In addition to broad global access to vaccines for everyone, booster vaccinations have the potential to play an important role in the fight against COVID-19. However, debates around booster shots of COVID-19 vaccines continue in the news and social media. Booster shots are needed because the protection from the original two doses of vaccine wanes over time. This happened as the Delta variant became more prominent around the world. Until now, there has been very limited clinical research information about the effectiveness of booster doses.

Results from first randomized controlled trial

New early data suggests that a booster dose of the Pfizer vaccine is 95.6% effective against COVID-19. This is compared to just two shots of the Pfizer vaccine and also compared to a placebo (dummy shot that looks just like the real shot but does not contain the vaccine). In this study with 10,000 participants who had all gotten two shots of the Pfizer vaccine, half were given a third equal-strength dose of the vaccine, and half were given a placebo. The age of participants was around 53 years. More than a fifth were older than 65, a category more at risk from severe COVID. Five cases of COVID were seen in participants receiving the booster compared with 109 who got the placebo. The trial took place during a period when the Delta variant was prevalent. The average time between second and third doses was about 11 months, with a follow-up time of two-and-a-half months. The booster was effective regardless of age, sex, race, ethnicity, or underlying conditions.

Booster effective against Delta variant

It remains to be seen for how long a booster can protect. It is also hoped that newer vaccines giving much longer protection over time will soon become available.


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