Effect of vaccination on the case fatality rate for COVID-19 infections 2020–2021: multivariate modelling of data from the US Department of Veterans Affairs

Abstract

ObjectivesTo evaluate the benefits of vaccination on the case fatality rate (CFR) for COVID-19 infections.Design, setting and participantsThe US Department of Veterans Affairs has 130 medical centres. We created multivariate models from these data—339 772 patients with COVID-19—as of 30 September 2021.Outcome measuresThe primary outcome for all models was death within 60 days of the diagnosis. Logistic regression was used to derive adjusted ORs for vaccination and infection with Delta versus earlier variants. Models were adjusted for confounding factors, including demographics, comorbidity indices and novel parameters representing prior diagnoses, vital signs/baseline laboratory tests and outpatient treatments. Patients with a Delta infection were divided into eight cohorts based on the time from vaccination to diagnosis. A common model was used to estimate the odds of death associated with vaccination for each cohort relative to that of unvaccinated patients.Results9.1% of subjects were vaccinated. 21.5% had the Delta variant. 18 120 patients (5.33%) died within 60 days of their diagnoses. The adjusted OR for a Delta infection was 1.87±0.05, which corresponds to a relative risk (RR) of 1.78. The overall adjusted OR for prior vaccination was 0.280±0.011 corresponding to an RR of 0.291. Raw CFR rose steadily after 10–14 weeks. The OR for vaccination remained stable for 10–34 weeks.ConclusionsOur CFR model controls for the severity of confounding factors and priority of vaccination, rather than solely using the presence of comorbidities. Our results confirm that Delta was more lethal than earlier variants and that vaccination is an effective means of preventing death. After adjusting for major selection biases, we found no evidence that the benefits of vaccination on CFR declined over 34 weeks. We suggest that this model can be used to evaluate vaccines designed for emerging variants.

Changes in Outpatient Health Care Use After COVID-19 Infection Among Veterans

“…Sustained higher outpatient use may be due to patients with PCC, which merits exploration in future work and has potential implications for VA workforce planning. Third, subgroup analyses found that the short-term visit increase following COVID-19 infection was greater for older veterans, veterans with a high comorbidity burden, Hispanic veterans, rural veterans, and veterans who were not vaccinated . Improved access to telehealth for these more vulnerable veterans may benefit them and their caregivers, if telehealth obviates the need for caregivers to provide veterans with travel for care.…”

“…Veteran characteristics were chosen for subgroup analyses according to differences reported in the clinical severity of COVID-19 infection, 26 , 27 , 28 including age groups (20-44, 45-54, 55-64, 65-74, 75-84, and ≥85 years), sex, self-reported race, self-reported Hispanic ethnicity, smoking status, immunosuppression at index date, vaccination status at index date, rural or urban residence, comorbidity burden (defined as Gagne score 29 quartiles), and the pandemic wave in which the infection occurred. 30 Race and ethnicity in the VA Corporate Data Warehouse are collected through self-identification either at enrollment or at a health care encounter and are included in this study for descriptive purposes and because outpatient visits are known to vary by race and ethnicity.…”