Is vaccine status associated with the severity of Omicron SARS-CoV-2 infection in hospitalized patients?

In a recent study posted to the medRxiv* preprint server, researchers assessed the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on the occurrence and severity of symptoms in SARS-CoV-2 Omicron-infected hospitalized patients.

Background

Compared to the SARS-CoV-2 Delta variant of concern (VOC), the enormous number of coronavirus disease 2019 (COVID-19) infections reported during the Omicron surge were accompanied by a lower case-fatality rate. This novel VOC fueled curiosity about the effects of vaccination on both an individual and a community level about whether COVID-19 vaccines intrinsically decreased the risk of severe infection. Research so far has given only a partial picture of the scenario since a majority of mild cases are not hospitalized or not even diagnosed.

About the study

In the present study, researchers determined whether vaccination status was related to the severity of SARS-CoV-2 Omicron infection in hospitalized patients.

A retrospective, multicenter investigation was conducted across 14 hospital centers in Bulgaria, Croatia, France, and Turkey. Notwithstanding the reason for hospitalization, hospitalized patients having a polymerase chain reaction (PCR)-confirmed SARS-CoV-2 diagnosis between 1 December 2021 and 3 March 2022, were included in the study. A patient was deemed fully vaccinated if that were immunized with a minimum of one Ad26.CoV2-S injection, two ChAdOx1-S, and/or messenger ribonucleic acid (mRNA) vaccines such as tozinameran and elasomeran, with the last dose administered at least 14 days prior to the PCR diagnosis. 

Results

The study cohort included 1215 hospitalized patients, 746 of whom had received all vaccine doses, whereas 469 had received none. Most vaccinated patients who had complete records of their vaccinations had either received solely tozinameran or a combination of the two mRNA vaccines. More than two dosages were administered to 395 patients. Although no significant variance was noted between vaccinated and unvaccinated patients with respect to the number of comorbidities, vaccinated patients were more likely to be slightly older, be men, and have specific comorbidities.

Unvaccinated patients displayed more severe COVID-19 infections and were more likely to be hospitalized due to COVID-19 than any other reason that was incident with diagnosis of an asymptomatic COVID-19. Furthermore, their lung involvement was comparatively extensive on computed tomography (CT) scan. Unvaccinated patients also needed oxygen supplementation more often, for longer periods at a higher flow. They were also more likely to require immunomodulatory therapy, including steroidal anti-inflammatory drugs. Notably, the vaccine's protective impact was more prominent at an older age.

The primary outcomes considered included oxygen supplementation, the requirement for intensive care unit (ICU) admission, and 28-day mortality. In bivariate analysis, patients who were older, were male, and had comorbidities were significantly linked to one or more negative outcomes. Multivariate analysis showed that the protective effect of immunization was maintained with respect to oxygen requirement, ICU admission, and the risk of death. Vaccination also mitigated and essentially eliminated the detrimental effects of several comorbidities. Kidney failure, solid or hematological cancer, and older age were independent risk factors that could lead to more severe outcomes, including death. Only the need for oxygen was significantly impacted by pulmonary illnesses, which tended to have a negative effect on the result.

Compared to Delta-infected patients, Omicron-infected patients showed less severe infection, irrespective of their vaccination status. Regardless of vaccination status, Omicron-infected patients had significantly lower median C-reactive protein (CRP) and extended lung lesions on CT scan, were less likely to need oxygen supplementation, steroid therapy, high-flow oxygen therapy, ICU admission, and had lower 28-day mortality rates.

In multivariate analysis, infection with the Omicron VOC was linked to fewer deaths, lesser need for oxygen therapy, and fewer ICU admissions. Immunization against SARS-CoV-2 and prior SARS-CoV-2 infection also protected disease severity. The interactions observed between vaccination and immunosuppression showed that protection elicited after vaccination against the need for ICU admission was reduced among immunosuppressed patients. On the other hand, the interaction noted between vaccination and a history of SARS-CoV-2 infection showed that patients with prior SARS-CoV-2 infections may benefit less from immunization.

Conclusion

Overall, the study findings showed that vaccination with adenovirus-based and mRNA-based vaccines were significantly effective against the severity of SARS-CoV-2 Omicron infection.

*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.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.