Controversy Over 'Mulbaeksin' AZ... "Preventive Effect Drops Below 50% After 3 Months"
AZ Vaccination 3 Months Later, 47.3% Prevention Effect
"Sharp Decline Noted in Those Aged 65 and Over"
[Asia Economy Reporter Na Ye-eun] A study has found that the COVID-19 vaccine AstraZeneca (AZ) shows a rapid decline in effectiveness over time compared to other vaccines.
The UK Health Security Agency (UKHSA) conducted an experiment last month on individuals who had completed two doses of the AZ or Pfizer vaccines to observe the effects of an additional booster shot.
According to the report, the preventive effectiveness for AZ recipients was 62.7% at 1 week, rising to 66.7% between weeks 2 and 9. However, it began to drop to 59.3% at 10 weeks and fell further to 47.3% at 20 weeks. After 20 weeks post-vaccination, the infection prevention effectiveness dropped below 50%, which is the minimum threshold for emergency vaccine use authorization set by the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).
In contrast, the Pfizer vaccine started at 92.4% effectiveness at 1 week, decreased slightly to 89.8% from week 2, and showed a gradual decline to 80.3% after 10 weeks and 69.7% after 20 weeks.
For those aged 65 and older, the sharp decline in AZ’s preventive effectiveness was more pronounced. It recorded 63.8% at 1 week post-vaccination but dropped below 50% to 49.9% by week 10. After 20 weeks, the effectiveness was only 36.6%.
Pfizer’s effectiveness in the 65+ age group was also lower but remained higher than AZ, with 69.1% at 10 weeks and 55.3% at 20 weeks post-vaccination.
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Meanwhile, UKHSA stated that "after the additional booster shot, both vaccines’ preventive effectiveness rose above 90%." For individuals aged 50 and older who had received two doses of the AZ vaccine, an additional Pfizer booster increased infection prevention effectiveness to 93.1%. Those who had two doses of Pfizer also showed 94% effectiveness after the booster.
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