Omicron's spread, severity: 2 new findings

New findings about omicron's spread and severity are emerging daily, with recent research pointing to a higher rate of asymptomatic spread and lower hospitalization risk.

Below is a summary of recent study findings. 

On omicron's spread:

Omicron has a much higher rate of asymptomatic spread than other variants, according to early findings published Dec. 27 by preprint server MedRxiv. Researchers evaluated asymptomatic carriage in a vaccine trial for South African healthcare workers, which indicated 2.6 percent asymptomatic carriage during the beta and delta outbreaks and 16 percent asymptomatic carriage during the omicron period. 

Another study conducted by the same researchers in December showed 31 percent asymptomatic carriage among 230 participants. The study found similar asymptomatic carriage rates in individuals who had had COVID-19 before and those who had not. The findings strongly suggest that omicron's high prevalence of asymptomatic infection is likely a major factor in the rapid spread of the virus, even among populations with high rates of prior infection. The data is "in stark contrast to COVID-19 vaccine studies conducted pre-omicron," according to the study authors. The study has not been peer reviewed.

On omicron's severity:

A separate study involving nearly 70,000 COVID-19 patients at Kaiser Permanente of Southern California found patients with omicron infections were less likely to be hospitalized for COVID-19, and when they were, they had shorter hospital stays.

For the study, published Jan. 11 in MedRxiv, researchers from Kaiser and the CDC analyzed EHR data on 69,279 COVID-19 patients treated between Nov. 30, 2021, and Jan. 1, 2022. About 52,000 patients had omicron infections, and nearly 17,000 had delta infections. 

Patients with omicron infections were half as likely to require hospitalization, researchers found. Just 0.5 percent of omicron patients were hospitalized, compared to 1.3 percent of those with delta infections. Of those hospitalized with omicron, none were put on ventilators. 

"It's truly a viral factor that accounts for reduced severity," study author Joseph Lewnard, PhD, an epidemiologist at the University of California-Berkeley, told The New York Times.

The median hospital stay was also 3.4 days shorter for patients with omicron compared to patients with delta. The study has not been peer reviewed.


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