The doctor was giving a talk among colleagues. Only Gates himself can disprove the comment. Just because the Gates Foundation approves of vaccines for third world poor, does not equate to proof that he vaccinated his own children.
See the link that refutes the story as Fake News from a site that itself says that the stories on its website may not be accurate.
From the site that says Gates didn’t vaccinate his kids:
THE PEOPLE’S VOICE, INC. AND/OR ITS SUPPLIERS MAKE NO REPRESENTATIONS ABOUT THE SUITABILITY, RELIABILITY, AVAILABILITY, TIMELINESS, AND ACCURACY OF THE INFORMATION, SOFTWARE, PRODUCTS, SERVICES AND RELATED GRAPHICS CONTAINED ON THE SITE FOR ANY PURPOSE.