Data from the district at the heart of the Omicron variant wave in South Africa suggests the share of people developing severe illness or dying is significantly lower than in previous waves of coronavirus, although officials have warned the results are preliminary and that patterns may change as the wave spreads.

Data released on Friday by the country’s National Institute of Communicable Diseases shows that 31% of Covid-positive patients admitted to hospitals in the capital Pretoria in the past 25 days have required specialist care or spent time in intensive care, versus two-thirds of patients during the equivalent period of the second and third waves.

Mortality rates in hospital are also significantly lower at this stage. Four percent of Covid patients admitted in the past 25 days have died, up from 20 percent in the previous two waves.

Both sets of numbers are for patients whose hospital stay has ended, meaning that the numbers for the current wave will not be revised upwards due to the delay between admission and outcome.

The rates of severe illness and death were lower in patients in their 30s, 40s, 50s, 60s, 70s and 80s, suggesting that the lower severity model is not due to a difference in the age of Covid patients in the Omicron wave compared to other waves.

The results highlight reports from doctors in Pretoria that the level of care required by most patients in their Covid wards is lower than in previous waves.

“It should be noted that the severity data has several limitations at the start of a wave, where the numbers are low,” Joe Phaahla, South Africa’s health minister, said Friday in a briefing.

“This is the start, but there are promising signs that most patients, even those who are hospitalized, are mild and many of them are accidental,” he added.