Figures from 1997-2004 were administrative statistics which reflects the utilisation of immunisation service offered by Maternal and Child Health Centres (MCHC) under the Department of Health as at September 2019. As some children receive vaccination from their private doctors and some babies born to Mainland women would return to Mainland China shortly after birth and receive vaccinations there, these coverage may not reflect the actual coverage of Hong Kong children. In order to better reflect the immunisation coverage, official estimates are provided from 2005 onwards, mainly based on the results of the immunisation coverage survey on preschool children conducted by Department of Health in 2001, 2003, 2006, 2009, 2012, 2015 & 2018.

A new vaccination timing for Hepatitis B vaccination (viz 6 months after birth) has been adopted by the Department of Health since 1.9.2000, in place of the previous one (viz 3-5 months after birth). Figures from 1997-2000 refer to the percentage of children aged 3-5 months while figures from 2001-2004 refer to children aged 6 months having received the 3rd dose of HBV vaccine. Figures from 2005 onwards refer to the immunisation coverage of 3rd dose of HBV vaccine in preschool children.