Ever since the onset of the coronavirus disease 2019 (COVID-19) pandemic, the causal agent, i.e., severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been mutating leading to different variants. These variants have been classified as variants of interest (VOI) or variants of concern (VOC).
Since the outbreak of the SARS-CoV-2 Omicron (B.1.1.529) variant, in November 2021, it has become the dominant circulating strain worldwide. There is emerging data suggesting that current vaccines are less effective against the Omicron variant and that Omicron is less pathogenic than previous variants.
However, for vulnerable sections of the population, even a less pathogenic variant might have a large impact on morbidity and mortality.
Study: Comparison of vaccine effectiveness against the Omicron (B.1.1.529) variant in patients receiving haemodialysis. Image Credit: mailsonpignata/Shutterstock
A new study has been published on the medRxiv* preprint server, where scientists studied the clinical impact of SARS-CoV-2 Omicron infection, and vaccine effectiveness, in patients undergoing in-center hemodialysis (IC-HD).
Background
The increased transmissibility of the Omicron variant and its ability to evade vaccine and infection-induced protection is a cause of major concern. This has led countries like the UK to bolster the booster vaccination campaigns. Emerging real-world data seem to demonstrate the reduced pathogenicity of the Omicron variant and this mirrors findings in the laboratory, based on animal models. Vaccines have been seen to be less effective against causing the symptomatic infection but more effective against severe infection requiring hospitalization.
It must, however, be noted that for clinically vulnerable individuals, even a less pathogenic variant may have a significant impact on morbidity and mortality. One such vulnerable group comprises individuals suffering from end-stage kidney disease (ESKD) receiving in-center hemodialysis (IC-HD).
Such patients show weak responses to vaccination and some recent studies have shown that even individuals with 3-doses of a heterologous vaccination regimen may have inadequate neutralizing ability against the Omicron variant.
A new study
A total of 1121 IC-HD patients were included in the analysis and all of the patients underwent weekly screening for SARS-CoV-2 infection via RT-PCR testing. Between 1st December 2021 and 16th January 2022, SARS-CoV-2 infection was diagnosed in about 14% of the patients. Almost 93% of those infected were infected by the Omicron variant. Eleven additional cases were attributed to infection by the Delta variant. 6.4% of the patients were unvaccinated, 26.4% were partially vaccinated and 67.3% had received 3-doses of a COVID-19 vaccine.
Key findings
Scientists showed that two doses of the vaccine failed to prevent SARS-CoV-2 infection, against the Omicron variant. The booster vaccine was effective, irrespective of whether the priming was achieved with BNT162b2 or ChAdOx1. Reinfections were found to be common, but the prior infection was observed to be clinically important in reducing the likelihood of infection. This finding was in line with immunogenicity data on immune responses following infection and vaccination. This finding was also in line with the observation that vaccination failed to be effective against hospital admission, but prior infection proved to be more effective.
However, there could be a selection bias in these results in that more co-morbid patients did not survive earlier and more pathogenic variants.
In patients with ESKD, the immunological responses to SARS-CoV-2 vaccines were observed to be weaker and this was true even for the mRNA-based vaccines. A couple of recent in-vitro studies have also shown the necessity of 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 a significant proportion of patients primed with ChAdOx1 had undetectable neutralizing antibodies post the third dose. Researchers of the current study observed no significant difference in clinical outcomes in this primary analysis, but they stated that further monitoring is required.
In comparison to previous waves, the mortality rates in patients with breakthrough infection were much lower. Molnupiravir and Sotrovimab, have both been shown to reduce disease progression in phase 3 clinical trials. However, patients with ESKD were excluded from these trials, which limits the knowledge about the potential safety profile of these medications in hemodialysis patients. Scientists stated that in the current study cohort, no safety concerns were reported, but, limited inference can be made on the use of molnupiravir due to the small sample size.
Concluding remarks
Scientists stated that 3-doses of a SARS-CoV-2 vaccine are required 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 surveillance.
Vaccine regimens and available treatments should be adapted rapidly if the evidence changes.
*Important notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
