Population Displacement

The Syrian crisis has significantly impacted public health in Lebanon. Lebanon is currently hosting the highest concentration of refugees worldwide. ^{Reference Rossi, Assaad and Rebeschini13} The influx of more than 1 million Syrian refugees into Lebanon who are living in poor sanitary conditions has created a favorable medium for the circulation of several infectious diseases. ^{Reference Ozaras, Leblebicioglu and Sunbul2} Several infectious disease outbreaks have been noted in Lebanon in correlation to the huge influx of Syrian refugees into the country. ^{Reference Ozaras, Leblebicioglu and Sunbul2} The overcrowded Syrian population in these areas might have promoted measles transmission. ^{Reference Hammoud, Onchonga and Amer11} The majority of displaced Syrian refugees lived under crowded conditions with poor infrastructure, without access to proper hygiene and sanitation. ^{Reference Helou, Van Berlaer and Yammine1} The influx of Syrians has overwhelmed the Lebanese health system. The need of primary health-care services increased by 50%, mostly for women and children, overwhelming Lebanese public hospitals. Hence, the situation hindered the refugees’ access to health-care services. ^{Reference Helou, Van Berlaer and Yammine1}

Immunization

The immunization schedule for measles was revised in March 2014, whereby children were to receive a zero dose (MCV0) at 9 mo, followed by a first dose of MMR (including the first dose of the measles vaccine [MCV1]) at 12 mo and a second dose of MMR (including the second dose of the measles vaccine [MCV2]) at 18 mo. ^{Reference El Zarif, Kassir and Bizri7} The estimated global coverage of MCV1 has seen a significant rise from 72% in 2000 to 85% in 2010, ^{Reference Patel, Gacic-Dobo and Strebel14} but Lebanon is still among countries with <90% coverage with MCV1. ¹⁵ The data show that, of individuals in Lebanon who contracted measles between 2003 and 2018, an average of 9.66% were vaccinated against the virus, 38% had an unknown vaccination status, and a mean of 52.26% were confirmed as nonvaccinated. ^{Reference El Zarif, Kassir and Bizri7} In 2019, Kmeid et al. evaluated the vaccination status of 571 Syrian and Lebanese children. They demonstrated low compliance with the measles vaccine (55-70%) and a higher compliance with the MMR vaccine (96-100%). The lack of vaccination among children is a major cause of the outbreak. ^{Reference Farah, Saleh and Abou El Naja3} Socioeconomic factors play a major role in vaccination compliance, and contracting measles is itself associated with a significant economic burden. A recent study found several factors that hinder vaccination, including socio-demographics, knowledge, beliefs, and practices associated with age-appropriate vaccination. ^{Reference Mansour, Said and Brandt16} Different factors contribute to the low vaccination coverage in adults. Lack of knowledge and hesitancy are common causes. A study conducted recently about perception of vaccination in Lebanese adults showed that 25.6% are not aware of the need of vaccines and 27.9% thought it is not indicated. ^{Reference Sakr, Helou and Hamieh17} Adults have concerns and fear about vaccination products. Around 40% agree or are uncertain whether vaccines contain harmful chemicals and around 50% believe that vaccines can trigger diseases. ^{Reference Sakr, Helou and Hamieh17} The possibility that nonvaccinated individuals may be clustered together should be considered, suggesting that the estimated vaccination coverage rates do not reflect the status of the general population but rather represent that of a higher-risk subpopulation.

Prevention

Vaccination campaigns are a quick and effective method of catching up with the vaccination status of children when this appears to be suboptimal. ^{Reference Rossi, Assaad and Rebeschini13} However, campaigns are logistically and financially challenging and cannot replace routine vaccination services, which require reinforcement. ^{Reference Rossi, Assaad and Rebeschini13}

In addition, regardless of vaccination status, active surveillance of measles contacts should be implemented. In fact, secondary measles contraction in vaccinated individuals can present with atypical symptoms, leading to viral circulation in the absence of active monitoring.

The surveillance system in tracking vaccination status must be improved through encouraging families to retain home-based records. This is to be bolstered by routine revaccination of high-risk individuals, including health-care workers and contacts of measles cases. Based on our data, the outbreaks in Lebanon were detected and the numbers were adequately reported, despite having the highest number of refugees per capita. A World Health Organization (WHO) assessment mission was conducted in 2016 to assess the national surveillance system in Lebanon, results showed compliance of 93%. ^{Reference Farah, Saleh and Abou El Naja3} It is essential to keep active surveillance even in these difficult times to control this outbreak. Awareness should be created and invested in to target different audiences and inform them of the importance of vaccination.

Measles outbreak has spread by means of a population movement across the borders. Awareness and prevention should be conducted within Lebanon and the neighboring countries to prevent spread. International collaboration and assistance in implementing effective prevention strategies (like vaccinating refugees crossing from country with an outbreak) is needed.

The resurgence of measles is multifactorial. Several factors can be responsible for the transmission and resurgence of measles: population density, inter/intra-age contact, timing of vaccination, and waxing conferred immunity.