evidence: Influenza vaccination – 7 things to know 21 October 2018 | Q&A Anyone can catch influenza, but certain groups have a higher risk of developing severe disease. WHO recommends vaccinating older individuals, young children, pregnant women and people with underlying health conditions. These are the groups most likely to suffer serious complications from influenza, which is why most countries prioritize them for vaccination. Health-care workers need to be vaccinated for their own protection and to reduce their risk of infecting vulnerable patients with the virus. [...] The influenza vaccine is the best tool we have for preventing influenza and reducing the risk of serious complications and even death. The effectiveness of the vaccine can vary from year to year, depending on the types of influenza viruses circulating and how well these match the vaccine. It also depends on the health status and age of the person vaccinated, as well as time since vaccination. On average, the vaccine prevents around 60% of infections in healthy adults aged 18–64 years. Influenza vaccines become effective about 14 days after vaccination.