At least 5 days required to confirm omicron infection

The Yomiuri Shimbun

15:20 JST, January 6, 2022

Five to seven days are needed to confirm infection with the omicron variant of the coronavirus, due to a three-step process based on a notice from the Health, Labor and Welfare Ministry.

The three steps comprise a PCR or antigen test to confirm if an examinee is infected with the coronavirus; another PCR test to check if they have the currently prevalent delta variant; and finally, genome analysis to confirm if they are infected with omicron.

The first test is carried out at medical facilities and elsewhere. A PCR test takes between one to four hours, and an antigen test about 30 minutes, to get a result. If the tests are administered by a private company, this stage takes about a day.

Prefectural governments are primarily responsible for the second step. The delta and omicron variants differ as to where the virus has mutated, and a PCR test checks for mutations specific to delta. If no mutation is found at this stage, examinees are suspected to be infected with omicron, as it is currently rampant. It takes at least a day to transport and test a specimen.

Genome analysis is performed if omicron is suspected. This checks all the genetic information of the virus and takes about three days to get a result.

Altogether, the process involves at least five days.

The Tokyo metropolitan government has developed an original PCR test that can detect characteristics of omicron in the second step, and has conducted it since December last year at the Tokyo Metropolitan Institute of Public Health in Shinjuku Ward.

About 100 people can be checked daily, with results available in about 24 hours. In this process as well, genome analysis is performed as the final step. In Tokyo, 72 omicron cases had been confirmed by Wednesday.

The health ministry has asked prefectural governments to perform genome analysis on suspected omicron infections to the greatest extent possible, to monitor the shift from delta to omicron as the dominant variant.

Once omicron is confirmed to have become dominant, the system of genome analysis will be reconsidered.