Study finds COVID-19 infection followed by vaccination produces higher antibody levels

POLITICS

Those who survived COVID-19 and then got vaccinated have more durable antibodies, study finds

Published Monday, November 1, 2021 5:11PM EDT

In this file photo, a researcher tests possible COVID-19 antibodies in an Eli Lilly laboratory in Indianapolis, in May 2020. (David Morrison / Eli Lilly via AP)

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TORONTO -- A study of nearly 2,000 vaccinated health-care workers, some of whom had contracted COVID-19, has found that those who survived the virus and then received an mRNA vaccine have a higher number of long-lasting antibodies.

The results of the study were described in a research letter

“This finding adds to our understanding of how immunity against SARS-CoV-2 works, and builds upon an earlier study by our team that showed the mRNA vaccines yielded a robust antibody response, even if a person did not develop significant symptoms following vaccination or did not have a prior SARS-CoV-2 infection,” Aaron Milstone, professor of pediatrics at the Johns Hopkins University School of Medicine and senior author of the study,

In order to study the antibodies, researchers followed 1,960 health-care workers from Johns Hopkins Medicine in Maryland who had received both doses of either the Pfizer-BioNTech COVID-19 vaccine or the Moderna jab.

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Of those 1,960 workers, 73 had previously tested positive for COVID-19 prior to being vaccinated.

Researchers split the 73 workers into two further groups to test whether the time between recovering from the infection and getting vaccinated made a difference, dividing them into those who had COVID-19 within 90 days of their first shot, and those who were exposed more than 90 days before their first shot.

All 1,960 participants gave a serum sample at least 14 days after receiving their second shot, and the samples were tested for antibody levels at one month, three months, four-and-a-half months and six months after receiving the second shot.

Those who had a prior infection before getting vaccinated had higher levels of antibodies than those who only were vaccinated, and their antibody levels remained more durable over time.

“We found that health-care workers with prior SARS-CoV-2 infection followed by two doses of mRNA vaccine — therefore, three independent exposures to the S1 spike protein — developed higher antibody levels than those with vaccination alone,” Diana Zhong, M.D., an infectious diseases fellow at the Johns Hopkins University School of Medicine and lead author of the study, said in the release. “The relative differences were 14 per cent higher at one month following the second vaccine dose, 19 per cent at three months and 56 per cent at six months.”

In addition, those who contracted COVID-19 more than 90 days before their first shot had higher antibody levels post-vaccination than those who contracted COVID-19 within 90 days of the first dose.

“This suggests that a longer interval between infection and first vaccine dose may enhance the antibody response,” Milstone said.

Researchers acknowledged that the study had limits, such as the smaller proportion of participants who had COVID-19 in the past, and the fact that they only measured antibody production levels, and not neutralization titers in the blood.

It's important to note that the findings don’t suggest contracting COVID-19 before getting vaccinated. Other research has shown that the virus can cause severe infection and even death in people of any age or health level, and doctors still don’t fully understand the long-lasting effects of the virus on the human body. But the new study does reinforce that those who were infected with COVID-19 previously would benefit from receiving a vaccine.

Researchers stated in the release that further research is needed to understand “the interplay between natural or vaccine derived immunity.”