Herd immunity to be achieved when 70% of population is vaccinated

Korean government to roll out the AstraZeneca vaccine on Feb. 26 to residents and staff at senior care facilities

Health authorities set up a COVID-19 vaccination center in the Ajou University gymnasium in Suwon on Feb. 22. (Yonhap News)

Administering COVID-19 vaccines to over 70% of South Korea’s population will allow herd immunity to be achieved even when the virus’s reproduction number (R0, indicating the expected number of additional infections associated with any one patient) is around 2, the South Korean government said.

At the same time, it said the herd immunity target could be adjusted based on factors including the vaccine administration rate, vaccine supplies and infections with virus variants.

The government plans to begin administering a vaccine developed by AstraZeneca to residents and staff at long-term care hospitals and senior care facilities at 9 am on Feb. 26. Administration of the same vaccine to healthcare workers at middle-sized and large hospitals is to begin on Mar. 8.

In the daily briefing on Feb. 22, Korea Disease Control and Prevention Agency (KDCA) Commissioner Jung Eun-kyeong said, “If we assume an antibody formation rate of 80% following vaccination, then vaccination of 70% [of the population] would give a positive antibody rate of 56%.”

“Assuming a reproduction number of 2, we can come up with a simple estimate of around 50% being the standard for herd immunity,” she added. Her explanation came in response to pessimistic predictions that South Korea is unlikely to achieve herd immunity by November of this year by vaccinating 70% of the total population.

But Jung also noted, “The efficacy numbers for the vaccine could change with the numerous virus variants that have been emerging recently, and clinical testing [by the pharmaceutical companies responsible for developing vaccines] is currently being expanded to see whether the vaccine should be administered to those under the age of 18.”

“In light of these factors, there will need to be ongoing reviews and adjustments to our vaccination rate and herd immunity targets,” she said.

South Korea’s COVID-19 vaccinations are scheduled to begin at 9 am on Feb. 26. Around 289,000 residents and employees under the age of 65 at long-term care hospitals, senior care facilities, psychiatric hospitals and rehab facilities are set to receive the AstraZeneca vaccine.

On Feb. 27, administration of the Pfizer vaccine is to begin for healthcare workers treating COVID-19 patients. On Mar. 8, administration of the AstraZeneca vaccine is to begin for healthcare workers at medium-sized and large hospitals, which are frequently used by patients with severe symptoms.

By Suh Hye-mi, staff reporter

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