This study has been supported by the following grants, National Research Foundation Singapore Investigatorship (NRF-NRFI2016-01) awarded to S-M. L. and NRF Competitive funding (NRF2017NRF-CRP001-027) awarded to S-M.L and P.J.B. S-M.L., P.J.B. and C.S.V. thanks Ministry of Education, Singapore (MOE2012-T3-008) for support. This work was also partially supported by NIH grants AI142759, AI127744, and AI136126, and awards from the Kleberg Foundation, John S. Dunn Foundation, Amon G. Carter Foundation, Gilson Longenbaugh Foundation, and Summerfield Robert Foundation to P.Y.S. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.