Why are side effects more intense with the second COVID-19 vaccine dose? Amy Graff FacebookTwitterEmail This is normal and shouldn't deter people from completing their vaccines series, experts say. In trials of both the Moderna and Pfizer vaccines, more people experienced side effects after the second dose. "The early advice we gave people who were getting vaccinated was that when you’re getting your second shot, you can tell your employer, 'Hey I’m getting my second shot, it may be that I call in sick,' so then you anticipate it and you're not afraid of it," said Dr. Peter Chin-Hong, an infectious disease expert at UCSF.