In the UK as well as most other countries, flu vaccines are only licensed for use in babies aged over 6 months. The main concerns are not about harm, but about effectiveness. However, a study (Englund et al, 2016) in the United States of 1375 infants aged just 6-12 weeks confirmed that flu vaccine was safe and effective in this age group also, and therefore might be considered under special circumstances.
For babies under the age of 6 months, protection is reliant on the mother having a flu vaccine during pregnancy or whilst breastfeeding. This is one of the reasons why vaccinating a mother in pregnancy is strongly recommended, alongside other health benefits for the baby. Immunity is passed from mother to the newborn baby and offers protection until the baby can have it’s own flu jab from 6 months of age.