It is that time of year when you are likely to start seeing reminders to get your flu vaccine and encourage your loved ones to do the same. For identical twin astronauts Scott and Mark Kelly, their flu shots will happen almost in tandem, but while one is orbiting the Earth at 17,500 miles per hour, and the other is Earth-bound.

The vaccination is part of NASA's Twins Study, a compilation of multiple investigations that take advantage of a unique opportunity to study identical twin astronauts Scott and Mark Kelly, while Scott spends a year aboard the International Space Station and Mark remains on Earth.

Scott will receive his flu shot aboard the space station while his brother Mark will receive the same vaccine on Earth shortly thereafter. Blood will be drawn from both brothers before and after the vaccination, as well as throughout the duration of the one-year mission to compare how their systems respond to the vaccination.

A research study, called the Immunome Changes in Space investigation, led by Stanford University scientists Emmanuel Mignot, M.D, Ph.D., Mark M. Davis, Ph.D., and Michael Snyder, Ph.D., will look at how an astronaut's immune system changes in response to acute and prolonged exposure to microgravity and other spaceflight stressors and after return to Earth, whether these changes differ relative to Scott's earth-bound twin brother, and how they relate to physiological, molecular, genetic and biochemical changes.

Scientists already know that the body's immune system is altered during spaceflight due to factors such as stress, radiation, microgravity and altered nutrition. In space, some aspects of the immune system appear weakened, which could lead to infections. Other aspects appear overactive, which could cause allergy or hypersensitivity.

Understanding exactly which parts of the immune system are altered during spaceflight will help scientists know how to ensure that crew members maintain a healthy immune system during long flights, and stay protected against infections from Earth when visitors arrive at the space station. The data could also potentially be used to help develop new treatments and preventative measures for immune dysfunction and related health issues on Earth.

A better understanding of how the immune system is activated or suppressed may help in treating a range of auto-immune diseases such as arthritis and diabetes, and in treating the natural decline of the immune system as people age.

So while Scott and Mark Kelly might not be able to sit next to each other for support during the administration of their flu shots, they can take comfort in the knowledge that their tandem vaccinations are helping future crews and humans back on Earth stay healthy.