On today's episode of Ask The Doctor, experts say mixing of vaccine doses should be avoided unless there is no other option due to vaccine shortage. On the need for booster doses, doctors say currently the first priority is to get as many people vaccinated with at least one dose as possible, before we think about booster doses. Studies are underway to determine the need for a booster dose, based on how long immunity from vaccines last. On post-Covid lung infections and cardiac ailments, doctors recommend being cautious about frequently changing oxygen levels. Regular use of an oximeter or a spirometer to measure lung capacity post Covid recovery can help prevent cardiact arrests.