The First Case of a Child Infected with SARS-CoV-2 Omicron Variant in Japan, December 2021.

We report the first pediatric patient infected with the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Japan. The patient was a one-year-old boy who resided in Japan. He went abroad with his parents from November 12, 2021 to November 28, 2021 and had no known contact with coronavirus disease (COVID-19) patients there. Upon arrival at the Narita International Airport on November 28, 2021, his father tested positive for SARS-CoV-2 via a quantitative antigen test. Because the boy and his mother tested negative for SARS-CoV-2, they quarantined together at a hotel separately from his father. On December 4, 2021, the boy tested positive by reverse-transcription polymerase chain reaction (RT-PCR) for SARS-CoV-2, without symptoms, and was hospitalized with his mother; he and his father were both found to be infected with the SARS-CoV-2 Omicron variant. The boy was not vaccinated against COVID-19. RT-PCR results were negative starting on December 20, 2021. The incubation period and required period for negative conversion of SARS-CoV-2 RNA of the Omicron variant case were similar to those of the cases of conventional strains. We should carefully consider the potential of the SARS-CoV-2 Omicron variant to spread widely among unvaccinated children.