Since November 29, the United Kingdom has been battling an outbreak of measles, totaling 70 confirmed cases across the country. Outbreaks have been confirmed in five areas across England: Leeds, Liverpool, Surrey, Manchester, and Birmingham, and Public Health England (PHE) states that the cases are all children and adults who have received less than the two recommended doses of the MMR vaccine. All of the cases are linked to even larger outbreaks occurring in other European countries, including Romania and Italy.
Last week, we reported on an outbreak of a mumps in the United States, another highly contagious, childhood vaccine-preventable disease. Despite being an ocean apart, the two outbreaks share many common public health characteristics. We identify and examine several of these similarities below.
Measles: a preventable childhood disease
Like mumps, measles is a highly contagious viral childhood disease. Symptoms include fever, cough, conjunctivitis, and a characteristic rash which usually appears about 14 days after exposure. Measles can be transmitted either by direct contact or through the air by sneezing, breathing, or coughing. It is one of the most contagious diseases known to man, with an average case capable of infecting between 12 and 18 other people. According to the CDC, one infected person can infect 90% of susceptible exposed individuals close to that person, even before the appearance of a rash. The virus infects the respiratory tract before spreading throughout the body, and death usually occurs due to neurological and respiratory complications (e.g., encephalitis, pneumonia).
Measles can be prevented by vaccines administered during childhood—typically, the same vaccines used to protect against mumps. The two vaccines typically used are the measles-mumps-rubella (MMR) vaccine and the measles-mumps-rubella-varicella (MMRV) vaccine. The US CDC and PHE both recommend two doses of the MMR vaccine during childhood: one dose is 93% effective against measles, while two doses increase the efficacy to 97%. The MMR vaccine is more effective at protecting against measles than mumps (for which it is 88% effective for those who are fully vaccinated), although this added protection may be partly offset by measles’ high transmissibility.
Individuals who have not received the MMR vaccine are at highest risk of becoming infected. According to the WHO, unvaccinated young children are at highest risk of catching measles and experiencing serious complications—including encephalitis, pneumonia, and severe diarrhea—that could result in death. The WHO states that measles “is one of the leading causes of death among young children.” In 2016, approximately 90,000 people died from measles globally, and most of these were children under the age of 5. Other at-risk groups include pregnant women, adults over the age of 30, and malnourished individuals. During a surge in cases in the US between 1989 and 1991, measles resulted in death in 2.2 out of every 1,000 cases, but the case fatality in developing countries can reach 25%.
Challenges to vaccine coverage
As previously mentioned, PHE has confirmed that all of the measles cases have been individuals with a deficient MMR vaccination status. These circumstances are similar to the mumps outbreak currently affecting the US state of Hawaii, where it is believed individuals who were improperly vaccinated or not vaccinated at all may be contributing to its spread (although this has not been confirmed).
As with victims of mumps in the US, reduced vaccine coverage may be playing a role in UK residents’ susceptibility to measles. Vaccine coverage data for the first quarter of 2017 reveals that while 95.8% of 5-year-olds in the UK have received one dose of the MMR vaccine, only 88.2% have received two doses. Coverage rates for the MMR booster are also slightly lower in England compared to Northern Ireland, Scotland, and Wales, which could be contributing to the ongoing outbreak. Because measles is so contagious, even small differences in vaccination coverage—or even small differences in second dose coverage—could have significant impacts on the spread of outbreaks. MMR vaccination rates in England dropped noticeably in the period between 1998 and 2004—to a low of 79.9% in 2003-04—following the publication of a highly controversial and long-since–discredited study published in 1998 claiming a link between MMR vaccination and autism.
Outside of the UK, Europe, as a whole, faces challenges to vaccine coverage. The European Centre for Disease Prevention and Control (ECDC) notes that the spread of measles across Europe “is due to suboptimal vaccination coverage.” It states that, of all measles cases reported in European countries between November 1, 2016 and October 31, 2017, 87% of cases were unvaccinated individuals.
Importing cases from abroad
As previously mentioned, the UK measles cases are epidemiologically linked to outbreaks occurring elsewhere in Europe. This includes primarily Romania and Italy, which have been the hardest hit countries in the Eurozone for 2017. According to ECDC data, Romania reported 7,977 measles cases and Italy reported 4,854 measles cases as of December 2017. PHE notes that any unvaccinated people in the UK returning from or travelling to Romania and Italy are at particularly high risk. While trends in measles incidence vary annually, Europe as a whole has witnessed a sharp increase in cases in 2017 compared to last year. According to the ECDC, there were 18,866 cases of measles in Europe between July 1, 2016 and June 30, 2017, as compared to 1,818 cases between July 1, 2015 and June 30, 2016. This represents a roughly 10-fold increase, which puts the UK population at greater risk as well.
Similarly, an outbreak of measles in Minnesota this summer—which affected 79 persons, the majority of which were of Somali descent — was most likely imported from Somalia or another country where measles is endemic, although the exact source is unknown. The Minnesota public health department spent $2.3 million to contain that outbreak, underscoring the serious economic burden of responding to outbreaks of vaccine-preventable diseases.
Globally, the target vaccine coverage needed to achieve measles elimination is 95%; however, a recent assessment of the WHO’s Global Vaccine Action Plan reports that between 2010 and 2016, global vaccine coverage for a second dose of measles-containing vaccine was only 64%. Until higher global vaccination rates are achieved — with the eventual goal of completely eradicating measles and other childhood vaccine-preventable diseases — outbreaks will continue to occur in pockets of unvaccinated persons, even in countries, such as the UK and the US, where these viruses are non-endemic, due to their importation through travel abroad.
Photo: A 3-D graphical representation of a spherical-shaped measles virus particle
Photo courtesy of CDC / Allison M. Maiuri, MPH, CHES
Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.