Vaccines are among the most ingenious of inventions, and among the most maddening.

Some global killers, like smallpox and polio, have been totally or nearly eradicated by products made with methods dating back to Louis Pasteur. Others, like malaria and H.I.V., utterly frustrate scientists to this day, despite astonishing new weapons like gene-editing.

We have a vaccine for Ebola that protects nearly 100 percent of its recipients, but we are lucky to get a routine flu shot that works half that well.

We have children’s vaccines against measles, mumps, rubella, diphtheria, whooping cough, tetanus, chickenpox, polio, hepatitis A and B, rotavirus, pneumococcus, haemophilus influenzae and meningococcal disease.

They have changed our expectations of mortality — and of parenthood. In 17th century England, one-third of all children died before age 15. Today, thanks largely to those vaccines, less than 1 percent of English children do.