JOHANNESBURG, (Reuters) – Preliminary results from South African clinical trials indicate that Omicron coronavirus variants have a higher rate of “asymptomatic transmission” than other variants. This could help explain its rapid spread across the globe.

One study was done when Omicron infected were raging in South Africa, while another resampled participants at the same time. Both studies found that more people had tested positive for the coronavirus and were showing no symptoms.

Ubuntu Study evaluating efficacy Moderna (31% of 230 HIV patients were screened for COVID-19, and the results from all 56 samples that could be sequenced have been confirmed as Omicron.

Researchers stated in a statement that “This contrasts starkly with the positivity rate pre Omicron which varied from less than 1 to 2 percent.”

In a subgroup of the Sisonke trial evaluating the efficacy of Johnson & Johnson (NYSE:)’s COVID-19 vaccine, the mean asymptomatic carriage rate rose to 16% during the Omicron period from 2.6% during the Beta and Delta outbreaks.

Researchers stated, “The Sisonke research included 577 subjects who were previously vaccinated… and the results suggest a high prevalence even for those already vaccinated.”

The researchers also stated that the faster and more widespread spread of the variant was likely due to the higher asymptomatic carrier rate, even in populations with low prior coronavirus infections.

South Africa saw a spike in COVID-19 infection rates from November to the point when its scientists alerted Omicron. New cases of COVID-19 infections have declined since then, and the early signs suggest that there has been less serious diseases than in previous waves.