THE TRAGEDY now unfolding in the Pacific island state of Samoa is a case study of how wrongheaded information about vaccines can lead to injury and death. Samoa’s population of about 195,000 is less than Arlington County’s, but it has suffered a major outbreak of measles that has led to 68 deaths, most of them children. It could and should have been prevented, and must be taken as a lesson for the rest of the world.

The Samoa outbreak can be traced back to July 2018, when two year-old children were given what was supposed to be the MMR vaccine that protects against measles, mumps and rubella. Both infants died. Later it was determined that two nurses had improperly prepared the inoculations by mixing in a lethal dose of muscle relaxant; one of the nurses tried to cover up the error. That nurse was charged with manslaughter and obstruction of justice and sentenced to 5½ years in prison in August; the second nurse was charged with manslaughter and received a five-year prison sentence.

The deaths shook confidence in the health-care system. The World Health Organization estimated that in 2018, only 31 percent of infants in Samoa received the measles vaccine, a drop from 60 to 70 percent in previous years. Measles is a highly contagious virus that is spread when an infected person coughs or sneezes, and it can remain in the air for up to two hours afterward. The disease can lead to serious complications and death, especially among children. The effective way to stop transmission is to immunize 93 percent to 95 percent of the population.

The low immunization rate in Samoa left unvaccinated children extremely vulnerable once measles began spreading in recent weeks. The government is now carrying out an emergency vaccination program.

Misguided information spread by those who advocate against vaccines appears to have made inroads in Samoa before the outbreak. The Post reports that anti-vaccine activist Robert F. Kennedy Jr.’s advocacy group, Children’s Health Defense, made several Facebook posts in July and August 2018 that questioned the safety of the vaccines the infants received. The charity did not update the posts to explain the nurses’ error to its audience. A recent study showed that 54 percent of the advertisements spreading false information about vaccines on Facebook were bought by two groups, one of them Mr. Kennedy’s. Mr. Kennedy on Nov. 19 wrote to the Samoan prime minister again raising a question about the safety of the vaccines, and has visited Samoa.

In fact, sound scientific studies have shown the vaccine to be safe and effective, and a 1998 study claiming a link between vaccines and autism has been discredited.

What is dangerous, as the Samoa crisis demonstrates, is to spread false information that leaves a community seriously vulnerable. The World Health Organization reports another major surge in measles around the globe over the past year. Bad information that leads people to hesitate about vaccines is a killer.

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