We investigated pro- and anti-vaccine rhetoric on two South African Facebook pages to identify the nature, sources and justifications of the vaccine-related claims published on these pages. Our dataset consisted of 440 Facebook posts made by page administrators during 2019. Statements related to the safety and necessity of vaccines dominated the pro-vaccine page, while the anti-vaccine page focussed primarily on claims about the dangers of vaccines. Posts on both pages frequently contained content shared from within Facebook, with much of the content originating from the United States. Both pages made equal use of scientific justifications (i.e. published journal articles) to support claims, and most of these articles were published in accredited journals. The authors hope that a better understanding of the nature, sources and justifications of pro- and anti-vaccine rhetoric may lead to more constructive dialogue about vaccines, including the ongoing debate about COVID-19 vaccines.