Delta and Omicron Variants Partially Evaded COVID-19 Vaccines, Study Indicates
Summary
- Dr. Alberto Caban-Martinez contributed to a study that showed vaccinated people’s immune responses to newly emerged versions of the SARS-CoV-2 virus showed less specificity to these variants.
- Vaccinated participants had higher overall levels of antibodies for both Delta and Omicron infections than their unvaccinated counterparts. However, after Delta infections, vaccinated participants had only about half as many Delta-specific antibody-producing cells.
- The findings shed light on how vaccination affects the immune system’s response to evolving viral threats.
The original COVID-19 vaccines protected against disease and saved lives. However, a new study published in Nature Immunology, and co-authored by researchers with the University of Miami Miller School of Medicine, uncovers a caveat. Vaccinated people’s immune responses to newly emerged versions of the virus showed less specificity to these variants.
Essential workers and others who contracted the Delta or Omicron variants after being vaccinated produced stronger responses with higher levels of antibodies overall than their unvaccinated counterparts. However, the team’s analysis uncovered deficits in their ability to target the mutated parts of the variant specifically.
“While COVID-19 vaccination is effective, its ability to prime the immune system to mount the most targeted response really depends on the type of variant that’s in circulation at the time,” said study co-author Alberto Caban-Martinez, D.O., Ph.D., M.P.H., a professor and vice chair for research in the Department of Public Health Sciences and associate vice provost for research integrity, regulatory affairs and assessment at the Miller School.
The findings shed light on how vaccination affects the immune system’s response to ever-evolving viral threats, according to senior author Deepta Bhattacharya, Ph.D., a professor of immunology at the University of Arizona College of Medicine – Tucson.
“What we really wanted to address is this fundamental question of how the immune system adapts when you’re exposed to a virus and then the virus changes. Are you able to generate new responses against those new mutations?” Dr. Bhattacharya said.
The Threat of Evolving Viruses
After the initial strain of SARS-CoV-2, the COVID-causing virus, swept the planet in early 2020, the pathogen evolved, leading to successive waves of infection. Later that year, the more infectious Delta variant emerged. Omicron, which was still more contagious yet caused less severe disease, showed up in late 2021. The new study draws on data by the RECOVER study, which ran until 2023 and was funded by the U.S. Centers for Disease Control (CDC).
Researchers at six RECOVER sites, including the University of Miami site led by Dr. Caban-Martinez, who is deputy director of the Sylvester Firefighter Cancer Initiative, regularly gathered nasal swabs and blood draws from those at highest risk of contracting COVID-19: health care personnel, first responders, including firefighters, and other essential workers. The new study relied on CDC-funded project data collected in part at the University of Arizona, from the HEROES-RECOVER cohorts, and included participants who were not essential workers.
Dr. Bhattacharya’s team used this data to investigate a phenomenon known as antigenic imprinting. It occurs when exposure to or vaccination against one strain of a virus appears to “lock in” the immune system, making it less able to adapt to new variants, according to Dr. Caban-Martinez. (The COVID vaccinations they studied were based on the original SARS-CoV-2 strain.)
Toward Better Boosters
Vaccinated participants had higher overall levels of antibodies for both Delta and Omicron infections than their unvaccinated counterparts. However, after Delta infections, vaccinated participants had only about half as many Delta-specific antibody-producing cells, called memory B cells, that persist in the body long after an infection clears. This result suggests vaccination suppressed this form of long-term immunity to Delta, according to Dr. Caban-Martinez.
While the responses to Delta showed signs of antigenic imprinting, the same was not true of Omicron. In these infections, vaccinated and unvaccinated alike showed weak responses, with few Omicron-specific antibodies or memory B cells.
The antigenic imprinting effect the study uncovered for Delta is likely too minor to interfere significantly with immunity. The lack of a targeted response to Omicron represents a more significant challenge. To make booster shots for COVID-19 and perhaps other viruses more effective, vaccine makers need to employ strategies that overcome this evasiveness and produce variant-specific responses, according to the researchers.
This study and others drawing on RECOVER data have given Dr. Caban-Martinez and his colleagues a chance to reflect on what they saw during the pandemic, including differences in the protection that vaccination appeared to confer against the original virus and its variants.
“The immune system’s ability to produce new, variant-specific responses isn’t just blocked by vaccine history,” Dr. Caban-Martinez said. “It also depends on the variant itself is. Some variants like Delta can still trigger decent new responses. Others, like Omicron BA.1, don’t, even without prior vaccine bias.”
Tags: coronavirus, COVID-19, COVID-19 vaccine, Dr. Alberto Caban-Martinez, SARS-CoV-2