Vaccines have been found to be the most successful and cost-effective public health measures that prevent illness and save lives. This is especially true between children around the world. During the latter half of the 20th century, diseases that used to be all too common became scarce in the developing world, mainly due to extensive immunization. Hundreds of millions of lives have been rescued and billions of dollars in public health expenditures have been rescued with extensive vaccinations.
thank you for your post @reddust, may be useful