Researcher says improving your immune system could limit reaction to COVID-19 vaccine Understanding Covid-19 vaccine side effects By A.J. Nwoko | December 29, 2020 at 7:56 PM EST - Updated December 29 at 8:25 PM MIDLOTHIAN, Va. (WWBT) - Researchers with the Virginia Research Center in Midlothian, which has been a trial site for the Phase-3 Pfizer Vaccine trials say that since the vaccines were approved for emergency use authorization by the FDA, more than 2 million Americans have already received the vaccine with no serious reactions. Dr. Aaron Hartman, who has overseen much of the vaccinations at the trial site, says when side effects do occur, they are typically minor and develop after receiving the second dose of either vaccine once the immune system begins to produce antibodies.