"Pfizer's Effectiveness Declines Over Time Compared to AZ... Prevention Effectiveness to Decrease Soon"

On the 21st, medical staff are administering COVID-19 vaccines at the vaccination center set up in the Health Healing Culture Center in Yangcheon-gu, Seoul. [Image source=Yonhap News]

[Asia Economy Reporter Kim Soyoung] A foreign study has found that the sustained effectiveness of the Pfizer COVID-19 vaccine declines faster than that of the AstraZeneca (AZ) vaccine. However, despite this decrease, Pfizer showed greater preventive effectiveness up to three months after vaccination. The researchers predicted that after 4 to 5 months, the AZ vaccine would demonstrate higher preventive effectiveness than Pfizer.

On the 20th (local time), British media including the Financial Times (FT) and The Independent reported, citing a study from Oxford University, that while the Pfizer vaccine is stronger against the Delta variant than the AZ vaccine, its sustained effectiveness is shorter.

Initially, Pfizer's preventive effectiveness is higher, but the rate of decline afterward is relatively greater. For this reason, the researchers added that after 4 to 5 months post-vaccination, AZ might have higher preventive effectiveness.

However, experts emphasized that regardless of the duration of preventive effectiveness, any vaccine significantly reduces the risk of COVID-19 through vaccination.

According to the research team's analysis, the preventive effectiveness one month after the second dose of the Pfizer vaccine was over 90% higher compared to unvaccinated individuals. After two months, it was 85%, and after three months, it gradually decreased to 78%. During the same period, the AZ vaccine showed steady preventive effectiveness of 67%, 65%, and 61%, respectively, the researchers stated.

The current study was conducted only up to three months after vaccination completion, but based on the data so far (trend of effectiveness decline), the researchers estimated that after 4 to 5 months post-vaccination, AZ might show higher preventive effectiveness compared to Pfizer.

Additionally, the research team noted that both vaccines have reduced preventive effectiveness against the Delta variant compared to the Alpha variant, and that even fully vaccinated individuals may transmit the Delta variant.

Dr. Coen Powles of Oxford University emphasized, "Even if the (vaccine) preventive effectiveness decreases somewhat, it is important to remember that overall vaccine effectiveness remains very high."

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