Vaccination prices have gone from single digits to sometimes triple digits in the last two decades, creating dilemmas for doctors and their patients as well as straining public health budgets. Some doctors have stopped offering immunizations because they say they cannot afford to buy these potentially lifesaving preventive treatments that insurers often reimburse poorly, sometimes even at a loss. Childhood immunizations are so vital to public health that the Affordable Care Act mandates their coverage at no out-of-pocket cost and they are generally required for school entry. Old vaccines have been reformulated with higher costs. New ones have entered the market at once-unthinkable prices. Together, since 1986, they have pushed up the average cost to fully vaccinate a child with private insurance to the age of 18 to $2,192 from $100, according to data from the Centers for Disease Control and Prevention. The costs for the federal government, which buys half of all vaccines for the nation's children, have increased 15-fold during that period. The most expensive shot for young children ... is Prevnar 13, which prevents diseases caused by pneumococcal bacteria, from ear infections to pneumonia. Each shot is priced at $136, and most states require children to get four doses before entering day care or preschool. Pfizer, the sole manufacturer, had revenues of nearly $4 billion from its Prevnar vaccine line last year.