Enemy At the Gate by Philippa Werry

"Being in quarantine sounds like being in prison," I said, shivering. Lily nodded. "A bit like that. Except that the prison is your own home."
"Or like being in a besieged castle," I said, thinking aloud. "With an invisible enemy at the gates."

In 1936 a deadly disease holds New Zealand in terror. Known as infantile paralysis, or polio, the disease appears to strike at random. Schools close. Going to the pictures is out of the question. Seeing your friends is dangerous.

Caught up in the confusion and fear, twelve-year-old Tom finds refuge in his dream: to run in the Olympics like the famous Jack Lovelock.