Supporting Information {#Sec1}
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The supporting information is available online at <http://life.scichina.com> and <https://link.springer.com>. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.

**Compliance and ethics**

The author(s) declare that they have no conflict of interest.

We thank Dr. Guodong Fang, a former infectious disease professor from the Peking Union Medical College Hospital and senior medical officer at the U.S. Food and Drug Administration, for helpful discussion. We thank Ms. Yu Li for her assistance in data collection. We also thank Dr. Bee Hong Lo, a visiting consultant pediatrician at the Children's Hospital at Westmead, for editing and proofreading this article.
