Effect Measure

However, during January 1--April 25, 2008, a total of 64 confirmed measles cases were preliminarily reported to CDC, the most reported by this date for any year since 2001. Of the 64 cases, 54 were associated with importation of measles from other countries into the United States, and 63 of the 64 patients were unvaccinated or had unknown or undocumented vaccination status. (CDC, Morbidity and Mortality Weekly Report)

Even with a highly contagious disease like measles, if you can vaccinate a high enough percentage of the population you can essentially wipe the disease out because a single infectious case cannot, on average, find enough susceptibles to spread. This is called herd immunity. It's not just that most people aren't susceptible. With good population coverage the virus doesn't circulate and you don't have measles without measles virus. The US has a quite well covered population so ordinarily wouldn't be subject to outbreaks. But the rest of the world hasn't caught up. There are an estimated 20 million measles cases globally. The virus still circulates freely outside the US and can come here on infected people.

We're not talking about illegal immigrants. We're talking about unvaccinated US citizens who travel abroad and unvaccinated foreign travelers who come to the US to visit from highly developed countries in Europe. Why weren't they vaccinated? Opposition to vaccination:

Thus far in 2008, five U.S. residents and five visitors have been documented as acquiring measles abroad. Of these 10 persons, nine acquired measles in the WHO European Region. These importations likely are related to an increase in 2008 in measles activity in Europe. In Switzerland, approximately 2,250 measles cases have been reported since November 2006. The Swiss measles outbreak started in Lucerne, where the measles vaccination coverage level in children is 78%, and spread across the country, predominantly affecting children aged 5--15 years who were unvaccinated because of parental opposition to vaccination. In Israel (which is included in the WHO European Region), a measles outbreak with approximately 1,000 cases is ongoing (Ministry of Health, Israel, unpublished data, 2008), and measles transmission is occurring in other European countries, predominantly among populations opposed to vaccination.

The unvaccinated cases then infected unvaccinated US citizens. Some of those unvaccinated people, I am embarrassed to say, were health care workers. Moreover unvaccinated people tend to cluster geographically and socially. Failure to vaccinate is itself contagious. This makes outbreaks more likely since it creates pockets of susceptibles in which the disease can spread. And when this happens it endangers others. Like my little grandson who has almost, but not quite yet, reached the age of routine of first vaccine dose (12 - 15 months). Creeping resistance to measles vaccination has led to large scale measles outbreaks in the UK and The Netherlands. It would be a shame to see innocent children harmed here by the same kind of irrational and socially destructive refusal to do a responsible thing we see in some European countries.

At the moment we don't have endemic, smoldering and ongoing measles transmission in the US. Yet we know it can happen here because the virus is periodically imported. We can't get Europeans to act responsibly. But we can protect ourselves and our neighbors and our neighbor's children and our neighbor's grandchildren.