Recovering From COVID-19 Doesn’t Guarantee Antibodies or Confer Immunity to Re-Infection

Thomas McDade in his lab at Northwestern University tests for antibodies to SARS-CoV-2 (the virus that causes COVID-19). Credit: Northwestern University

COVID-19 Antibody Study Shows Downside to Not Receiving Second Injection

A new study shows that two months after the second Pfizer/Moderna vaccination, the antibody response decreases by 20% in adults with previous cases of COVID-19. The study also tests how well current vaccines resist emerging variants.

The Northwestern University study underscores the importance of receiving a second dose of vaccine, not only because it is well known that vaccine immunity wanes over time, but also because of the risk of emerging variants, including the highly contagious delta-type variant.

The study also showed that previous exposure to SARS-CoV-2 does not guarantee a high level of antibodies or a robust antibody response to the first vaccine dose. This directly contradicts the assumption that contracting COVID makes one naturally immune to reinfection. The findings support vaccination (and two doses) even for people who have contracted the virus before.

A team of scientists, including biological anthropologist Thomas McDade and pharmacologist Alexis Demonbreun, tested blood samples from adults who tested positive for SARS-CoV-2 to measure how long the immunity benefits of Pfizer and Moderna vaccines last and how well they protect against newer variants.

The study participants were selected from a racially and ethnically diverse sample of adults from the Chicago area who had been recruited at the start of the pandemic. Using lab-developed antibody test kits, participants submitted blood samples two to three weeks after their first and second vaccination doses and two months after the second dose.

Antibody response after second shot

In the lab, the researchers tested for neutralizing antibodies by measuring whether the blood sample could inhibit the interaction between the virus’s spike protein and the ACE2 receptor — this interaction is how the virus causes infection once it enters the body.

“When we tested blood samples from participants collected about three weeks after their second vaccine dose, the mean inhibition level was 98%, indicating a very high level of neutralizing antibodies,” said McDade, a professor of anthropology at the Weinberg College of Arts and Sciences. and a fellow faculty member at the university’s Institute for Policy Research.

The scientists tested emerging variants B.1.1351 (South Africa), B.1.1.7 (UK) and P.1 (Brazil) and found that the rate of inhibition of viral variants was significantly lower, ranging from 67% to 92% .

Antibody response decreased after two months

In test samples collected two months after the second dose, they found an approximately 20% decrease in antibody response.

The researchers found that the antibody response to vaccination varied based on a history of previous infection.

Individuals with clinically confirmed cases of COVID-19 and multiple symptoms had a higher response rate than those who tested positive but had mild symptoms or were asymptomatic.

“Many people and many doctors assume that any previous exposure to SARS-CoV-2 will confer immunity to reinfection. Based on this logic, some people with previous exposure think they should not get vaccinated. Or if they do get vaccinated, they think they only need the first dose of the two doses of Pfizer/Moderna vaccines,” McDade said.

“Our study demonstrates that prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor a robust antibody response to the first vaccine dose. For people who had mild or asymptomatic infections, their antibody response to vaccination is essentially the same as in people who have not been exposed before.”

McDade adds that although the research was conducted before the emergence of the delta virus, the conclusions are similar.

“In terms of protection after vaccination, the story is the same for all variants, including delta – the vaccine offers good protection, but not as good protection as the original version of the virus the vaccine was designed for. Combine that with the fact that the immunity wanes over time, you get an increased vulnerability to breakthrough infections.

“So, it’s two strikes now — delta plus waning immunity in the first wave of vaccinees,” McDade said.

Reference: “Durability of Antibody Response to Vaccination and Surrogate Neutralization of Emerging Variants Based on SARS-CoV-2 Exposure History” Aug 30, 2021, Scientific Reports.
DOI: 10.1038/s41598-021-96879-3