Nine vaccinated soldiers caught measles, and all of them had it mildly

On 6 August 2017, the Israeli Defence Force was notified of two suspected
measles cases. The investigation found nine, in a population with **high
measles vaccination coverage.** The primary patient **had recently travelled to
Europe**, where 15 countries had measles outbreaks that summer, and **every
other case was among his direct contacts.**

What the vaccine did

All nine had modified measles — **less severe disease, with a milder rash,
milder fever, or both**, with or without the other typical symptoms.

No tertiary cases occurred. The chain stopped at the second generation.

So the vaccine did not prevent these infections, and it changed both things
that matter: how ill each person became, and whether they passed it on.

And what that costs

The same mildness is the problem the report is written about:

**Modified measles might not be suspected in persons with documentation of
vaccination.**

A vaccinated patient with a mild rash and a low fever looks like a dozen
harmless things. The clinician has a vaccination record in front of them, which
is a reason not to think of measles — and measles is the most contagious
disease there is.

Hence the instruction, which runs against the instinct:

**In outbreak settings, health care providers should maintain a high index of
suspicion for measles, even in vaccinated patients, and conduct a thorough
epidemiologic and laboratory investigation of suspected cases.**

What it took to contain

Nine mild cases, nearly fourteen hundred contacts traced. That ratio is the
standing argument for high coverage: the vaccine turned what would have been a
serious outbreak into nine mild illnesses, and the investigation was still
enormous.

Source: Centers for Disease Control and Prevention, MMWR.