New Data On Johnson & Johnson Booster Shot

The COVID vaccine initially caused a significant increase in antibodies, but the booster shot showed even better results. Studies from the US and Europe revealed that people who received the booster 6 to 8 months after the initial shot experienced a ninefold increase in antibodies compared to those who received it 28 days later. Based on this data, the company is advancing with the booster shot development.

What regions were involved in the studies mentioned in the text?

How much higher were the antibodies after the booster shot compared to 28 days after the initial shot?