Pfizer results in more arm soreness after first shot than second, study says By Kali Coleman of Best Life | Pfizer results in more arm soreness after first shot than second, study says Side effects are common after many shots, but we've all been paying closer attention to them than ever with the COVID vaccine. For many, side effects have been more intense after the second dose than the first, whether it's the Moderna of Pfizer vaccine. However, a new study has found that one side effect is more common after the first Pfizer dose than the second. Read on to find out what reaction you should be anticipating after your first shot of the Pfizer vaccine, and for more on this specific vaccine, Pfizer's Vaccine Protects You for at Least This Long, Study Finds.