A nationwide data analysis confirms that SARS-CoV-2 antibody responses to vaccination decrease rapidly in dialysis patients, leaving them at risk of breakthrough infection, reports Annals of Internal Medicine.
The researchers analyzed real-world data on 4791 patients receiving care in a large US network of dialysis facilities. Residual plasma from routine monthly tests performed at a central laboratory was used to measure qualitative and quantitative antibodies to the SARS-CoV-2 receptor-binding domain (RBD). The analysis began in January 2021, before COVID-19 vaccines were widely available. By mid-September 2021, 2563 patients were fully vaccinated.
Trends in antibody levels were assessed, including the possible association between antibody titers and the risk of breakthrough COVID-19 infection. Among vaccinated patients, the estimated rate of undetectable RBD responses increased from 6.6% at 14 to 30 days after vaccination to 20.2% at 5 to 6 months. Median index values decreased from 91.9 to 8.4, respectively.
During follow-up, clinically documented COVID-19 occurred in 2% of fully vaccinated dialysis patients, compared with 3% of partially vaccinated (one dose) and 11% of unvaccinated patients. In a nested case-control analysis, each breakthrough case was matched to five controls for age, sex, and vaccination month, with adjustment for diabetes status and region.
The analysis included 56 patients with breakthrough infections, with samples collected a median of 21 days before diagnosis. Waning of the antibody response was significantly associated with the risk of breakthrough infection. Compared with an index RBD range of 23 or higher (reflecting an antibody level of 506 binding antibody units per milliliter), rate ratios for breakthrough infection were 11.6 at pre-breakthrough RBD values of less than 10 and 6.0 at values between 10 and 23. Peak antibody responses were higher for patients with evidence of previous SARS-CoV-2 infection, although this difference lessened during follow-up.
SARS-CoV-2 antibody levels after vaccination are “strongly associated” with the risk of breakthrough COVID-19 infection in dialysis patients, the study concludes. The findings have implications for efforts to define a “persisting antibody” threshold for protection against COVID-19, which may be especially important for high-risk or immunocompromised patients. The researchers note that 40% of dialysis patients with breakthrough infections were hospitalized [Anand S, et al. SARS-CoV-2 vaccine antibody response and breakthrough infection in patients receiving dialysis. Ann Intern Med, published online ahead of print December 14, 2021. doi: 10.7326/M21-4176; https://www.acpjournals.org/doi/10.7326/M21-4176].