefighter health, Dr. Jahnke has been the principal investigator on 10 national studies as well as dozens of studies as a co-investigator. Her work has focused on a range of health concerns, including the health of female firefighters, behavioral health, risk of injury, cancer, cardiovascular risk factors, and substance use, with funding from the Assistance to Firefighters Grant R&D Program, the National Institutes of Health and other foundations. Jahnke has more than 100 publications in the peer-reviewed medical literature. Awards include the 2019 Endowed Lecture at the annual conference of the American College of Epidemiology; the 2018 President’s Award for Excellence in Fire Service Research as well as the Excellence in Research, Safety, Health & Survival Award, both from the International Association of Fire Chiefs (IAFC); and the 2016 John Granito Award for Excellence in Firefighter Research from the International Journal of Fire Service Leadership and Management. Connect with Jahnke on LinkedIn, Twitter or via email.