The use in war of chemical weapons was condemned by the general opinion of the civilized world and prohibited with the signing of the 1925 Geneva Protocol [
1]. Further prohibition includes the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (CWC), which became binding international law in 1997 [
2]. In violation of these prohibitions, some parties to war have used chemical weapons in conflicts [
3], including in Syria. Evidence of use of chemical weapons in Syria in the form of numerous toxic gas attacks has been reported by governmental and non-governmental international organizations since the Syrian war started in March 2011. Joint investigations by the Organization for the Prohibition of Chemical Weapons (OPCW) with the United Nations (UN) between April and November 2013 confirmed the use of chemical weapons in the Ghouta area of Damascus on 21 August 2013 and on a smaller scale, in Jobar on 24 August 2013, Saraqueb on 29 April 2013, Ashrafiah Sahnaya on 25 August 2013 and Khan Al Asal on 19 March 2013 [
4]. Later reports provided evidence with a high degree of certainty that chlorine gas was used as a weapon in the villages of Talmenes, Al Tamanah, and Kafr Zita from April to August 2014 [
5]. On 21 August 2015, the OPCW fact-finding mission (FFM) reported on the investigation of several incidents in the Idlib governorate between 16 March 2015 and 20 May 2015 and concluded that these gas attacks likely involved the use of sulphur mustard and in occasions combined with chlorine [
6]. The Syrian American Medical Society (SAMS) carried out parallel investigations involving the collection by medical staff of biological samples taken from the many patients treated after gas attacks and environmental samples collected from the area of attacks. SAMS identified the use of three toxic gases – Sarin, chlorine and mustard agents – and confirmed the findings of OPCW-UN investigations [
7]. In April 4, 2017 missiles launched from air allegedly loaded with toxic chemical gases attacked the town of Khan Sheikhoun in Idlib, Syria. The Violations Documentation Center (VDC) reported at least 92 identifiable deaths by the time of this study [
8] and others, even more [
9]. The medical humanitarian NGO, Médecins Sans Frontières (MSF) concluded that at least two toxic gases, Sarin and chlorine, may have been used in these attacks, based on evidence from MSF medical teams supporting the emergency department of Bab Al Hawa hospital and other hospitals [
10]. A joint FFM by the OPCW-UN reported the presence of Sarin or a Sarin-like substance in laboratory samples taken by the FFM team during the autopsies of three victims by this attack [
11]. To the date of this study, the Joint Investigative Mechanism (JIM) of the OPCW/UN, based on the FFM reports, concluded that the Syrian Air Force was the perpetrator of at least three attacks with chlorine (Kafr Zita - 18 April 2014, Qmenas - 16 March 2015 and Binnish, 24 March 2015). It also concluded that the Islamic State of Iraq and the Levant (ISIS/ISIL) perpetrated at least one attack with mustard agent (Mare’e, 21 August 2015) [
12]. Investigations and evidence of the use of chemical weapons in Syria reported by governmental and non-governmental international organizations are essential components of civilian protection.
The research community has so far contributed relatively little to civilian protection or to understanding the public health consequences of chemical weapons attacks in Syria [
13‐
16]. In earlier studies we described patterns of direct deaths and victim characteristics caused by the range of weapons used in the Syrian war from the beginning of the war in March of 2011 through December 2016 [
15,
16]. Here we use descriptive epidemiological analysis to address in detail the fundamental question of who have been the victims of the largest chemical weapons attacks in the Syrian war from March 18, 2011 to April 10, 2017.