Vaccine-induced or hybrid immunity and COVID-19-associated mortality during the Omicron wave

Comparison of fatalities due to COVID-19 and other nonexternal causes during the first five pandemic waves : Results from multiple cause of death statistics in Bavaria

BACKGROUND

Older age is a risk factor for a fatal course of SARS-CoV‑2 infection, possibly due to comorbidities whose exact role in this context, however, is not yet well understood. In this paper, the characteristics and comorbidities of persons who had died of COVID-19 in Bavaria by July 2022 are shown and compared with the characteristics of other fatalities during the pandemic.

METHODS

Based on data from multiple cause of death statistics, odds ratios for dying from COVID-19 (compared to dying from other nonexternal causes of death) were calculated by using logistic regression models, stratified by age, sex, and pandemic waves.

RESULTS

In Bavaria, a total of 24,479 persons (6.5% of all deaths) officially died from COVID-19 between March 2020 and July 2022. In addition to increasing age and male sex, preexisting diseases and comorbidities such as obesity, degenerative diseases of the nervous system, dementia, renal insufficiency, chronic lower respiratory diseases, and diabetes mellitus were significantly associated with COVID-19-related deaths. Dementia was mainly associated with increased COVID-19 mortality during the first and second waves, while obesity was strongly associated during the fourth wave.

DISCUSSION

The frequency of specific comorbidities in COVID-19 deaths varied over the course of the pandemic. This suggests that wave-specific results also need to be interpreted against the background of circulating virus variants, changing immunisation levels, and nonpharmaceutical interventions in place at the time.

Long-Term Trends in the Protection Against Severe Courses of COVID-19 by Vaccination

BACKGROUND

The long-term course of protection against severe COVID-19 courses by vaccine-induced or hybrid immunity in Germany is unclear.

METHODS

We studied 146 457 cases aged 60-99 years in the German federal state of Bavaria who were immunized against COVID-19 and tested positive for it from February 2022 to January 2023. We calculated adjusted hazard ratios for a severe course (hospitalization or death due to COVID-19) for different intervals between the onset of full primary or booster immunity and the date of the infection.

RESULTS

3342 (2.3%) severe courses of COVID-19 were observed in the first 60 days after the infection. The risk of a severe course rose with the interval between the onset of immune protection and the infection (adjusted hazard ratios and 95% confidence intervals at 6, 9, 12, and 15 months: 1.14 [1.08; 1.20]; 1.33 [1.24; 1.42]; 1.39 [1.25; 1.54]; 1.61 [1.35; 1.93]). The risk rose more slowly when mRNA-based vaccines were used exclusively. In a previous study, we observed 82% initial efficacy in cases aged 60 and above who received a booster vaccination (compared to unvaccinated cases) and an absolute risk reduction of 2.1%. If one extrapolates these findings to the current study, the residual efficacy and absolute risk reduction are found to be approximately 71% and 1.8% (respectively) at 6 months, and 32% and 0.8% at 15 months.

CONCLUSION

These results indicate that, during the Omicron wave, the protection of older persons against a severe COVID-19 course gradually declined from six months after vaccination onward. The limitations of this study include confounders that could not be taken into account, possible misclassification of the cause of death, and selection bias due to missing information about vaccination status and severe COVID-19 courses.