To research and explore the antibody protection and immune memory after vaccination in children with KHE during sirolimus administration. To explore the feasibility (safety and efficacy) of vaccination in a timely manner during the administration of sirolimus in children with KHE. To search for back-up plans for vaccination regimens for KHE patients taking sirolimus in children who do not respond to primary vaccination.

Children with KHE have an early onset. KHE usually occurs in infants and young children less than 1 year old, of which neonates account for about 38.5%-60% of all cases. Due to the immunosuppressive effect of sirolimus, the vaccination was usually suspended after taking it, and children would be in a state of no immune protection. These children are at greatly increased risk of exposure to microorganisms and consequent infection. Therefore, it is necessary to vaccinate them against infectious diseases. However, vaccination with live vaccines has the potential to cause severe infections through reversion of the vaccine strain to a pathogenic form. Moreover, studies have also shown that protective antibodies are severely affected in transplant patients taking immunosuppressive drugs and in patients with solid tumors after chemotherapy. Loss of immune memory is very common, and marked deficits in B cell function and humoral immunity can persist even for years.

Inclusion Criteria:

• Case groups:
• KHE patients treated with sirolimus.
• After immunoglobulin and flow cytometry assays, as well as outpatient evaluation and assessment, those participants will be vaccinated with live attenuated vaccines or inactivated vaccines in a timely order according to the advice.
• Control groups:
• Healthy children with no immune deficiencies.
• Participants are vaccinated according to the National Immunization Program in a timely manner.
• Participants are matched to the case group according to age.

Exclusion Criteria:

• HBsAg, HBeAg positive, or other active infectious diseases;
• History of immunodeficiency or low immunoglobulin levels;
• Autoimmune disease or fever during blood collection;
• Use of other medication or surgery;
• Suffering from other bleeding disorders;
• Suffering from other solid tumors or hematological tumors, etc.;
• Withdraw informed consent.

The calculation of the sample size came from the previous pre-experiment. Investigator take HBsAb protection rate as the main outcome indicator. The sample size of this study, calculated using a non-inferiority test, was 156 (78 per group). In addition, 10% was required to make up for loss to follow-up, withdrawal, etc. So a total of 174 subjects (87 per group) are anticipated.