Answer:
Unless you are a trained health care professional, this is difficult at best and impossible at times. The best approach is to look at information from multiple sources from reliable health care entities and not just from an individual's or group's opinions or blogs. There is an extremely large bank of incorrect information on the Internet about vaccines. Much of this is not based on actual study and is often related to sales of products instead of facts or is generated out of fear instead of knowledge. It can also be based on a few incidents that may seem to be important to an individual, but likely are only based upon an untrained perception or based on too few accounts of the incident and leaps of logic. Rely only on proper resources for all health information. See the related link for more information on how to discern among all the sources which is likely sound information.
If you have concerns, ask your doctor if the information is credible. Do not try to interpret information for yourself unless you have medical training.
Never spread information to others that you read that you have not researched for yourself. You may be doing everyone a disservice, creating unnecessary fears, or promoting someone's product that bases their claims on inaccurate or deliberately misleading information to enhance sales.
See the related link below for some valuable information about determining validity of information about vaccines on the Internet. That information is also good to apply to all types of information and not just healthcare information.