Understanding the presence of adaptive immune responses that are associated with protection against disease (potential protective immunity) caused by SARS-CoV-2 at the population level is critical for public policy. Potential protective immunity can be acquired through vaccination or previous infection.
We used vaccination history or the presence of antibodies specific for the receptor binding domain (RBD antibodies) of the spike protein of the SARS-CoV-2 virus as potential markers of potential protective immunity, as both are strongly associated with the presence of neutralizing antibodies. Antibodies.
We conducted surveys and serological testing in a representative community sample to estimate the fraction of the Los Angeles County (LAC) adult population that had potential protective immunity in April 2021. We tested for differences in potential protective immunity by demographics and whether the presence of RBD antibodies decreased with time since infection.
Discussion
This study found that in April 2021, approximately 72% of adults in LAC had potential protective immunity against SARS-CoV-2. Despite this high level of population immunity and continued vaccination efforts, Los Angeles County experienced an increase in COVID-19 cases in July 2021, suggesting that achieving herd immunity could be more difficult. than expected.
Rates of potential protective immunity were much lower for Black people and those from low-income households, justifying increased vaccination efforts for these communities. The findings also suggest a much higher cumulative incidence of infection in high-poverty areas, which likely contributed to the stark socioeconomic disparities in COVID-19 mortality rates observed.
Almost all unvaccinated people with prior infection had RBD antibodies, although many participants had infections several months before antibody testing. This suggests that RBD antibodies were not decreasing.
The study has limitations. We use self-reported vaccination and antibody presence as a marker of immunity rather than, for example, measuring cell-mediated immunity. Although we weight our estimates to match the percentage of confirmed cases and the percentage vaccinated, the 2 most important factors associated with protective immunity, we cannot rule out selection bias.
Comments
Herd immunity against COVID-19 is unlikely, and addressing the disease will likely depend on vaccination, treatment and ensuring adequate hospital capacity, says a new study conducted in Los Angeles County.
With herd immunity, most people have antibodies from vaccination or a previous infection, so a virus has fewer people to infect and stops spreading.
At the beginning of the pandemic, there were hopes that herd immunity would end it, but this new study suggests that is unlikely.
"As new variants continue to result in significant increases, even in a place like Los Angeles County, which had some of the strictest mask mandates and most extensive testing capacity in the country, we must shift our pandemic response from minimizing infections to minimizing the harm of infections," said Neeraj Sood, director of the COVID Initiative at the Schaeffer Center for Health Policy and Economics at the University of Southern California.
Researchers estimated that as of April 2021, about 72% of adults in Los Angeles County had COVID-19 antibodies through vaccination or prior infection.
Despite that high rate of people with antibodies, COVID cases in the county have nearly doubled since last April, according to findings published in the journal JAMA Network Open .
Black adults and those from lower-income households had much lower rates of protective immunity overall, despite having higher rates of antibodies from past infections, the study found.
"These communities were hit on both sides: They generally had lower vaccination rates, especially in the first few months that vaccines were available, and they were also hit harder by previous waves of COVID," Sood said.
The pandemic has exposed serious health disparities in Los Angeles, said Howard Hu, chair of the Department of Population and Public Health Sciences at the Keck School of Medicine of USC. "Going forward, we must redouble our efforts to reduce these disparities."
The results suggest that policymakers and public health officials should reconsider the long-term goals for addressing COVID-19 and how to make the best use of resources.
"Testing the symptomatic, ensuring access to new treatments and encouraging vaccinations for high-risk populations should be pillars of our pandemic response going forward," Sood said.
"These findings indicate that preventing COVID surges may be increasingly unrealistic , but we can ensure that our health care system and hospitals have the capacity they need and that patients have the care they need," he added.
