While long-term side effects are theoretically possible with any treatment, this vaccine is based on a platform that's been safety-tested repeatedly in experiment vaccines for prostate cancer, MERS, malaria, tuberculosis, influenza and chikungunya virus, so there's a lot of past safety data. In addition because the main effect of the vaccine is to trigger a strong immune response, you would typically see side effects in the short term related to that initial response (things like Guillain-Barré syndrome or Transverse myelitis), not over the long term as the effect wanes.