Disease Outbreak : Measles – Chile

Situation at a glance

On 12 August 2023, the IHR National Focal Point of Chile notified WHO of a confirmed case of measles in the Metropolitan Region. The case had history of travel to Georgia, where measles is endemic, and Armenia, where measles has been eliminated, and returning to Chile via Qatar and Brazil. To date no further cases related to this importation have been detected.

This is the first measles case reported in Chile since 2020. As soon as the case was notified, the local and national authorities implemented control measures, including case isolation and an epidemiological investigation to identify the exposed contacts and refer them for vaccination, and reinforced surveillance activities in the public and private health network.

Measles is a highly contagious acute viral disease but can be prevented by immunization. Chile interrupted local transmission of measles in 1993. Imported cases are expected, and the susceptibility of contacts determines the spread of the disease.

Description of the situation

On 12 August 2023, IHR National Focal Point of Chile notified WHO of a confirmed case of measles in the Metropolitan Region. The patient is a 42-year-old male from Chile with a history of travel to Armenia and Georgia (between 16 July and 26 July, returning to Chile on 26 July via Qatar and Brazil), and no history of vaccination against measles. This is the first imported case of measles reported in Chile since 2020.

On 7 August 2023, the patient presented with symptoms consistent with chills, myalgias, fever and malaise, twelve days after his return to Chile. On 8 August 2023, the case developed a rash (13 days after return) and on 9 and 10 August, he sought medical attention in two different health care facilities.

On 10 August 2023, serum and urine samples were collected and tested reactive for measles by IgM and PCR at a private clinic laboratory. On 11 August 2023, the samples were sent to the Public Health Institute of Chile, the national reference laboratory, where they tested reactive for measles by IgM and PCR on the same day. The patient did not require hospitalization, and as of 17 August, his progress has been favourable.

The patient has been in contact with about a thousand people through exposures at home, work, school, in waiting rooms of health facilities and others. As of 17 August, the contacts are under follow-up, and 325 contacts have received a dose of MMR, or standard immunoglobulin (for special groups), in the context of this outbreak, other contacts have accredited vaccination (National Immunization Registry- RNI per its acronym in Spanish or vaccination certificate) of two doses against measles, and the rest are still in the referral process to complete the missing doses.

In Chile, the current vaccination scheme considers the administration of two doses of measles, mumps and rubella (MMR) vaccine: the first dose at 12 months of life and the second dose at 36 months of age. Official measles immunization coverage in Chile with the first dose for MMR vaccine was 93.9% in 2022 and was 52.9% as of epidemiological week 26 of 2023, being below the percentage of sustained homogeneous coverage of at least 95% recommended by the WHO. According to WHO/UNICEF National Immunization Coverage (WEUNIC) estimates, Chile’s vaccination coverage with two doses of measles-containing vaccine (MCV2) was less than 60% over the past two years. In addition, within this national coverage, there are subnational variations (rural and peripheral urban areas) which could include pockets of unvaccinated people in all age groups.

Epidemiology of Measles

Measles is a highly contagious acute viral disease, which affects susceptible individuals of all ages and remains one of the leading causes of death among young children globally. The mode of transmission is airborne or via droplets from the nose, mouth, or throat of infected persons.

Early symptoms of measles are fever (as high as 40°C) and malaise, cough, coryza, and conjunctivitis, followed by a rash with both raised and flat areas (maculopapular rash). The rash usually appears 14 days after exposure and spreads from the head to the trunk to the lower extremities. A patient is infectious from four days before up to four days after the appearance of the rash. There is no specific antiviral treatment for measles and most people recover within 2-3 weeks.

Measles is usually a mild or moderately severe disease. However, measles can lead to complications such as pneumonia, inflammation of brain (encephalitis), and death. Postinfectious encephalitis can occur in about one in every 1000 reported cases of measles. About two or three deaths may occur for every 1000 reported cases of measles.

Among malnourished children and immunocompromised people including people with HIV, cancer and treated with immunosuppressives, as well as pregnant women, measles can also cause serious complications, including blindness, encephalitis, severe diarrhoea, ear infection, and pneumonia.

Measles can be prevented by immunization. In countries with low vaccination coverage, epidemics typically occur every two to three years and usually last between two and three months, although their duration varies according to population size, crowding, and the population’s immunity status.

The following public health measures were implemented by local and national health authorities:

• Intensification of epidemiological surveillance with active and retrospective institutional search for cases.
• Identification and follow-up of contacts for 21 days post-exposure.
• Vaccination of contacts if there was no immunization record.
• Use of standard immunoglobulin in the population at risk.
• Notification, through IHR NFPs, of contacts who travelled to other countries.
• Sending information to the IHR NFP of Georgia and Armenia for follow-up.

Additionally, during the second semester of this year, the updated strategy for students from 1st to 8th grade will be implemented in Chile ^[1].

Measles remains one of the leading causes of death among young children worldwide. It is highly contagious, with 90% of non-immune people exposed to an infectious individual estimated to contract the disease.

In 2016, the Region of the Americas was the first Region of WHO to be declared free of endemic transmission of measles viruses by the International Expert Committee (IEC) for Documenting and Verifying Measles, Rubella and the Congenital Rubella Syndrome in the Americas. Nevertheless, maintaining the Region free of measles is an ongoing challenge due to the permanent risk of importation and reintroduction of the virus. This case corresponds to a susceptible cohort of people born between 1971 and 1981 who were not immunized with two doses of MMR or did not previously present with the disease.

During the COVID-19 pandemic, there might be a risk of disruption to routine immunization activities due to both COVID-19 related burden on the health system and decreased demand for vaccination because of physical distancing requirements or community reluctance. Disruption of immunization services even for a short time can result in increased numbers of susceptible individuals and raise the likelihood of outbreak-prone vaccine-preventable diseases (VPDs) such as measles.

Measles anywhere is a problem everywhere because it spreads so easily. WHO recommends that countries in all regions continue to make progress towards achieving measles elimination in line with each of the endorsed Regional Goals of all WHO regions to achieve measles elimination, as well as the global strategy under IA2030, the Measles and Rubella Strategic Framework.

WHO recommends strengthening the efforts to implement the “Plan of Action for the Sustainability of Measles, Rubella, and Congenital Rubella Syndrome Elimination in the Americas 2018-2023“, with its four strategic sections: 1) guarantee universal access to vaccination services; 2) strengthen the capacity of epidemiological surveillance systems for measles, rubella, and congenital rubella syndrome; 3) develop the national operational capacity to maintain the elimination status; 4) establish standard mechanisms for rapid response to imported measles, rubella, and congenital rubella syndrome cases to prevent the re-establishment of endemic transmission in the countries.

WHO recommends strengthening epidemiological surveillance in high-traffic border areas to rapidly detect and respond to highly suspected measles cases. Providing a rapid response to imported measles cases to avoid the establishment of endemic transmission through the activation of rapid response teams trained for this purpose and by implementing national rapid response protocols when there are imported cases. Once a rapid response team has been activated, continued coordination between the national, sub-national and local levels must be ensured, with permanent communication channels between all levels. During outbreaks, it is recommended to establish adequate hospital case management to avoid nosocomial transmission, with appropriate referral of patients to isolation rooms (for any level of care) and avoiding contact with other patients in waiting rooms and/or other hospital rooms.

WHO recommends vaccination of at-risk populations without proof of vaccination or immunity against measles and rubella, such as health care workers, persons working in tourism and transportation (hotels, airports, border crossings, mass transportation, and others), and international travellers who are visiting measles endemic countries. Implementing a plan to immunize migrant populations in high-traffic border areas, prioritizing those considered at-risk, including both migrants and residents, in these municipalities increases vaccination coverage to increase population immunity.

In all settings consideration should be given to providing susceptible contacts with post-exposure prophylaxis (PEP), including a dose of MCV or normal human immunoglobulin (NHIG) (if available) for those at risk and in whom the vaccine is contraindicated. In well-resourced settings, MCV should be provided to susceptible contacts within 3 days. For contacts for whom vaccination is contraindicated or is not possible within 3 days post-exposure, consideration can be given to providing NHIG up to 6 days post-exposure. Infants, pregnant women, and the immunocompromised should be prioritized.

WHO recommends maintaining sustained homogeneous coverage of at least 95% with the first and second doses of the MCV vaccine in all municipalities and strengthening integrated epidemiological surveillance of measles and rubella to achieve timely detection of all suspected cases in public, private, and social security healthcare facilities.

WHO recommends maintaining a stock of the measles-rubella (MR)and/or measles, mumps, rubella (MMR) vaccine, and syringes/supplies for control actions of imported cases. Facilitating the access to vaccination services according to the national scheme to foreigners or people from the same country who perform temporary activities in countries with ongoing outbreaks; displaced populations; indigenous populations, or other vulnerable populations.

WHO does not recommend any restriction on travel and trade to Chile based on the information available on the current outbreak.

• Immunization Newsletter [Internet]. Washington (DC): Pan American Health Organization. Vol. XXXVIII, No. 3, September 2016
• Measles / Rubella Weekly Bulletin.
• Integrated Surveillance Information System for Vaccine-Preventable Diseases (ISIS). Plan of Action for the Sustainability of Measles, Rubella, and Congenital Rubella Syndrome Elimination in the Americas 2018-2023.
• IX Ad Hoc Meeting of PAHO’s Technical Advisory Group (TAG) on Vaccine-Preventable Diseases, 25 July 2022 (virtual).
• Measles. Washington, D.C: PAHO/WHO.
• PAHO/WHO Vaccine-Preventable Diseases.
• WHO – Measles vaccination coverage.

Citable reference: World Health Organization (23 August 2023). Disease Outbreak News; Measles – Chile. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON483

[1] https://vacunas.minsal.cl/wp-content/uploads/2023/07/2660-ORD-Informa-puesta-al-dia-vacuna-SRP-escolares-1%C2%B0-a-8%C2%B0-basico44.pdf