News media are inherently selective—both in what they report (selection bias) and how they present it (narrative bias). Selection bias refers to which events are covered or ignored, while narrative bias concerns how stories are framed through language, tone, and emphasis, shaping public perception. These production-side biases interact with confirmation bias on the consumer side: individuals tend to seek out news that aligns with their preexisting beliefs. This mutual reinforcement creates a feedback loop in which media outlets increasingly tailor content to ideological audiences—amplifying polarization, echo chambers, and misinformation. This seminar explores these dynamics through the case of the vaccine debate in Italy, offering a quantitative analysis of both selection and narrative biases. Results show that negative and extreme content attracts greater attention, and ideologically similar outlets tend to share their audiences—further reinforcing echo chamber effects. While narrative bias is effectively captured by third-party assessments, selection bias remains more elusive, highlighting the inadequacy of current evaluation criteria. Understanding and quantifying the different forms of bias is essential for promoting a more accurate and inclusive representation of global events in online discourse. Upholding journalistic integrity requires deliberate efforts to mitigate bias, ensure transparency, and embrace diversity in reporting practices and perspectives.