Measles has returned to the United States with a vengeance even though it was officially eliminated in 2000. Since that date, until 2014, occasional outbreaks had occurred because of importation of the virus from remaining measles-prone areas of the world. In 2014, there were 667 cases. This year, by the end of April, the case count has reached 704; the last year in which more cases were recorded is 1994 when there were 963 cases. Given that it is the beginning of May, we will almost certainly exceed the 1994 case count this year (though we will likely not reach the 2237 case count of 1992). Given that experts expect one to two deaths per 1000 cases, we may see fatalities and these will very likely will be infants deemed too young for vaccination.
By now it is widely recognized that the resurgence of measles in the U.S. has been enabled by vaccine refusal as was shown by Olive et al. in their analysis of the antivaccine movement published last year. As noted earlier, measles cases occur in the U.S. because the virus is imported by travelers coming or returning from other countries with high measles activity. In 2019, out of 44 importations, the countries implicated so far have been Philippines (14 importations), Ukraine (8), Israel (5), Thailand (3), Vietnam (2), Germany (2), besides Algeria, France, India, Lithuania, Russia, and the United Kingdom contributing one each. Of the 44 importations, 40 were through unvaccinated individuals. Because international air travel volumes are expected to continue to increase, we may expect more such episodes in the future.
Lauren Gardner of Johns Hopkins University and I (along with two international collaborators, Kamran Khan in Toronto and Aleksa Zlojutro in Sydney) have modeled how vaccine refusal acts synergistically with air travel patterns to enhance measles risk. We have produced a spatial risk profile (sometimes called a “heat map”) at the county resolution for the continental U.S. (Our results are due to be published in The Lancet Infectious Diseases next Thursday and we are under an embargo not to reveal details and, so, I will only mention a few highlights in this post.) As expected, the centers of vaccine resistance identified by Olive et al. also emerge as high risk places in our analysis. But we show that the presence of busy international airports with a high volume of passengers from countries with measles activity also creates high risk in places with relatively low vaccine refusal rates.
In particular, if such places have local communities in which vaccine refusal is concentrated, they are likely candidates for large outbreaks. Brooklyn this year is an example. Neither Brooklyn County nor neighboring Queens County have high vaccine refusal rates. However, Queens hosts two busy international airports (JFK and La Guardia). Brooklyn is also home to several ultra-orthodox Jewish communities that have refused vaccines. There have been 423 cases of measles in Brooklyn and Queens, mostly in these Jewish communities, with the infection being introduced by an unvaccinated child who had traveled to Israel.
Three Texas counties are among the top twenty-five ones nationally at risk from measles outbreaks: Harris County is ranked highest, then Tarrant, and finally Travis. Harris County includes part of the Houston metropolitan area and is close to the George Bush International Airport and Tarrant includes part of Dallas-Forth Worth Airport. What drives risk in Travis County, which includes Austin, is the fourth highest vaccine exemption rate in Texas (after Blanco, Borden, and Jeff Davis counties, all of which have much lower populations). Harris has had four cases, Tarrant one; Galveston and Montgomery counties, with one case each, are adjacent to Harris. Denton with one case is contiguous to Tarrant; Collin with two cases just one county away. Though Travis County has yet to report a case, Bell and Guadalupe counties have each reported one case and are spatially just one county away from Travis.
We live with a very high risk of measles in Austin. Though our airport has only a handful of direct international flights, we do get a large number of international travelers. More importantly, not only does Travis County have a high vaccine refusal rate, like Brooklyn we have pockets of unvaccinated people in the city. This is partly due to the social network spawned by the presence of Andrew Wakefield, the defrocked British doctor who fraudulently claimed a connection between measles vaccination and autism. That study has been debunked and retracted by the journal that published it but still continues to impress some people.
In Austin, our problem communities are several schools. For measles, because of how highly contagious it is, we need a 95 per cent vaccination rate to achieve herd immunity, that is, a situation in which an incidental infection will not spread by cascading through the population. This means that no school or other community should cross a threshold of 5 per cent for vaccine refusal.
According to data provided by the Texas Department of State Health Services, none of our ISDs cross the 5 per cent vaccine refusal rate to become a problem. But as many as sixteen individual schools do. The worst is Austin Waldorf School with 49.01 per cent of its students having had refused vaccination in the 2017 -2018 academic year (which is the most recent time period for which data are publicly available). Then come Austin Discovery School with 32.18 %, Kirby Hall School with 27.38 %, Austin Montessori School with 21.96 %, Veritas Academy with 21.30 %, Headwaters School with 17.11 %, AESA Prep Academy with 14.58 %, Chapparal Star Academy with 13.12 %, Nyos Charter School with 10.12 %, Hill Country Christian School with 10.77 %, Griffin School with 9.48 %, Rawson Saunders School with 9.42 %, Montessori for all with 9.29 %, Wayside Schools with 8.44 %, Regents School with 8.18 %, and Brentwood Christian School with 7.85 %. We have no data on home schooled children many of whom are also likely to be unvaccinated.
How should we manage the resulting risk of measles outbreaks? The first and obvious response should be to vaccinate as effectively as possible. We must try to convince those who refuse vaccines to reconsider, at least for their children’s sake if not for themselves. (Though I am skeptical that these individuals will respond to rational persuasion, it behooves us to try.) Meanwhile it is most important to focus on those who are put at risk because of others’ vaccine refusal, most notably children. Measles vaccination is generally administered along with that for mumps and rubella (whooping cough) as part of the MMR vaccine or, for children between twelve months and twelve years, as part of the MMRV vaccine that also includes varicella (chicken pox). The CDC recommends two dose of the MMR vaccine, the first between twelve and fifteen months and the second between four and six years.
During an infant’s first twelve months, antibodies inherited from the mother may confer some immunity to infants but also make vaccination less effective. However, for international travel, the CDC also recommends a first dose of MMR at or after six months. Given the risk of an outbreak, this is a measure I suggest parents seriously consider and discuss with their pediatricians. New York City is already requiring early vaccination for infants in response to the crisis there. To the extent that it is legally possible, Austin should follow suit. Moreover, again according to the CDC, the second MMR dose can be given as early as 28 days after the first. I suggest that parents also consider this option though it is not as important as getting the first dose. (The first already confers a 93 per cent protection; the second takes it up to 97 per cent.)
The second response should be to minimize contact between unvaccinated individuals and those at risk of infection through no fault of their own. Once again, New York provides a precedent, though an extreme and controversial one, by banning unvaccinated children from public places and fining those who violate either this mandate or that for mandatory vaccination. These extreme measures are limited to areas with ongoing measles outbreaks and have only been imposed for a limited time. Should measles cases begin to appear in Austin in one of our communities with low vaccination rates, such drastic temporary measures should also be one the table. In such a circumstance, we should at least limit attendance in problem schools to vaccinated children and adults as well as limit access to libraries, parks, and public social events such as concerts.