On January 25, Washington’s governor declared a public health emergency in response to a growing measles outbreak that has impacted Clark and King counties. There have been 39 confirmed cases as of January 30, with the majority of cases (38) being reported in Clark County. Twenty-seven of the cases are younger than age 10, 10 are age 11-18 years, 1 is age 19-29 years, and 1 is over the age of 50. Nearly all of the cases in Clark County were unvaccinated (34 total), while the remaining four have an unverified immunization status. Multnomah County, Oregon, which sits just across the Columbia River from Clark County, and Hawai’i have also reported cases connected to the Washington outbreak (OR-1 case, HI-2 cases), although it is not clear if these are already included in the case count reported above. The 2 cases in Hawai’i were exposed in Washington and detected in Hawai’i when they developed symptoms; they have since returned home to Washington.

Increasing measles incidence, particularly among unvaccinated individuals, is an extremely concerning trend across the US. In 2018, there were 349 cases of measles in the US, the second highest yearly total since the US eliminated measles in 2000. Large outbreaks resulted from unvaccinated travelers acquiring the disease overseas and importing it to their home communities, which were also often unvaccinated. For example, an unvaccinated child that contracted measles during a trip to Israel was the index case for an ongoing measles outbreak in an Orthodox Jewish community in Brooklyn that has resulted in 62 confirmed cases since October 2018. Vaccine hesitancy (ie, the “reluctance or refusal to vaccinate”) was recently listed by the WHO as one of the top ten threats to global health in 2019, citing the 30% global increase in measles incidence as just one of many growing threats to the “progress made in tackling vaccine-preventable diseases.” Outbreak Observatory has previously written about the resurgence of measles in both the United States and the United Kingdom.

Washington and Oregon are two of 18 US states that currently allow for philosophical, non-medical vaccination exemptions for parents who do not want their children to be vaccinated. For the 2017-2018 school year, kindergarten vaccination coverage rates were below the US median of 94.3% in both states (93.2% in OR and 90.6% in WA). Some counties in these states were much lower, including Clark County, where just 77.4% of public school students are up-to-date on their vaccinations. Furthermore, two counties in Washington (King and Spokane) and one in Oregon (Multnomah) are ranked among the 15 metropolitan areas with the most kindergarten non-medical exemptions—King and Multnomah counties are in the top 5—creating “hot spots” that are vulnerable to outbreaks of vaccine-preventable diseases such as measles.

Public health practitioners in Washington and Oregon must now begin the difficult and resource-intensive task of contact tracing (ie, identifying and notifying potential contacts of the known cases). These individuals could have been exposed to measles in a variety of public places, including healthcare facilities, schools and daycare centers, churches, museums, restaurants, pharmacies, and shopping centers. Exposures may have also occurred at the Portland International Airport, which could make contact tracing particularly challenging. Clark County has also established a call center for those concerned about possible exposures.

Importantly, lawmakers in Washington recently introduced a bill that would ban personal exemptions for the MMR vaccine, although it does not eliminate these exemptions for other vaccines such as DTaP/Tdap for diphtheria and pertussis. This effort will likely not benefit the current outbreak, but it is certainly an important step in the right direction to mitigate the risk of future measles outbreaks.

Photo: US Public Health Service announcement, signed by the Surgeon General, to raise awareness of the importance of measles vaccination (circa 1960s); courtesy of US CDC.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.