By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: This study confirms the effectiveness of COVID-19 vaccination in preventing severe outcomes between the end of 2020 and October 2021 (i.e., pre-Omicron). Age, immunosuppression, and chronic disease were independent risk factors. In contrast to previous studies largely involving unvaccinated individuals, male sex and race/ethnicity were not.
SOURCE: Yek C, Warner S, Wiltz JL, et al. Risk factors for severe COVID-19 outcomes among persons aged ≥ 18 years who completed a primary COVID-19 vaccination series — 465 health care facilities, United States, December 2020–October 2021. MMWR Morb Mortal Wkly Rep 2022;71:19-25.
Yek and colleagues examined data from 465 U.S. facilities in the Premier Healthcare Database Special COVID-19 Release to evaluate protection from severe COVID-19 in individuals who had completed primary vaccination. The latter were defined as having received two doses of an mRNA vaccine or a single dose of the Johnson & Johnson (J&J) vaccine. A severe outcome was defined as any of the following: acute respiratory failure, requirement for noninvasive ventilation, intensive care unit (ICU) admission, or death.
Primary vaccination had been completed by 1,222,664 adults between December 2020 and October 2021, with > 90% receiving an mRNA vaccine. In total, 2,246 (18 per 10,000) developed COVID-19 and, of these, 327 required hospitalization, with 189 (1.5 per 10,000) having a severe outcome and 36 (0.3 per 10,000) having a COVID-19-related death. A comparison of outcomes of those who received the J&J vaccine and those who received the Pfizer-BioNTech product found no significant difference, but recipients of the Moderna vaccine had a lower adjusted odds ratio of a severe outcome (0.56; 95% confidence interval [CI], 0.32 to 0.98).
Of the 3,395 individuals who received an additional dose beyond their primary vaccination, COVID-19 occurred in 27 (0.8%), which was severe in three but did not result in ICU admission or death. None of 446 patients who received monoclonal antibody therapy (93% casirivimab/imdevimab) had a severe outcome.
Having a previous episode of COVID-19 was associated with a significantly reduced adjusted odds of a severe outcome (0.27; 95% CI, 0.09 to 0.84). On the other hand, the odds did not significantly differ by sex, race/ethnicity, time since primary vaccination, or becoming infected during the time when the Delta variant was predominant.
Independent risk factors for severe outcomes included age > 65 years, immunosuppression, diabetes mellitus, or chronic kidney, liver, neurologic, cardiac, or pulmonary disease. (See Figure 1.) All patients who had a severe outcome had at least one of these risk factors, and 78% of those who died had at least four of them.
Figure 1: Frequency of Risk Factors in Persons with COVID-19 After Completion of a Primary Vaccination Series, by Outcome*,† — 465 Healthcare Facilities, United States, December 2020–October 2021 |
ICU: intensive care unit * Outcome totals: nonsevere = 2,057; ICU/respiratory failure = 153; deaths = 36. † All persons in the ICU or respiratory failure (survivors) and deceased groups had at least one risk factor Source: Yek C, Warner S, Wiltz JL, et al. Risk factors for severe COVID-19 outcomes among persons aged |
COMMENTARY
This very large study documents the efficacy of the vaccines used in the United States, although the period of study antedates the emergence of the Omicron variant, against which the protective effect appears to be diminished. The identified risk factors for serious outcomes largely track with previous studies, which were, however, mostly performed prior to the availability of vaccination. Some significant differences from those study results did emerge. Thus, an increased risk among males was not identified nor was race/ethnicity found to be a risk factor — suggesting that vaccination can overcome whatever increased risk is present in these groups.
However, one difference from other studies of vaccinated individuals was the lack of effect of the interval between vaccination and the occurrence of severe outcomes. Since vaccine studies have found a clear diminution of protection largely beginning five to six months after vaccination, this would appear to be paradoxical. However, the interval category that was the longest examined began at four months, possibly diluting an interval effect. At any rate, the current recommendation for booster doses starting five months after primary vaccination should provide significant benefit.
The authors rightly indicated that these findings provide a basis for public health interventions that include improved management of chronic diseases, reducing exposure to SARS-CoV-2, and increasing the proportion of the population that has received primary and booster vaccinations. They also provide data allowing more targeted interventions, such as the use of monoclonal antibodies, in symptomatically infected outpatients.
This study confirms the effectiveness of COVID-19 vaccination in preventing severe outcomes between the end of 2020 and October 2021 (i.e., pre-omicron). Age, immunosuppression, and chronic disease were independent risk factors. In contrast to previous studies largely involving unvaccinated individuals, male sex and race/ethnicity were not.
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