There are a lot of articles out there about COVID-19 plasma. Why does it matter to know if you were once infected?

Apart from knowing that you are immune, not at risk, and ok to go to work, immune plasma can potentially be life saving.

We don’t know for sure yet, studies are taking place and it’s not a perfect solution. But here’s how it works.

When you’re infected with a pathogen (virus, bacterium, parasite), your immune system develops antibodies (IgM) to help kill it. But it takes time, and in the meantime you get sick as your immune system tries every tactic to fight the disease. It’s a bit of a race — can the immune system develop antibodies to kill the pathogen before it kills you?

Image for post
Image for post

Eventually, when you recover, your body produces “memory” antibodies (IgG). These IgG antibodies remember that pathogen they saw last time. This is why you usually don’t get infected with the same thing twice.* If the virus enters your body again, the IgG antibodies see it, say “Hey! We’ve seen this before, it’s not good. Let’s get it now.” And they eliminate the pathogen before it has time to replicate and make you sick (and before you can spread it to others).

This is basically the concept of vaccines. A vaccine gives you a fragment of the pathogen, enough to convince your immune system to produce specific antibodies. So when you are infected with the real virus or bacterium, your immune system remembers it and kills it before it hurts you.

The IgG antibodies are specific to that pathogen and only that pathogen. If a different version of the virus appears, they don’t recognize it. This is why you need a new flu vaccine every year. The influenza virus changes often, through mutation or re-assortment. Each year a new version of the flu virus circulates, so we need a new vaccine to target it.

Back to plasma, or “convalescent serum.” Because we don’t have a vaccine for the SARS-CoV-2 virus, we can’t induce antibodies before we are actually infected. When you have COVID-19, your body produces antibodies. Those IgG antibodies hang around and live in your sera. In theory, these antibodies can be taken from a person who has recovered and used to treat someone newly infected. The newly infected person hasn’t had time to develop sufficient antibodies to kill the virus. So instead of waiting for the patient’s immune system to kick in, antibodies from someone else can start attacking the virus, keeping the viral load low until the person’s own immune system mounts a response.

So now it’s important to be able to test people who we think already had the disease to see if they have antibodies that can be used to fight the disease in others.

This isn’t new. We’ve used it to treat Ebola and other diseases. We need to test it first to determine if it works and the best concentrations to be successful. If it does work, it’s not a cure all, but it buys the patient much needed time.

Dr. Rohr-Allegrini is an epidemiologist and tropical disease scientist currently working to prevent diseases through immunizations.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store