Measles is a highly contagious virus that can remain infectious in a room for up to two hours after an infected person leaves. The incubation period from exposure to the hallmark rash is anywhere from seven to 21 days. The case definition of measles is marked by the ‘three Cs’: cough, conjunctivitis, and coryza (runny nose). Complications from measles affect populations including children under age five, pregnant women, adults over age 20, and immunocompromised persons. They can range from diarrhoea and ear infections to pneumonia, encephalitis, and death. On February 18, an individual unvaccinated for measles attended an event at Asbury University in Jessamine County, Kentucky. The Kentucky Cabinet for Health and Family Services confirmed that the individual was positive for measles on February 24. The event, billed as a spiritual revival, hosted approximately 20,000 people on February 17 and 18. It is yet to be determined how many of these attendees were exposed or susceptible to the virus.
This event is reminiscent of the one that began the measles outbreak in Rockland County, New York, in October 2018. An unvaccinated teen returned from Israel, which at the time was experiencing over 3,000 cases of measles. A New York State Association of County Heath (NYSACHO) publication reported that the teen attended five services in four days at a synagogue with a capacity of 10,000. This ultimately led to 313 confirmed cases of measles, 51.6% of which affected children aged one to nine years.
The Kentucky Division of Epidemiology and Health Planning reports that in Jessamine County, only 27.51% of six-year-olds have the recommended two doses of the measles–mumps–rubella (MMR) vaccine. The highest rate of MMR vaccination in the state is 41.21%. This is in stark contrast to the 2023 vaccination rates forecast by GlobalData epidemiologists for the entire US: 91.48% for two-dose MMR in children aged 19–35 months. The US Centers for Disease Control and Prevention (CDC) notes that the affected area of the 2018–19 NY outbreak had 77% vaccine coverage. According to the World Health Organization (WHO), 95% vaccine coverage is required to attain herd immunity against measles.
There are three types of exemptions that allow persons to decline vaccines for themselves or their children in the US: medical, religious, and personal belief. Medical exemptions apply when the individual has a condition that does not allow them to receive vaccinations, such as chemotherapy or immunocompromised status. A religious exemption applies when an individual’s sincere religious beliefs directly contrast with the receipt of the vaccine. To date, 44 states allow a religious exemption to vaccines for school attendance. Personal belief exemption is not well-defined, and only 15 states currently recognise it.
The reasons for vaccine hesitancy in Kentucky have not been concretely defined. In a 2020 study by Omar and colleagues, a health clinic in rural Kentucky found that 70% of vaccine-hesitant parents trusted their healthcare provider, but 80% expressed a desire for autonomy over their children’s vaccines, and 45% considered infection preferable to vaccination. The driving forces behind low vaccine compliance in Kentucky are now being investigated in a collaborative five-year project between the Kentucky Department for Public Health and the University of Kentucky College of Public Health entitled ‘Kentuckians Vaccinating Appalachian Communities’ (K-VAC).
The MMR vaccine is 93% effective with a single dose. A second dose raises effectiveness to 97%, and immunity is lifelong. CDC recommended scheduling of MMR doses is 12–15 months and four to six years of age. An MMRV (measles-mumps-rubella-varicella) vaccine is now also available and offers protection against chicken pox. Increased vaccine coverage in Kentucky and other states with low coverage will likely be sufficient to quell this potential outbreak and cease transmission in the future.