WHO | Measles – Mexico

Mexico is experiencing a measles outbreak. Between 1 January and 2 April 2020, 1,364 probable¹cases of measles were reported, of which 124 were laboratory confirmed, 991 were discarded and 328 remain under investigation. The age of the confirmed measles cases ranged from three months to 68 years (median=20 years), and 59% were male. Analysis conducted by the National Reference Laboratory (InDRE) identified the genotype D8 (similar to other countries in the Region), linage MVs/GirSomnath.IND/42.16/ for 17 of the confirmed cases.

Of the 124 confirmed cases, 105 were in Mexico City, 18 in Mexico State, and one in Campeche State; the following is a summary of the epidemiological situation in each:

In Mexico City, 427 probable cases were reported, of which 105 were laboratory confirmed and 83 remain under investigation. Confirmed cases have been reported in 14 town halls including Gustavo A. Madero (53 cases), Miguel Hidalgo (14 cases), Iztapalapa (9 cases), Cuajimalpa de Morelos (8 cases), Alvaro Obregon (7 cases), Xochimilco (4 cases), Cuauhtémoc (2 cases), Tlahuac (2 cases), Tlalpan (2 cases), Coyoacán (1 case), Azcapotzalco (1 case), Milpa Alta (1 case), and Venustiano Carranza (1 case). All 105 confirmed cases in Mexico City were Mexican citizens, and 60% were male. The highest proportion of confirmed cases were aged between 20 to 29 years (28%), followed by 2 to 9-year-old (17%), 30 to 39-year-old (14%), one-year-old (11%), infants aged less than 12 months (11%), 10 to 19-year-old (10%), and 40 years or above (9%). Of the confirmed cases, only 15 (14%) had a proven² history of vaccination. Under vaccination may be linked with missed opportunities for vaccination, a lack of access to vaccination services, scheduling limitations impacting parent’s abilities to take their children to get vaccinated, or lack of vaccine stocks. The most recent confirmed case had rash onset on 2 April 2020 and was reported in the Gustavo A. Madero town hall.

In Mexico State, 162 probable cases were reported, of which 18 were laboratory confirmed and 65 remain under investigation. Confirmed cases were reported in eight municipalities of Mexico State including Tlalnepantla (5 cases), Ecatepec de Morelos (4 cases), Nezahualcóyotl (2 cases), Tecámac (2 cases), Toluca (2 cases), Atizapán de Zaragoza (1 case), Chimalhuacán (1 case), Naucalpan (1 case). These 18 confirmed cases were all Mexican citizens, and 56% were male. The highest proportion of confirmed cases was reported among 20 to 29-year-old (22%), followed by 1-year-old (17%), 2 to 9-year-old (17%), 30 to 39-year-old (17%), infants aged less than 12 months (11%), 10 to 19-year-old (11%) and 40-year-old or above (5%). Of the confirmed cases, three cases (33%) had proven history of vaccination. The most recent confirmed case in the State of Mexico had rash onset on 27 March and lives in the Tlalnepantla de Baz municipality.

In Campeche State, eight probable cases were reported, of which one was confirmed and seven remains under investigation. The confirmed case is a 5-year-old female resident of Champoton Municipality who had rash onset on 21 March 2020. The case has a proven history of vaccination. The probable place of exposure was Mérida City, Yucatán State.

The rash onset dates of the confirmed cases in Mexico were between 12 February and 2 April 2020. The Figure 1 shows the progression of the outbreak. An exponential increase of confirmed cases could be observed in the coming weeks.

Figure 1. Reported measles cases by rash onset date in Mexico. Between 12 February to 2 April 2020.

Source: Data published by the Secretary of Health of Mexico and reproduced by PAHO/WHO.

The WHO Region of the Americas was declared free of measles in September 2016. However, Venezuela and Brazil lost their ‘measles-free’ status on 1 July 2018 and 19 February 2019 respectively due to major measles outbreaks between 2018 and 2019. Of 35 Member States, 33 have maintained the ‘measles-free’ status. In 2019, 14 countries in the Region of the Americas reported confirmed cases of measles including Brazil (19,326 cases, including 15 deaths), the United States of America (1,282 cases), Bolivarian Republic of Venezuela (548 cases, including 3 deaths), Colombia (242 cases, including 1 death), Canada (113 cases), Argentina (107 cases), Mexico (20 cases), Chile (11 cases), Costa Rica (10 cases), Uruguay (9 cases), Bahamas (3 cases), Peru (2 cases), Cuba (1 case), and St. Lucia (1 case). Between 1 January and 4 April 2020, seven countries have reported confirmed measles cases including Brazil (2,194 cases, 4 deaths), Mexico (124 cases), Argentina (54 cases, 1 death), the United States of America (12 cases), Uruguay (2 cases), Chile (2 cases), and Canada (1 case).

Public health response

Actions implemented by the Health authorities include:

• Intensified epidemiological surveillance through active and retrospective institutional case finding, contact tracing, and monitoring of contacts;
• Vaccination activities in the field;
• Risk communication through the epidemiological notice;
• Training activities for field staff;
• Strengthening of the laboratory network.

WHO risk assessment

Measles is a highly contagious viral disease which affects susceptible individuals of all ages and remains one of the leading causes of death among young children globally, despite the availability of safe and effective measles-containing vaccines. The mode of transmission is airborne or via droplets from the nose, mouth, or throat of infected persons. Initial symptoms, which usually appear 10–12 days after infection, include high fever, usually accompanied by one of several of the following: runny nose, bloodshot eyes, cough, and tiny white spots on the inside of the mouth. Several days later, a rash develops, usually starting on the face and upper neck and gradually spreads downwards. A patient is infectious four days before the start of the rash 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.

Among malnourished children and people with greater susceptibility, measles can also cause serious complications, including blindness, encephalitis, severe diarrhea, 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.

Because of ongoing transmission, vaccination strategies and other actions are being implemented to control the outbreak by local and state level authorities in Mexico. There is a high risk of spreading of the virus due to high population density such as Mexico City, in which the high vaccination coverage could allow slow but steady transmission. At the regional level, the potential impact is considered moderate given the performance of routine immunization programs and prevention and control capacities in other countries in the region and the restrictions for travel in many countries and territories of the Region due to the pandemic of COVID-19.

Due to the current 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 brief periods, can result in increased numbers of susceptible individuals and raise the likelihood of outbreak-prone vaccine-preventable diseases (VPDs) such as measles.

WHO advice

Since 1 September 2017, the Pan American Health Organization WHO Regional Office of the Americas (PAHO/WHO) has been sharing information on these outbreaks with its Member States and has alerted of the risk of outbreaks occurring from imported measles cases, as well as of the possibility of re-introduction of the disease in areas with low vaccination coverage. In light of continuous reports of imported measles cases from other Regions and ongoing outbreaks in the Americas, PAHO / WHO urges all Member States to follow the new recommendations on the Guidance for Immunization in the context of the COVID-19 settings.

Among the recommendations for countries with measles outbreaks, the following are highlighted:

Vaccination

• Involve the National Immunizations Technical Advisory Group (NITAG) in decision-making on the continuity of vaccination services.
• In health care facilities where vaccination activities are carried out, it is essential that health care workers look for signs and symptoms of respiratory diseases and offer a surgical mask to patients with flu-like symptoms and refer them for medical evaluation, in accordance with local protocols for initial triage of suspected COVID-19 patients.
• Although there are currently no known medical contraindications to vaccination of a person who has had contact with a case of COVID-19, it is recommended to defer vaccination until quarantine has been completed (14 days after the last exposure).
• Under circumstances of vaccine-preventable disease (VPD) outbreak, the decision to conduct outbreak response mass vaccination campaigns will require a risk-benefit assessment on a case by case basis and must factor in the health system’s capacity to effectively conduct a safe and high-quality mass campaign in the context of the COVID-19 pandemic. The assessment should evaluate the risks of a delayed response against the risks associated with an immediate response, both in terms of morbidity and mortality for the VPD and the potential impact of further transmission of the SARS-CoV-2 virus.
• If an outbreak of a VDP occurs, the risk-benefit of carrying out an outbreak response vaccination campaign should be assessed taking into account the health system’s capacity to effectively conduct a safe and high-quality mass campaign in the context of the COVID-19 pandemic. The assessment should evaluate the risks of a delayed response against the risks associated with an immediate response, both in terms of morbidity and mortality for the VPD and the potential impact of further transmission of the SARS-CoV-2 virus. Should an outbreak response vaccination campaign be pursued, stringent measures are required to uphold standard and COVID-19 infection prevention and control, adequately handle injection waste, protect health workers and safeguard the public. Should an outbreak response vaccination campaign be delayed, a periodic assessment based on local VPD morbidity and mortality, will be required to evaluate risk of further delay.
• Immunization services should be resumed when the risk of transmission of SARS-CoV-2 has been reduced and the capacity of the health system has recovered sufficiently to resume these activities. It is likely that some level of SARS-CoV-2 transmission will still be in progress when services resume. Strict infection prevention and control measures and social distancing practices are likely to continue in the early stages of resuming the vaccination service. NITAG should advise the country on how to resume service and which populations should be prioritized.
• Vaccinate at-risk populations residing in areas where the measles virus is circulating that do not have proof of vaccination or immunity against measles and rubella, such as health personnel, people working in essential services companies, institutions with a captive population and transportation (hospitals, airports, jails, hostels, border crossings, urban mass transportation and others), as well as international travelers.
• Vaccinate at-risk populations (without proof of vaccination or immunity against measles and rubella), such as healthcare workers, persons working in tourism and transportation (hotels, airports, border crossings, mass urban transportation, and others), and international travelers.
• Maintain a vaccine stock of the measles-rubella (MR) and/or MMR vaccine and syringes/supplies for prevention and control actions of imported cases.

Epidemiological surveillance

• Surveillance systems must continue to carry out early detection and the management of VPD cases, at a minimum for diseases with global surveillance mandates and elimination objectives such as measles and rubella, among others.
• During an outbreak and when it is not possible to confirm the suspected cases by laboratory, classifications of a confirmed case may be based on clinical criteria (fever, rash, cough, coryza and conjunctivitis) and epidemiological link, in order to not delay the response actions.
• Routine surveillance for other VPD should continue as long as possible; when laboratory testing is not possible, samples should be stored appropriately for confirmation when laboratory capacity permits testing. Countries should ensure sufficient sample storage capacity at the provincial and central levels and this should be monitored regularly.
• Strengthen epidemiological surveillance in border areas to rapidly detect and respond to highly suspected cases of measles.

Rapid response

• Provide a rapid response to imported measles cases to avoid the re-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 and local levels must be ensured, with permanent and fluid communication channels between all levels (national, sub-national, and local).
• During outbreaks, 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.

¹Mexico probable measles/rubella case definition: Any person of any age with fever and maculopapular rash, and one or more of the following signs and symptoms: cough, coryza, conjunctivitis, or adenomegaly (retroauricular, occipital, or cervical). Available here.

²Verified in the immunization record card.

For more information on measles: