Each year millions of people from more than 180 countries gather to perform the annual Hajj pilgrimage in Makkah, Saudi Arabia. The Hajj season occurs at a fixed time each year from 8th to 13th day of the 12th month (Dhu al-Hijjah) in the Islamic calendar . The Islamic/Lunar calendar is 11 days shorter than the Gregorian calendar . This year the annual Hajj is expected to take place during August 8–13, 2019. The annual Hajj is one of the largest recurring mass gathering in the world and is the most studied mass gathering [1–8]. The number of pilgrims traveling to Saudi Arabia is based on the number of Muslims in each country and is calculated as one pilgrim per 1000 Muslims in the specific country . The annual pilgrimage number had increased from 58,584 in 1920 to 3,161,573 in 2012 and of those pilgrims in 2012 about 1,752,932 were international pilgrims coming from outside Saudi Arabia . The international pilgrims arrive to Saudi Arabia mainly by air and others may travel via land [4,8,9]. In previous years, there were occurrences of Hajj-related outbreaks [10–14] such as the 1987 international meningococcal disease outbreak caused by Neisseria meningitidis serogroup A [15–17], and serogroup W135 , and the 2000–2001 N. meningitidis outbreak [14,15]. Thus, the annual Hajj requirements are updated annually in response to the occurrence of newly emerging infectious diseases such as Middle East Respiratory Syndrome Coronavirus (MERS-CoV) [1,6,19] and the occurrence of international outbreaks such as Ebola [7,8]. The recommended vaccinations for the Hajj are updated annually [6–9,20]. The 2019 required and recommended vaccinations were issued by the Saudi Ministry of Health . Here, we summarize the 2019 Hajj mandatory and recommended vaccinations and discuss the possible impact of newly occurring outbreaks internationally, one of the most globally spread outbreaks is measles [21–23].