Measles outbreaks: what does it represent for the elimination strategy in the region of the Americas? A call for the action

Abstract

The US is experiencing a large multi-state measles outbreak that started in California in 2014. At this time, no source case for the outbreak has been identified. Measles was declared eliminated in the US in 2000, because at that time, there were high coverage rates with the two-dose schedule and these vaccines have been very immunogenic. Measles is still endemic in many parts of the world, and outbreaks can occur when unvaccinated groups are exposed to imported measles virus. The current multi-state outbreak underscores the ongoing risk of measles importation, the need for high measles vaccination coverage rates, and the importance of a prompt and appropriate public health response to individual cases and outbreaks. The US outbreak threatens measles control in the Americas. Strengthening immunization programs and keeping vaccination coverage rates above 95% with a two-dose schedule will be necessary for measles control strategies in the Americas.

Keywords:

• children
• elimination
• measles
• outbreaks
• vaccine

Measles is one of the oldest vaccine-preventable diseases affecting children and adults. Most of the people who become ill will recover depending on a timely and adequate differential diagnosis, prompt treatment and prevention of disease spread. However, non-serious and life-threatening systemic, respiratory, gastrointestinal and neurological complications can occur and lead to death. Young infants, elderly people and pregnant women have a higher risk of becoming severely ill from measles [1,2].

Measles is highly contagious, outbreaks are common, and morbidity and mortality rates are considerable, particularly in developing countries. All these facts make measles a significant public health threat, not only for developing countries, but also for industrialized countries, and its associated economic and societal costs are considerable. The high transmissibility of measles allows immunity gaps to be revealed: low vaccination coverage rates, groups of accumulated susceptible individuals and vaccine refusal or marginalized groups [3,4].

Global measles control has been very successful. Estimated deaths fell by 74% from 535,300 in 2000 to 139,300 in 2010 [5]. Indeed, reduction in measles mortality accounted for 23% of the estimated decline in all-cause child mortality in children less than 5 years of age from 1990 to 2008 [5]. The WHO Global Vaccine Action Plan for 2012–2020 has established the target of measles and rubella elimination in at least five WHO regions by 2020, and Member States in all six regions have established goals to eliminate measles by 2020 or before. Elimination is defined as ‘the absence of endemic measles transmission in a defined geographical area, in this case all countries in a WHO region, for more than 12 months in the presence of a well-performing surveillance system’ [6].

The elimination of endemic measles transmission was achieved in the region of the Americas in 2002; since then, no endemic transmission of the disease has occurred for more than a decade despite ongoing incursions of virus from other parts of the world [4,5,7]. If we can declare our region free of this significant infectious disease threat, the Americas would be the first region in the world to eliminate the disease. This would be an achievement consistent with public health policies in the region that has positioned itself as a leading region in the control and elimination of several infectious diseases, such as polio due to wild poliovirus [7].

By May 2014, the US had experienced more cases of measles than in any other year since elimination was achieved, these could be due to imported-measles cases, producing subsequent outbreaks [3]. Brazil and Canada have also experienced large outbreaks in 2014 [3–5]. On the other hand, Mexico has already reported measles cases linked to the multi-state US outbreak that started in California’s Disneyland [8,9]. The US experienced 23 measles outbreaks in 2014 – 644 cases from 27 states, more than threefold higher than any previous year since 2000 – including one large outbreak of 383 cases, occurring primarily among unvaccinated Amish communities in Ohio. Many of the cases in the US in 2014 were associated with imported cases from the Philippines, which experienced a large measles outbreak. In 2015, the US reported four outbreaks and 173 cases from 1 January 1 to 6 March, mainly in unvaccinated individuals. The genotype identified in the amusement park’s outbreak was B3, the genotype responsible for the large outbreak in the Philippines in 2014. Genotype D8 has been identified in the outbreak of Brazil [10]. The genetic characterization of measles virus is an essential tool in the laboratory surveillance of the disease and route tracking of the outbreak, especially in countries that are approaching the measles elimination goal.

The presence of measles cases in four countries of the Americas complicates the goal of disease elimination, which is best evidenced by the fact that importation of cases is a current and continuous threat to the continent, and revealing that immunization rates in certain areas within countries have fallen below the levels needed to prevent the spread of disease in the Americas. Despite that, WHO reports that in the Americas, 92% of children have at least one dose of measles vaccine, with unprotected populations also being at higher risk for disease spread and outbreaks.

Undoubtedly, unvaccinated people are at risk, regardless of the reasons for not being vaccinated [11,12]. Despite the historic and strong evidence of safety and efficacy of vaccines against measles, there are still people who refuse the vaccine, considering it dangerous [13]. In 2011, the Institute of Medicine published a report that studied thoroughly the possible harmful effects of eight major vaccines, including the MMR vaccine [14]. In 2015, Klein et al. concluded that there was no evidence to suggest a causal relationship between MMR vaccine and autism, and that serious harmful effects from the vaccine were rare [15]. In 2014, the American Academy of Pediatrics published a review article of 67 studies finding strong evidence that MMR vaccine is not associated with autism [16]. This should convince public and healthcare workers that not vaccinating individuals with MMR is an error. Now, more than ever, the debate of vaccination as a human right and a duty of all citizens is necessary. This is the leading edge of vaccination practice and public health policies.

In summary, the goal of measles elimination in the Americas is jeopardized. Only through sustained and high vaccination coverage rates, awareness and education of public and healthcare workers, and effective surveillance, the risks of transmission and outbreaks can decrease. Pan American Health Organization and WHO recommend that children should receive two doses of measles vaccine before their fifth birthday and the coverage rates of both doses should reach >95% homogeneously in all geographic strata to prevent the spread of imported cases as much as possible. We strictly enforce these recommendations to sustain the regional goals and actively seek unvaccinated and vaccinated groups, complete vaccination schedules and implement follow-up campaigns, maintain high-quality surveillance and strengthen reference laboratories. To achieve and maintain measles elimination, these efforts should be implemented globally. Finally, the current measles epidemic most likely would have been prevented if the message, alerts, expert recommendations and predictions, which were given years before alerting about these threats, had been heard and visualized. It is now time to work again and recover our regression.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.