I am very late to this thread. My wife and I, ages 70 and 67, respectively, lucked out and got our second Pfizer shots at a local hospital back in February. The website we found to register on had just opened and it got booked up shortly thereafter. Neither of us had any side effects with either shot. Side effects, when they occur, are usually associated with a very robust immune response, which basically means the vaccine is doing its job well. This occurs mostly in younger adults, or in people who had previously been exposed to COVID-19. My daughter, age 29, has had both Pfizer shots as well, because she works in an immunology lab with immune cells from COVID patients. She coauthored a journal article on that subject that is in peer review now. After her second shot, she spiked a 102 fever and felt like crap for about 24 hours. She advised me that if I felt some side effects after my second shot, to hold off on taking anti-inflammatories, including acetaminophen (tylenol), at least for a while, as it might somewhat suppress my immune response.