A canonical URL is a key tool in addressing the issue of duplicated content on your website. As you generate more content, such as news items or articles, it’s common for pages to have similar titles, content, and style, which can lead to duplication issues. Duplication of content can be a problem for Search Engine Optimisation. If a Search Engine finds two near-identical pages, it will not know which one should appear higher in the rankings.
To help solve this, when creating a new feature on your site such as a Flu news page, you can add a Canonical URL to the most up-to-date news item to help the Search Engine recognise that this is the most relevant and original version of this. Thus, enabling that content to appear higher in the Search Engine Results ranking.