Scientists have developed several vaccines to stop infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of the continuing coronavirus disease 2019 (COVID-19) pandemic. Previous studies have shown that although vaccine-induced immunity declines over time, vaccine effectiveness (VE) against severe COVID-19 persists for prolonged periods. 

Study: Protection of Two and Three mRNA Vaccine Doses Against Severe Outcomes Amongst Adults Hospitalized With COVID-19—VISION Network, August 2021 to March 2022. Image Credit: Prostock-studio / Shutterstock.com

Background

Several studies have indicated that COVID-19 vaccines were less effective in stopping severe illness in older adults and otherwise immunocompromised patients. Nevertheless, COVID-19 vaccination has reduced disease severity amongst patients hospitalized attributable to SARS-CoV-2 infection. 

Fully vaccinated individuals who were hospitalized attributable to symptomatic COVID-19 were less more likely to require mechanical ventilation, intensive care unit (ICU) admission, or die as in comparison with unvaccinated individuals. Nevertheless, there stays a scarcity of studies which have evaluated the connection between COVID-19 booster vaccination and disease severity using large samples infected with different SARS-CoV-2 variants. 

Concerning the study

A recent Journal of Infectious Diseases study investigates the effect of COVID-19 vaccination on severe infections that required hospitalization. The researchers also explored residual confounding aspects using COVID-19-negative controls and a difference-in-differences method.

The VISION Network is a collaboration of United States healthcare systems and research centers that gives vaccination, in addition to medical and laboratory records. Patients who were above 18 years of old without immunocompromising conditions and were hospitalized for over 24 hours attributable to COVID-19-like illness (CLI) between August 19, 2021, and March 28, 2022, were included within the study cohort. All relevant information on these patients was available at VISION Network sites.

A test-negative control cohort comprised patients with negative molecular assay results for COVID-19 inside 14 days before and 72 hours after hospital admission. This study included fully vaccinated individuals with two doses of a messenger ribonucleic acid (mRNA) COVID-19 vaccine and those that received the booster or third dose. Unvaccinated individuals were also included for comparative evaluation.

All eligible participants who were fully vaccinated with two COVID-19 mRNA vaccines were further divided into two groups. These groups included a ‘two-dose recent’ group, which included individuals who received their second vaccine dose lower than 150 days prior to the index date, and a ‘two-dose distant’ group comprising individuals who received their second vaccine dose 150 days or more prior to the index date.

To research disease severity attributable to COVID-19, ICU admission, in-hospital death, and length of hospitalization were considered.

Study findings

A complete of 27,149 individuals were hospitalized attributable to COVID-19, 59.2% and 40.8% of whom were hospitalized throughout the SARS-CoV-2 Delta and Omicron dominant periods, respectively. These participants were included within the test-positive cohort. It was observed that 75% of the hospitalized individuals were unvaccinated. 

As in comparison with the vaccinated group, unvaccinated individuals were much younger. Typically, the younger age group is less more likely to have underlying comorbidities, similar to diabetes and cardiovascular conditions. 

The next attenuation in disease severity prevailed amongst those that received the booster vaccine than those that accomplished the two-dose vaccine regime. This might be attributable to the waning of vaccine-induced immunity, which was re-instated after the booster dose.

Consistent with previous studies, the COVID-19 mRNA vaccine exhibited decreased effectiveness against severe infection attributable to the Omicron variant as in comparison with the Delta variant.

Typically, less protection against severe illness was observed in two-dose recent vaccinees as in comparison with two-dose distant or three-dose booster vaccinated patients. This might be attributable to the presence of an unknown factor not considered throughout the evaluation.

The negative control group helped discover potential residual confounding aspects after controlling for medical comorbidities and demographic aspects, similar to sex, race, urbanicity, and age. Finally, a difference-in-differences approach was applied to regulate for unmeasured aspects, with all findings indicating that vaccination lowered disease severity. 

Limitations

The present study has several limitations, including the consideration of COVID-19 tests that were conducted in medical settings and those who performed at home or in public health sectors were ignored. Subsequently, a lot of COVID-19 patients weren’t included on this study.

As well as, information regarding COVID-19 prevention and coverings, similar to antiviral medications and monoclonal antibodies, weren’t considered. Notably, these interventions would influence a person’s disease trajectory. 

The difference-in-difference approach didn’t consider the explanations for hospitalization amongst vaccinated and unvaccinated patients. The complete spectrum of clinical symptoms amongst vaccinated and unvaccinated groups was not investigated; due to this fact, the role of vaccines in reducing meaningful outcomes couldn’t be determined.

Conclusions

COVID-19-vaccinated individuals were strongly related to lower rates of ICU admission and in-hospital mortality throughout the dominance of the Delta and Omicron variants. Nevertheless, such an association was not present in unvaccinated individuals.

All evidence supported the undeniable fact that COVID-19 vaccination attenuates disease severity in hospitalized patients. Nevertheless, future research related to COVID-19 severity attenuation would require more comprehensive data from a prospective study design somewhat than electronic health record data.