I’m Covid Antibody Negative Despite Being Fully Vaccinated; Is That a Problem?
A physician looks at how our immune systems respond to the Covid vaccine
I received my second dose of the Pfizer-BioNTech Covid-19 vaccine on January 4th of this year. I donated blood on March 19th. The donation center routinely checks for antibodies to Covid-19 in their donors. To my surprise, I was antibody negative. Does that mean my vaccine didn’t work?
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The short answer is, “no.” Here are two reasons why I’m not concerned, and if you find yourself in a similar situation, you need not worry either.
1) Antibody tests aren’t perfect
Not all antibody tests are the same. There are a number of different classes of antibodies or immunoglobulins (Ig). For instance, IgM is made by the body early in the course of an illness, but levels of IgM decline sharply within days to weeks. On the other hand, IgG antibodies aren’t produced until later in the course of an illness but tend to last for months, or even years, after an infection has resolved.
Furthermore, the body manufactures antibodies to many different viral proteins, also called antigens. An individual who was previously infected with the novel coronavirus, SARS-CoV-2, may possess antibodies, for example, to the nucleocapsid antigen but perhaps not to the envelope antigen. So, if a test is performed that only measures antibodies to the envelope antigen, then the result in this example would be a false negative.
The Covid vaccine stimulates the body to produce antibodies only to the spike protein and not to other parts of SARS-CoV-2. That means for a vaccinated patient who never had a natural infection, testing for antibodies to proteins other than the spike would produce a negative result.
Writing this article prompted me to look further into the test performed at the time of my blood donation. It was actually a series of two tests. The first portion tested for antibodies that can occur after either natural infection or vaccination. This actually turned out positive in my case. The second portion tested for the non-spike antibodies seen only with natural infection, which led to the negative result I was so surprised to see on my patient file. Overall, these two tests imply that I indeed carry antibodies to Covid-19 as a result of the vaccine but none from natural infection. This makes sense because, as far as I know, I was never infected with Covid-19.
2) Antibodies aren’t the only way to fight infection
Even if I had no detectable antibodies to Covid-19, though, it wouldn’t necessarily mean the vaccine didn’t work. Antibodies are just one way the immune system can fight infection. Another method is called cellular immunity and involves specific immune cells called T-cells that, by way of a vaccine or natural infection, can learn to recognize viral proteins and destroy a would-be pathogen before it has a chance to harm its host.
In addition to promoting antibody production, the Covid vaccine also generates cellular immunity. Like antibodies, cellular immunity tends to wane over time but typically outlasts the life of antibodies in the blood.
Thankfully, all three Covid vaccines approved in the United States have exceeded expectations and are upwards of 72% effective at preventing symptomatic infection and more than 86% effective at preventing severe disease. This high degree of effectiveness is independent of whether or not an individual has measurable antibodies. Time will tell if and when booster doses of the Covid vaccine will be indicated, but for now, it is my hope that more and more people will take advantage of the life-saving protection these vaccines afford.