Precision Immunization (2 of 3) (IMAGE) NASA/Johnson Space Center Caption Former astronaut Mark Kelly takes his flu shot during his lab testing in support of the NASA Twins Study with his brother Scott Kelly. Credit NASA Usage Restrictions Credit NASA License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.