There’s no study to confirm that covid vaccination is totally safe for breastfeeding women, so they suggested to suspend breastfeeding for 5-7 days; as your baby will be absorbing the vaccination from breastmilk. Refer to this poster for more information, it’s very easy to understand if you need other information. https://www.nuh.com.sg/PublishingImages/COVID-19%20Vaccine%20-%20What%20You%20Need%20To%20Know%20-%20Infographic%202021.pdf