The Impact of Vaccination on Severity of Illness in COVID-19

With the FDA's emergency use authorization declaration in December of 2020, the Pfizer-BioNtech vaccine became the first of several vaccines to kick off the mass vaccination effort across the United States against CoronaVIrus Disease 2019 (COVID-19). Subsequently, Moderna as well as Johnson and Johnson both had vaccines receive emergency use authorization. While the Pfizer and the Moderna vaccines both utilize novel mRNA technology, Johnson and Johnson's vaccine uses a viral vector that has been used previously in both the approved European Ebola vaccine and a trial vaccine for HIV. However, none of these vaccine types have previously been approved in the United States. While preliminary data from safety and efficacy trials have shown positive results, actual-world data on its effectiveness is still lacking. Several small cohort studies and one large trial from Israel are currently the only insights into the actual rates of infection, hospitalization, and severe illness among vaccinated individuals. As COVID-19 variants, with the potential to reduce vaccine efficacy, continue to emerge worldwide, there is a need of more data regarding the real-world effectiveness of our current mass vaccination efforts.

Vaccination efforts in the State of Michigan have been ongoing since December 2020. Given that approximately 33.7% of the state's population is either partially or fully vaccinated, it is unclear why the number of cases has risen so dramatically or if immunization efforts can help the situation.

Given the current situation in the State of Michigan, this study will evaluate the efficacy of COVID-19 vaccination on rates of hospital visits and severe illness when breakthrough Severe Acute Respiratory Syndrome coronavirus-2 (SARS-CoV-2) infection occurs in a region with high incidence of variant strain disease.

A retrospective chart review of all patients presenting to Beaumont Health System emergency departments between December 15, 2020 and April 30, 2021 who tested positive for COVID-19 will be performed. The primary aim is to compare the rate of Emergency Department (ED) presentations/hospitalizations among unvaccinated, partially vaccinated, and fully vaccinated patients presenting to an emergency center (EC). Secondarily, the rates of individual clinical outcomes of COVID-19 infection for hospitalized patients will be compared among unvaccinated, partially vaccinated, and fully vaccinated patients, including the proportion of COVID-positive patients who develop severe disease, require admission to the hospital, and rates of those requiring intensive care unit (ICU) admission, mechanical ventilation, extracorporeal membrane oxygenation (ECMO), renal replacement therapy (RRT), supplemental oxygenation, or noninvasive ventilation, as well as the rate of in-hospital mortality and the hospital length of stay. Exploratory outcomes may include comparisons among fully-vaccinated individuals receiving each of the three types of vaccines, and investigation of demographic, epidemiological, clinical and laboratory predictors of hospitalization. For each individual, data collected will include vital signs (temperature, blood pressure, heart rate, respiratory rate, pulse oximetry), demographics (age, gender, existing medical conditions), home medications, chief complaint from emergency provider note, duration of symptoms in days at the time of presentation from emergency provider note, chest X-ray or chest computed tomography (CT) results, and laboratory values. For patients who were admitted, data collected will include initial hospital admission unit (regular medical or surgical floor, progressive floor, intensive care unit), change in unit type during admission, oxygen therapy (none, nasal cannula, supplemental high flow oxygen, ventilator), days on high flow oxygen, days on ventilator, specific inpatient medical therapies, laboratory values, imaging results, hospital length of stay, and disposition from hospital (home, rehabilitation unit, death).

Eligibility Criteria:
Inclusion Criteria:

* All patients presenting to Beaumont Health emergency departments who have tested positive for COVID-19 between December 15, 2020 and April 30, 2021 with available vaccination data through state of Michigan registry.

Exclusion Criteria:

* Patients who have previously tested positive for COVID-19 prior to the study period will be excluded.
* Patients with missing vaccine status will be excluded.