Omicron: A harbinger of the end of COVID-19 pandemic?

During the recent Omicron-driven wave of SARS-CoV-2 infection, there appears to be less severe COVID-19 disease compared with the previous wave driven by Delta, according to studies from South Africa — suggesting that Omicron may be a milder variant than its predecessors.

“A different pattern of characteristics and outcomes in patients hospitalized with COVID-19 was observed ... compared with earlier waves in South Africa, with younger patients having fewer comorbidities, fewer hospitalizations and respiratory diagnoses, and a decrease in severity and mortality,” researchers observed.

Based on data of 49 acute care hospitals in South Africa, 41.3 percent of patients who presented to the emergency department (ED) with a positive COVID-19 test during the early phase of Omicron-driven wave (mid-Nov to Dec 2021) were hospitalized compared with 68–69 percent of patients during the previous waves of infections. [JAMA 2021;doi:10.1001/jama.2021.24868]

Of note, the profile of patients being hospitalized was different than those in the Delta-driven wave, with the current ones being younger (median age, 36 years vs 59 years; p<0.001) with fewer comorbidities (23.3 percent vs 52.5 percent; p<0.001).

There were also fewer patients who had an acute respiratory condition (31.6 percent vs 91.2 percent; p<0.001), required oxygen therapy (17.6 percent vs 74 percent; p<0.001) or mechanical ventilation (1.6 percent vs 12.4 percent; p<0.001), and admission to intensive care unit (ICU; 18.5 percent vs 29.9 percent; p<0.001), compared with patients admitted during the Delta-driven wave.

In addition, the median length of hospital stay was shortened from 7–8 days to 3 days in the Delta- vs the Omicron-driven waves, respectively. About 2.7 percent of cases had died during the Omicron-driven wave compared with 29.7 percent during the Delta period.

“Further research is needed to determine if the differences between waves are affected by pre-existing acquired or natural immunity or if Omicron may be less pathogenic than previous variants,” the researchers stated.

Rapid surge and drop

Similar indications of decreased COVID-19 severity were also seen in another study comparing 466 COVID-19 hospitalizations from mid November 2021 onwards (driven by Omicron) vs 3,962 admissions during the period from 4 May 2020 till prior to the Omicron wave in the City of Tshwane, South Africa — the first global epicentre of the Omicron outbreak. [Int J Infect Dis 2021;116:38-42]

“The Omicron outbreak has spread and declined in the City of Tshwane with unprecedented speed, peaking within 4 weeks of its commencement,” said the researchers. “Hospital admissions increased rapidly and began to decline within a period of 33 days.”

Although the cases peaked rapidly, the peak bed occupancy rate during the Omicron wave was about half (51 percent) of the previous peak seen during the Delta wave — suggesting that fewer Omicron cases required hospitalization compared with the preceding wave.  

Even if the Omicron cases ended up being hospitalized, their length of stay was shorter compared with those admitted during the Delta wave (mean, 4.0 vs 8.8 days; p<0.00001).  

“The wave increased at a faster rate than previous waves, completely displacing the Delta variant within weeks and began its decline in both cases and hospital admissions in the fifth week following its commencement,” the researchers pointed out.

“This demonstrates a significantly different transmission trajectory and epidemiological profile from that of previous variants of concern,” they added.

The end of pandemic?

Despite the aggressive pace of surge in cases, there were fewer admissions to ICU (1 percent vs 4.3 percent; p<0.0007) and deaths (4.5 percent vs 21.3 percent; p<0.00001) during the Omicron vs the Delta waves.

“The death rate in the face of an exponential increase in cases during the Omicron wave … shows a decoupling of cases and deaths compared to previous waves, corroborating the clinical findings of decreased severity of disease seen in [hospitalized] patients,” the researchers suggested.

“There are clear signs that case and admission rates in South Africa may decline further over the next few weeks,” they noted. “If this pattern continues and is repeated globally, we are likely to see a complete decoupling of case and death rates, suggesting that Omicron may be a harbinger of the end of the epidemic phase of the COVID pandemic, ushering in its endemic phase.”