What to Know About Antibodies and the COVID Booster Shot

Whether or not we’re going to need a third dose of the vaccine comes down to proteins produced by your white blood cells.

by Erin L. Boyle Health Writer

There’s been a lot of talk about COVID booster shots lately: Will we need one—and when? If you’re like us, you’re probably wondering what the deal is. As it turns out, the deal is hard to get into without getting into another topic first: antibodies.

Antibodies are our main line of defense against viral invaders. Specifically, they’re a protein that our plasma (a type of white blood cell) makes in response to these invaders, also called antigens. In this case, the antigen is the coronavirus. Every antibody binds to one antigen, in its effort to destroy/fight them off. Moreover, a specific type of antibody, known as a neutralizing antibody, has been found to decrease COVID infection in cells.

Neutralizing Antibodies and the COVID-19 Booster Shot

Which leads us to: Pfizer-BioNTech officials recently shared results from their ongoing study looking at a booster shot—a third vaccine dose added to its two-dose regime—saying that this additional dose/booster greatly raised the presence of neutralizing antibodies in the blood, from five to 10 times higher than the two primary doses. Meanwhile, the company has concerns that possible wavering antibody levels in already-vaccinated people might leave them susceptible to the new Delta variant of the virus. Boosting people’s neutralizing antibody levels could help fight off infection, they believe.

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Expert Insight on Neutralizing Antibodies for COVID-19 Prevention

So should we be worried about our antibody counts going down? Are we vulnerable to getting infected again? Who should who most? We talked to Stephen Russell, M.D., Ph.D., CEO and co-founder of Imanis Life Sciences, which makes a test (IMMUNO-COV) to detect COVID-19 neutralizing antibodies, for answers.

HealthCentral: What do our levels of neutralizing antibodies tell us about our protection from COVID-19?

Stephen Russell, M.D., Ph.D.: Neutralizing antibodies are a small but extremely important subset of antibodies we make during a SARS-CoV-2 infection and are the only ones that [appear to] actually block infection. Other antibodies can bind to SARS-CoV-2, but do not inhibit the virus from infecting healthy cells. The decline in neutralizing antibodies after recovery from COVID-19 makes people more susceptible to contracting the virus a second time. Higher levels of neutralizing antibodies have been shown to better protect against new infection.

HC: If the body makes these antibodies in response to COVID, should people who got COVID wait a while before getting the vaccine?

Dr. Russell: There is no compelling reason to wait (unless the vaccine is unavailable). There is currently no evidence to indicate that it will be harmful to receive the vaccine within a short time after recovery from COVID-19. The vaccine will serve to boost the levels of neutralizing antibodies, blocking the ability of the virus to infect healthy cells in the body, hence protecting against reinfection.

While the vaccination is a step in the right direction, we have found that neutralizing antibodies may weaken by 50% by six months. Also, the current notion is that the more severe the case of COVID-19, the more neutralizing antibodies (or immunity to the virus) a person has. While there is a trend, our [data] shows there is in fact no guarantee that severe disease results in higher levels of antibody protection.

HC: How are antibody levels measured?

Dr. Russell: Understanding one’s neutralizing antibody count is one of the most effective ways to stay safe. A quantifiable and scalable neutralizing antibody test like the IMMUNO-COV can monitor antibody levels overtime, so researchers can determine optimal dosing strategies for vaccines, including the administration of vaccine booster doses. In fact, the FDA requires neutralizing antibody quantities be measured in SARS-CoV-2 vaccine trials.

HC: How do antibody counts help determine if we’d need a booster?

Dr. Russell: Neutralizing antibody [levels] are not static over time; they fall quite rapidly in vaccinated subjects, as much as five- to 10-fold over a six-month period. Taking into account the fact that peak antibody [levels] are highly variable between vaccinated individuals and that they fall at a variable rate, it is quite possible that a fully protected vaccine recipient could remain protected for over a year, or they could lose their protection in three months. The appropriate timing of booster shots is therefore very difficult to determine without specific information about the peak neutralizing antibody titer and its rate of fall in a given individual.

HC: Is there a specific level of neutralizing antibodies that ensures safety from the virus?

Dr. Russell: In a nutshell, low levels of antibody titers are less protective than high levels. In a study recently published in Nature Medicine, the paper’s authors compared the neutralizing antibody titers in subjects convalescing from COVID-19 with those from people who had been vaccinated. Within each of these populations, there was a wide spread of neutralizing antibody levels, indicating that some vaccine recipients and some convalescent individuals are much better protected than others.

HC: Could people who are immunocompromised or over 65 have lower levels of neutralizing antibodies with our current COVID vaccine regimes?

Dr. Russell: Yes, it is possible for immunocompromised people and those over age 65 to have less neutralizing antibody titers, as level of immunity varies from person-to-person. There is emerging data surrounding the efficacy of the COVID-19 vaccine among immunocompromised people; generally, elderly and immunocompromised patient populations are more prone to infection and are thus considered more vulnerable to COVID-19. Those with weakened immune systems should abide by CDC guidance for unvaccinated people by practicing social distancing, wearing a mask and limiting unnecessary travel.

HC: Which COVID-19 vaccines appear to be creating the strongest antibody counts?

Dr. Russell: The Pfizer and Moderna vaccines appear to generate the highest neutralizing antibody titers, followed by the AstraZeneca and Johnson & Johnson vaccines, and then the SinoVac vaccine, which produces the lowest titers.

HC: How does the rate of decline in the COVID vaccine effectiveness compare to the flu or other vaccines?

Dr. Russell: Different vaccines work differently. It remains a possibility that a vaccine might be developed for COVID-19 that gives lasting immunity. Common childhood vaccines such as measles, mumps, and rubella typically result in lifelong immunity, but they use live replicating viruses which may persist much longer than mRNA vaccines and are therefore able to drive a more lasting immune response.

Erin L. Boyle
Meet Our Writer
Erin L. Boyle

Erin L. Boyle, the senior editor at HealthCentral from 2016-2018, is an award-winning freelance medical writer and editor with more than 15 years’ experience. She’s traveled the world for a decade to bring the latest in medical research to doctors. Health writing is also personal for her: she has several autoimmune diseases and migraines with aura, which she writes about for HealthCentral. Learn more about her at erinlynnboyle.com. Follow her on Twitter @ErinLBoyle.