COVID-19 Winter Resurgence Shifts to 'Increasing Trend'... Spread Speed of New Variant BN.1 Is Key

Weekly New Cases Increase by 11.2%... Infection Reproduction Number Above 1 for 8 Consecutive Weeks
Reinfections Twice or More Up 13% from Previous Week... 1 in 7 Cases Are Reinfections
BN.1 Detection Rate Exceeds 17%, Influencing Rise in Confirmed Cases

As the number of new COVID-19 cases increases and the reinfection rate rises, the winter resurgence has returned to an upward trend. Additionally, the detection rate of the BN.1 variant, a subvariant of Omicron, is on the rise, emerging as a key factor in estimating the future scale of the outbreak.

According to the Central Disease Control Headquarters on the 15th, the number of new COVID-19 cases in the first week of December was 412,707 over the week, an increase of 41,645 (11.2%) from 371,065 the previous week. This is also 68,498 (19.9%) more than the 344,209 cases reported in the second week of November, four weeks earlier.

The effective reproduction number (Rt) was 1.04, maintaining a level above 1 for eight consecutive weeks. An Rt above 1 indicates 'epidemic expansion.' The incidence rate increased across all age groups compared to the previous week, with significant rises among school-age children, young adults, and the elderly aged 80 and above. The average daily number of critically ill COVID-19 patients hospitalized was 444, a 4.9% decrease from the previous week, while deaths increased by 6.2% to 51 per day.

As of the last week of November, the estimated proportion of reinfection cases was 14.7%, up 1.41 percentage points from 13.29% the previous week. This means that one in seven new confirmed cases was infected two or more times. Among the total cumulative infected individuals, 3.1% had been infected two or more times.

Im Suk-young, the Situation General Manager of the Central Disease Control Headquarters, stated in a briefing the day before, "With the onset of significant temperature drops, increased indoor activities during the year-end and New Year holidays, and declining immunity levels, the number of confirmed cases, which had temporarily slowed, is rising again," adding, "The current outbreak is gradually increasing while fluctuating."

In particular, among the Omicron subvariants, the detection rate of BA.5 and its sublineages (BF.7, BQ.1, BQ.1.1) remains dominant at 71.3%, while the detection rate of the BN.1 variant has recently been increasing. BN.1, also known as the 'Centaurus variant,' is a sublineage of Omicron BA.2.75. It was previously called 'BA.2.75.5.1' but was renamed 'BN.1' starting in September.

In South Korea, since its first detection on September 22, the detection rate of BN.1 has rapidly increased over four weeks from 7.6% to 7.7%, then 13.2%, and 17.4%. Among imported cases, 24.2% were BN.1, and as overseas arrivals increase, domestic infections are also following this trend.

Im said, "Even though BN.1 is increasing, the speed is quite gradual," adding, "Looking at cases in the U.S. and Europe, the increase rate is lower compared to BQ.1 or BQ.1.1, so it is judged that the spread speed will not be as fast as the existing BA.5." However, Im added, "As the share of BN.1 continues to rise, it will have a certain impact on the winter COVID-19 outbreak. We will closely monitor these developments."

Hwang Kyung-won, Vaccination Planning Team Leader of the COVID-19 Vaccination Response Promotion Team, predicted, "Since BN.1 is also an Omicron variant, the currently administered bivalent vaccines are expected to be sufficiently effective." Im emphasized, "It has been confirmed that receiving an additional bivalent booster vaccine, specialized for the currently circulating Omicron variants, reduces the risk of infection by nearly half compared to those who only completed the primary vaccination series," and stressed, "Vaccination is paramount to safely overcoming the winter resurgence without uniform social distancing measures."