In a recent study published in the Morbidity and Mortality Weekly Report, a team of researchers from the United States (US) performed a case-control study to evaluate the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) messenger ribonucleic acid (mRNA) vaccines.
The researchers measured the efficacy of mRNA vaccines against coronavirus disease 2019 (COVID-19)-induced invasive mechanical ventilation (IMV) and in-hospital mortality in adult patients.
In the US, almost 1 million SARS-CoV-2-related deaths have occurred as of March 2022, predominantly in unvaccinated patients. SARS-CoV-2 mRNA vaccines - Pfizer-BioNTech BNT162b2 and Moderna mRNA-1273 - were effective in ameliorating COVID-19-associated hospitalizations, life-threatening outcomes, and deaths. However, the efficacy of mRNA vaccines to protect against COVID-19-associated most severe complications or hospitalizations including use of IMV or death is unknown.
In this study, the researchers considered previous COVID-19 vaccination status (two or three doses) in COVID-19 case-patients who were on IMV or those who died within 28 days of hospitalization and compared with COVID-19-negative control hospitalized patients.
In this study, the authors included adult patients hospitalized at 21 US medical centers between 11 March, 2021, to 24 January, 2022. Surveillance data for this case-control study was collected from influenza and other viruses in the acutely ill (IVY) network. Case-patients included hospitalized adults with COVID-19-related illness and who tested SARS-CoV-2 positive through nucleic acid amplification test (NAAT). The enrolment of the case-patients included only those who have received IMV or died. While control patients included hospitalized adult patients with or without SARS-CoV-2-associated illness and a negative NAAT test.
COVID-19 vaccination status was retrieved from hospital electronic medical records, state registry data, record cards for vaccination, and self-reports. Pearson’s chi-square for categorical variables compared demographic and clinical features between vaccinated and unvaccinated COVID-19 case-patients. Logistic regression calculated vaccine effectiveness (VE) by comparing previous mRNA vaccination odds (two or three doses) in COVID-19-case patients exposed with IMV or death in hospital as compared to control patients.
The variant dominant period was determined by using whole-genome sequencing of samples collected in the IVY network. The authors performed an additional sensitivity analysis by restriction of COVID-19 negative controls with those who have received IMV or died within 28 days of admission.
The findings of the study demonstrated that among the patients studied, 19% were COVID-19 case-patients exposed to IMV, mortality, or both and 81% were negative controls.
Vaccinated case-patients were older (median age 69) as compared to unvaccinated case-patients (median age 55). Further 11% vaccinated case-patients had more probability to live in a long-term facility compared to 2% unvaccinated case-patients. Around 44% of vaccinated case-patients had more probability of hospitalization in the previous year compared to 22% unvaccinated patients and 40% of the vaccinated patients were likely to have immunocompromised conditions compared to 10% unvaccinated patients.
The findings of the study demonstrated that across the surveillance period, mRNA vaccine showed 90% VE against COVID-19-related IMV or mortality. This was similar to 91% VE for IMV only and 88% in-hospital death. Moreover, in COVID-19 test-negative control patients, the mRNA vaccine showed 86% VE for patients with IMV or those who died.
Over the entire study duration, recipients who received the second vaccination dose showed 92% VE post 14-150 days of second dose administration and 84% VE at more than 150 days post-vaccination.
Notably, among recipients administered with three vaccine doses, VE was 94%. In immunocompetent adults, VE for two or three vaccine doses was 98%. Intriguingly, VE was 74% (lowest) in immunocompromised patients. During the SARS-CoV-2 Omicron surge, VE for IMV or in-hospital mortality, for two and three vaccine dose recipients were 79% and 94%, respectively.
The findings of the study demonstrated that the administration of two or three doses of COVID-19 mRNA vaccine in adults elicited 90% overall protection against COVID-19-related IMV or deaths. The majority of vaccinated patients who developed COVID-19-related IMV or died in hospital were elderly population with underlying immunosuppression conditions.
The study confirmed the highly protective efficacy of mRNA COVID-19 vaccines against severe complications and deaths by different SARS-CoV-2 variants in the adult population. The authors highly recommended vaccination of all eligible persons and stressed staying up to date with current information regarding COVID-19 vaccination.