Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, the causative agent, i.e. severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has mutated, resulting in different variants. These variants were classified as variants of interest (VOI) or variants of concern (VOC).
Since the outbreak of the SARS-CoV-2 Omicron variant (B.1.1.529), in November 2021, it has become the dominant strain circulating in the world. New data suggest that current vaccines are less effective against the Omicron variant and that Omicron is less pathogenic than previous variants.
However, for vulnerable segments of the population, even a less pathogenic variant could have a large impact on morbidity and mortality.
A new study has just been published on medRxiv* preprint server, where scientists studied the clinical impact of SARS-CoV-2 Omicron infection and vaccine efficacy in patients undergoing in-center hemodialysis (IC-HD).
The increased transmissibility of the Omicron variant and its ability to evade protection induced by vaccines and infections is a major cause for concern. This has led countries like the UK to step up booster vaccination campaigns. Emerging real-world data appear to demonstrate reduced pathogenicity of the Omicron variant and this mirrors findings in the laboratory, based on animal models. Vaccines have been shown to be less effective against symptomatic infection, but more effective against serious infections requiring hospitalization.
It should be noted, however, that for clinically vulnerable individuals, even a less pathogenic variant can have a significant impact on morbidity and mortality. One such vulnerable group includes people with end-stage renal disease (ESKD) receiving in-centre hemodialysis (IC-HD).
These patients show weak responses to vaccination and some recent studies have shown that even individuals receiving 3 doses of a heterologous vaccination schedule may have inadequate neutralizing capacity against the Omicron variant.
A new study
A total of 1121 IC-HD patients were included in the analysis and all patients were screened weekly for SARS-CoV-2 infection via RT-PCR test. Between December 1, 2021 and January 16, 2022, SARS-CoV-2 infection was diagnosed in approximately 14% of patients. Nearly 93% of those infected were infected with the Omicron variant. Eleven additional cases were attributed to Delta variant infection. 6.4% of patients were unvaccinated, 26.4% were partially vaccinated, and 67.3% had received 3 doses of a COVID-19 vaccine.
Scientists showed that two doses of the vaccine failed to prevent infection with SARS-CoV-2, against the Omicron variant. The booster vaccine was effective whether the primary vaccination was performed with BNT162b2 or ChAdOx1. Reinfections were found to be common, but prior infection was found to be clinically important in reducing the likelihood of infection. This finding was consistent with immunogenicity data on immune responses after infection and vaccination. This finding was also consistent with the observation that vaccination was not effective against hospitalization, but prior infection was found to be more effective.
However, there could be selection bias in these results as more comorbid patients did not survive earlier and more pathogenic variants.
In patients with ESKD, immunological responses to SARS-CoV-2 vaccines were found to be weaker and this was true even for mRNA-based vaccines. Some recent in vitro studies have also shown the need for a booster dose in dialysis patients. The first study reported no difference between patients primed with ChAdOx1 and an mRNA vaccine. The second study showed that a significant proportion of patients sensitized with ChAdOx1 had undetectable neutralizing antibodies after the third dose. The current study researchers found no significant difference in clinical outcomes in this primary analysis, but said further monitoring was needed.
Compared to previous waves, death rates in patients with breakthrough infections were much lower. Molnupiravir and sotrovimab have been shown to reduce disease progression in phase 3 clinical trials. However, patients with ESKD were excluded from these trials, limiting knowledge of the safety profile potential of these drugs in hemodialysis patients. The scientists said that in the current study cohort, no safety issues have been reported, but limited inference can be made about the use of molnupiravir due to the small sample size.
The scientists said 3 doses of a SARS-CoV-2 vaccine are needed for clinical protection against the Omicron variant, for hemodialysis patients. Although this variant appears to result in less severe clinical outcomes, this high-risk population requires close monitoring.
Vaccine schedules and available treatments need to be adapted quickly if the evidence changes.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.