If an increase in vaccination rates leads to lower disease transmission in the community, what is the underlying cause of this positive externality?

When more people in a community get vaccinated, it helps protect not only themselves but also those around them. This is because vaccines reduce the chances of spreading diseases, which is a benefit that affects everyone, not just the vaccinated individuals. For example, if a child gets vaccinated against measles, they are much less likely to catch the disease and spread it to others, including those who cannot be vaccinated for health reasons. This situation creates a positive externality, as the community enjoys better health and lower disease rates without directly paying for those benefits. Therefore, the underlying cause of this positive externality is the collective immunity gained when vaccination rates increase, leading to safer environments for all.