He and his colleague, Dr. Stanislaw Matulewicz, knew the big bad Nazi soldiers lived in fear of epidemic typhus, which is when you catch regular typhus but thoughtfully brought enough to share with the whole class. The Nazis refused to arrest anybody with the virus, because God forbid somebody with a deadly disease infect everybody else at the death camp.
If they ran into a situation where too many people had it in one area, they Germans would just quarantine the whole place and leave everybody to get sick and die in peace. Lazowski and Matulewicz decided to exploit this, but knew it wouldn't be enough to simply scream "typhus!" any time an Indiana Jones antagonist wandered into the neighborhood. No, faking an epidemic would mean injecting everyone with freaking typhus.
"Surprisingly, this is covered by your HMO."
They actually crafted a vaccine made out of dead typhoid cells, as they had discovered that patients injected with the vaccine would test positive for epidemic typhus, though they wouldn't actually have the disease. So they did what any responsible doctor might -- they jabbed over 8,000 Jews with phony vaccines, sent the positive results back to the German occupiers, sat back, and watched the fun. Sure enough, the Nazis reacted to the "epidemic" by setting a quarantine line, wishing the city luck, and running away as fast as they could.
Weeks later, some Nazis braved the area again -- since nobody was dying, they were suspicious that the plague might actually be bullschnitzel. Luckily, Dr. Lazowski had a plan -- he wined and dined the senior officials until they found absolutely no reason to do boring shit like "investigate medical fraud." Instead, they sent the rookie guards to do so in their stead. Being young and dumb, these Nazis were extra-petrified of typhoid. They stuck around just long enough to collect a few blood samples (which naturally tested positive) and ran back to safety.
German Federal Archives
The Nazis eventually figured it out, but the doctors (and probably most of the quarantined) had already fled the country. Besides, they were far too busy losing the war to plan any sort of revenge. The "epidemic" had worked perfectly -- 8,000-plus people owe their lives to Lazowski and Matulewicz's chicanery.