Omicron Transmission, Up to 8 Days After Symptom Onset... "Vaccination Reduces Transmission"

Stealth Omicron Share at 26.3%
No Significant Difference from Other Omicron Variants

[Asia Economy Reporter Ki Ha-young] The period during which the virus spreads after Omicron infection has been found to be up to 8 days after symptom onset. Additionally, the domestic prevalence of BA.2, known as the 'Stealth Omicron,' has increased to 26.3%, indicating its spread.

The Central Disease Control Headquarters announced on the 17th the results of a study investigating the infectious virus shedding period to confirm the possibility of virus transmission from confirmed Omicron variant cases.

Omicron Transmission Period: Up to 8 Days After Symptom Onset

Investigating a total of 558 specimens within 14 days after symptom onset (281 vaccinated cases, 277 unvaccinated cases), the maximum period during which infectious virus is shed was found to be 8 days after symptom onset. The vaccinated group includes those who received the 2nd and 3rd doses, while the unvaccinated group includes unvaccinated individuals and those who received only the 1st dose.

In particular, it was confirmed that the virus transmission potential of vaccinated individuals is lower compared to unvaccinated individuals. During the study period, the culture positivity rate in the unvaccinated group was 53%, which was statistically significantly higher by 1.56 times compared to the 34% positivity rate in the vaccinated group. Although there was no difference in the duration of virus shedding at an infectious level, the vaccinated group showed reduced shedding of infectious virus at the same virus concentration level.

The health authorities explained, "These results indicate that the possibility of virus transmission in vaccinated individuals is reduced compared to unvaccinated individuals due to the effect of vaccination," adding, "Vaccination is necessary because it lowers the virus infectivity and reduces the possibility of transmission."

The Central Disease Control Headquarters plans to announce these research results publicly and share them with domestic and international researchers.

Stealth Omicron Prevalence at 26.3%

The domestic prevalence of BA.2, a sub-lineage of Omicron known as Stealth Omicron, is also increasing. According to the Central Disease Control Headquarters, the prevalence of BA.2 in the second week of March was 26.3%, showing a gradual increase from 1.5% in January and 17.3% in February.

According to initial analyses by the World Health Organization (WHO) and overseas health agencies, BA.2 shows 30% higher transmissibility than BA.1, but there is little difference in clinical severity and hospitalization rates between BA.1 and BA.2. There are effective antibody treatments for BA.2, and antiviral drugs remain effective as with other major variants. The preventive effect after the 3rd booster vaccination (mRNA) is also known to be similarly effective against both BA.1 and BA.2.

Considering the decline in epidemic trends in countries with high BA.2 proportions such as Denmark and the global decrease in case numbers, WHO judges that the somewhat increased transmissibility of BA.2 is unlikely to have a significant impact on the rise in confirmed cases.

However, health authorities are monitoring the situation with caution, noting that BA.2 shows a high prevalence in countries like the UK and Germany where confirmed cases have recently increased, and that the domestic prevalence of BA.2 is also on the rise, potentially influencing case increases. Notably, Korea’s PCR tests have been designed from the start to detect BA.2, so there is no issue in identifying BA.2. Although the BA.2 variant is nicknamed 'Stealth Omicron' because it is harder to detect target genes in PCR tests compared to the general Omicron BA.1, health authorities explain that this nickname itself may cause excessive fear.

Lee Sang-won, head of the Epidemiological Investigation and Analysis Division at the Central Disease Control Headquarters, said, "BA.2 is about 30% more infectious than BA.1 and has a shorter transmission period, causing more frequent spread, but there is no significant difference in its nature, and reinfections are not prominent in other countries either. While vigilance is necessary, there is no need for excessive concern."

This content was produced with the assistance of AI translation services.