Book excerpt: Penguin Readers is an ELT graded reader series for learners of English as a foreign language. With carefully adapted text, new illustrations and language learning exercises, the print edition also includes instructions to access supporting material online. Titles include popular classics, exciting contemporary fiction, and thought-provoking non-fiction, introducing language learners to bestselling authors and compelling content. The eight levels of Penguin Readers follow the Common European Framework of Reference for language learning (CEFR). Exercises at the back of each Reader help language learners to practise grammar, vocabulary, and key exam skills. Before, during and after-reading questions test readers' story comprehension and develop vocabulary. Visit the Penguin Readers website Exclusively with the print edition, readers can unlock online resources including a digital book, audio edition, lesson plans and answer keys. This book is about viruses and was written during the Covid-19 pandemic. Learn about bacteria and viruses - from the common cold to smallpox, polio, Ebola and the Zika virus. Then meet some of the scientists who discovered ways to prevent these diseases, and those who are working with viruses today.