Bryan Anselm/The New York Times

Since antibodies wane post-vaccination, it is likely that booster doses will be needed to curb COVID-19 infection, especially in older individuals.

September 20, 2021

Fighting COVID-19 With Our Immune Systems: The Science of Memory Antibodies

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Although 54.7 percent of the total U.S. population is fully vaccinated for COVID-19 as of Sept. 20, the threat of the highly contagious Delta variant and waning antibodies after vaccination makes vaccine boosters a next step in curbing COVID-19 infections for some. 

According to Prof. Avery August, microbiology and immunology, the purpose of a vaccine is to expose your immune system to what the virus would look like without exposing you to the virus itself, allowing your body to generate infection-fighting antibody proteins. 

During this exposure, B cells — which produce responses from the immune system specific to the new threat — are activated by the presence of the vaccine and then transform into plasma cells, which generate antibodies that recognize the virus.

B cells, which are a type of white blood cell, originate in stem cells in the bone marrow. Some B cells are weeded out in the bone marrow because they are harmful to one’s own cells. The surviving B cells go through a process called hypermutation, in which they undergo changes to select for B cells that can bind foreign antigens the best. 

August explained that B cells can also become memory B cells, which help generate long-lasting antibodies, since they can lie in wait inside the body and quickly respond in the event of subsequent exposure to a specific pathogen. 

According to August, the duration of the body’s antibody response, which can be anywhere from weeks to years, depends on how long the plasma cells survive. 

Prof. Cynthia Leifer, microbiology and immunology, added that the antibody response is also determined by how long a pathogen stays in the body and vaccine potency. COVID-19 recovery can range from a few days to a few weeks. 

Although the original COVID-19 vaccines were highly protective against infection, some are concerned whether this efficacy still holds true against the Delta variant. According to Leifer, it is likely that the antibodies produced from the original vaccine still recognize the Delta variant, though with slightly weaker binding, resulting in slightly lower efficacy. 

However, Leifer emphasized that despite their lower affinity for the Delta variant, antibodies produced from vaccination are still critical for reducing the risk of severe illness from COVID-19.

“The binding is not as strong to the Delta variant, but it’s still significantly strong. So it’s going to really help protect you in the long term,” Leifer said. 

Even though the booster shots will be needed soon, Leifer said that those who have already been vaccinated are still highly protected compared to those who have not been vaccinated. For example, young children are still at risk, as they have not been approved to receive the vaccine yet. 

“The data shows that if you’re fully vaccinated, you’re still very highly protected from serious disease hospitalization and death, which are the most important things to us right now,” Leifer said. 

With booster shot distribution becoming a very likely possibility, medical ethics — determining the order of priority based on risks faced by certain groups — must once more be a consideration for who will be first in line to receive the boosters. According to the Centers for Disease Control and Prevention, if a booster dose is authorized, health care workers, older adults and residents of long-term care facilities will likely be prioritized.

August said that from an immunological standpoint, COVID-19 booster shot distribution should prioritize those who had lower antibody responses in the first two rounds of the vaccine, which can be determined through antibody testing. 

But Leifer said that vaccine availability would not be a hindrance to distribution efforts, due to the excess of vaccines produced from the initial vaccine rollout in the U.S. This will likely result in a smoother distribution of the booster shots. 

“I think right now, we have enough people in the U.S. who are electing not to get the vaccine at all that we have somewhat of an excess. So it’s not as if people getting boosters would take vaccines away from other individuals,” Leifer said. 

While it is unknown how much antibody immunity individuals still have from initial vaccination, immunologists’ main concern is how much additional immunity is necessary for the population to further curb the pandemic. 

“The question is how much antibody immunity we still have, and how much of a reduction have we observed since we’ve been vaccinated that will necessitate significant concern or attempts to generate additional immunity,” August said.