"I started my pediatric residency program at Mount Sinai Hospital in New York City in 1983,"That was before the HiB vaccine came out, which protects against a bacteria called Haemophilus Influenzae Type B. "We used to see so many children with very serious bacterial infections due to this bacteria — pneumonia, meningitis, sepsis. And after the vaccines came out and had been given for a number of years, we really no longer see those infections."