While it is becoming clear that the Omicron variant of Sars-CoV-2 is highly transmissible, many unresolved questions remain, according to a recent press briefing from the World Health Organization (WHO) in Geneva, Switzerland.

Among the unresolved issues is whether the variant causes milder or more severe disease, whether the risk of reinfection is greater with Omicron or other variants, and whether it is more transmissible than other variants such as Delta, according to WHO Director General Tedros Adhanom Ghebreyesus.

"Omicron is spreading at a rate we have not seen with any previous variant. We're concerned that people are dismissing Omicron as mild," Dr. Tedros said in mid-December at a briefing in Geneva. "Surely we have learned by now that we underestimate this virus at our peril. Even if Omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems."

In an earlier briefing, he noted, "Emerging data from South Africa increased risk of reinfection with Omicron, but more data are needed to draw firmer conclusions. There's also some evidence that Omicron causes milder disease than Delta, but again it's still too early to be definitive."

Dr. Tedros pointed out that that the Omicron variant has been reported in more than 50 countries and "we expect that number to continue growing. Certain features of Omicron, including its global spread and large number of mutations, suggest it could have a major impact on the course of the COVID19 pandemic."

He cautioned, however, "Exactly what that impact will be is still difficult to know. We are now starting to see a consistent picture of rapid increase in transmission, although for now the exact rate of increase relative to other variants remains difficult to quantify."

While conceding that the number of Omicron cases is increasing quickly in South Africa, Dr. Tedros advises, "However, Omicron was detected when transmission of Delta was very low, so it had little competition."

He also warns against making too many assumptions about Omicron. "New data are emerging every day, but scientists need time to complete studies and interpret the results. We must be careful about drawing firm conclusions until we have a more complete picture," he said.

He urged that actions be taken quickly to guard against COVID-19 mutation, stating, "Even though we still need answers to some crucial questions, we are not defenseless against Omicron, or Delta. The steps countries take today, and in the coming days and weeks will determine how Omicron unfolds."

"If countries wait until their hospitals start to fill up, it's too late," he warned, adding, "It will therefore be important to monitor carefully what happens around the world, to understand whether Omicron can outcompete Delta. For that reason, we call on all countries to increase surveillance, testing and sequencing. Our existing diagnostics work, both PCR and antigen-based rapid tests."

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