Background:
In late 2021, the wave of the B.1.1.529 SARS-CoV-2 (Omicron) variant replaced the wave of the B.1.617.2 (Delta) variant.
Aim:
To compare baseline characteristics and in-hospital outcomes of patients with SARS-CoV-2 infection with the Delta variant versus the Omicron variant in the emergency department (ED).
Design:
Retrospective chart reviews.
Locations:
13 adult emergencies in academic hospitals in the Paris area from November 29, 2021 to January 10, 2022.
Patients:
Patients with a positive reverse transcription-polymerase chain reaction (RT-PCR) test result for SARS-CoV-2 and variant identification.
Measurements:
The main outcome measures were baseline clinical and biological characteristics at presentation to the emergency department, intensive care unit (ICU) admission, mechanical ventilation, and in-hospital mortality.
Results:
A total of 3728 patients had a positive RT-PCR test result for SARS-CoV-2 during the study period; 1716 patients who had a variant determination were included (818 Delta and 898 Omicron).
The median age was 58 years and 49% were women.
Omicron : Patients infected with the Omicron variant were younger (54 vs. 62 years; difference, 8.0 years [95% CI, 4.6 to 11.4 years]), had a lower rate of obesity ( 8.0% vs. 12.5%; difference, 4.5 percentage points [CI, 1.5 to 7.5 percentage points]), were more vaccinated (65% vs. 39% for 1 dose and 22% vs. . 11% for 3 doses), had a lower rate of dyspnea (26% vs. 50%; difference, 23.6 percentage points [CI, 19.0 to 28.2 percentage points]), and had a higher rate of discharge home from the emergency department (59% vs. 37%; difference, 21.9 percentage points [−26.5 to −17.1 percentage points]).
Compared with Delta, Omicron infection was independently associated with a lower risk of ICU admission (adjusted difference, 11.4 percentage points [CI, 8.4 to 14.4 percentage points]), mechanical ventilation ( adjusted difference, 3.6 percentage points [CI, 1.7 to 5.6 percentage points]) and in-hospital mortality (adjusted difference, 4.2 percentage points [CI, 2.0 to 6.5 percentage points] ).
Limitation:
Patients with COVID-19 disease and without SARS-CoV-2 variant determination in the emergency department were excluded.
Conclusion:
Compared with the Delta variant, infection with the Omicron variant in patients in the emergency department had different clinical and biological patterns and was associated with better in-hospital outcomes, including improved survival.
Discussion
In this retrospective chart review of 1,716 patients who visited an academic ED in the Paris area and a variant was identified, 52% were infected with Omicron and 48% were infected with Delta.
Omicron affected a younger population, with a higher rate of vaccination, a lower rate of respiratory symptoms, reduced levels of inflammation, and less extensive chest involvement on CT scan. Adjusted analysis reported that Omicron was independently associated with improved hospital outcomes.
Since November 2021 and the first identification of the Omicron variant in South Africa, studies have reported that this variant is more infectious and that immune escape leads to lower vaccine effectiveness. The current study confirms these findings, with a higher proportion of vaccinated patients among those infected with Omicron, as also observed by Brandal and colleagues in Denmark.
Another interesting finding was that the time from symptom onset to emergency department visit was shorter in patients on Omicron compared to those on Delta. This may be related to the fact that Omicron appears to have a tropism for the upper respiratory tract rather than the lower respiratory tract, which is also seen in cases of other respiratory viruses, including other coronaviruses.
Symptoms may develop more rapidly in the upper respiratory tract than in the lower respiratory tract, and therefore the time from first symptoms to decompensation requiring an emergency department visit is shorter for Omicron than for Delta.
Some other hypotheses can also be put forward and will require further exploration, such as a faster replication rate or an earlier immune response among vaccinated patients infected more frequently with Omicron than with Delta. However, a post hoc analysis reported no association between the number of vaccine doses and mean symptom delay for Omicron or Delta.
| In conclusion , patients who attended the emergency room with SARS-CoV-2 infection presented different clinical characteristics when they were infected with the Omicron variant compared to the Delta variant, with a younger age, fewer respiratory symptoms and a lower inflammatory response. Compared with Delta, Omicron infection was independently associated with lower risks of ICU admission, mechanical ventilation, and in-hospital death. |
