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The work, conducted in Gallatin County over a year, sought to assess how long antibodies could last after COVID-19 and compare that to the protection provided by COVID-19 vaccines.

A team of scientists from Montana State University's Department of Microbiology and Cell Biology published research earlier this month evaluating the effectiveness of COVID-19 vaccines and seeking to learn more about how long the resulting antibody protection may last.

The study, "Titers, Prevalence and Duration of SARS-CoV-2 Antibodies in a Local COVID-19 Outbreak and Following Vaccination" published in the journal Vaccines, was conducted using volunteer subjects and data collected in Gallatin County beginning in March 2020, shortly after the first COVID-19 cases were reported in Montana. Around 170 volunteers had their blood drawn — many on a monthly basis — to assess whether there were antibodies present and, if so, how the titer, or concentration of antibodies in the blood, changed over time.

For associate research professor Jodi Hedges, the study provided an opportunity to conduct real-time research on a public health issue in her community. As more Montanans and Americans receive vaccines, she said the study was a way to engage the public in critical science.

"I loved the fact that the volunteers were up for coming back to give samples every month for a year," she said. "The enthusiasm for the project and encouragement of the participants was great. It was fun to be able to tell them their antibody status in a time of such uncertainty. This whole project was really gratifying."

The research team also included Deann Snyder, instructional lab manager for the Department of Microbiology and Cell Biology, research associate Amanda Robison, associate professor Matt Taylor and Regents professor Mark Jutila.

Antibodies are an immune response triggered by exposure to something foreign, like a virus, said Hedges, who led the study. Humans produce antibodies both in response to natural infection and after vaccination. The higher the concentration of antibodies, the more an individual is protected from future infection. But a major question was whether a symptom-less case of COVID-19 triggered a measurable antibody response.

"We wanted to measure the extent of asymptomatic infection by measuring antibodies in people," Hedges said. "What if a bunch of us already had antibodies?"

As it turned out, asymptomatic infection in the community was less prevalent than initially thought, especially when a person hadn't been in close contact with someone diagnosed with COVID-19. But Hedges and her team found that asymptomatic infection still led to an antibody response, so they sought to learn more about those antibodies.

"We were interested from a diagnostic standpoint, to see how long after infection we could see if someone had had it, as well as to see how long that protection lasted," said Hedges.

For most study participants, antibody levels began to wane after five or six months, the team found. For those with the highest starting levels of antibodies, the time before antibody levels dropped could be as long as a year.

Hedges noted that the human antibody response triggered by a vaccine is much stronger. For maximum protection, she said, even those who have already had and recovered from the virus should be vaccinated.

"It's an important takeaway from this that there's a lot of variability. Just because you had it, it doesn't mean you have a strong antibody response," she said.

Part of the reason that immunity lasts longer after vaccination is because of memory B cells, said Hedges. A type of blood cell, memory B cells retain a genetic blueprint for the antibodies they create, meaning they can continue to create those same antibodies in the future. Memory B cells can be maintained in the body for decades, well after antibody levels have waned.

Hedges explained that these cells are why many modern vaccines administered to young children can provide protection for their entire lifetime. Memory B cells are created after natural infection, but in a lower concentration than is triggered by a vaccine, meaning the immune response is stronger after vaccination.

"Groups have measured memory B cells in people in their 90s and 100s who have memory B cells from the 1918 flu pandemic," she said. "If you made antibodies once, you have the memory B cells to make them again.