Dr TO, Kelvin Kai-Wang


BSc, MBBS, FRCPath, FHKCPath, FHKAM (Pathology), FRCP (Edin), MD


Department Chairperson and Clinical Associate Professor, Department of Microbiology

Email: kelvinto@hku.hk


ORCID : https://orcid.org/0000-0002-1921-5824



Research Interests

Respiratory tract infection is one of the leading causes of morbidity and mortality worldwide, affecting persons of all ages. Moreover, many of the pandemics in the past decades involves respiratory pathogens. Our research focus on impactful studies to improve clinical practice and guide real-time public health responses. Our strategies include:

1. Diagnostic advancement: development and evaluation of novel diagnostic tests, including the use of novel specimen types such as deep throat saliva;

2. Disease surveillance: viral genome analysis for early detection of emerging viruses or viral variants;

3. Disease dynamics indagation: elucidation of the pathogenesis, viral kinetics, host response and long-term immunity of COVID-19, including reinfections or breakthrough infections

4. Population surveillance: prevalence studies of COVID-19 and influenza virus, including the use of seroprevalence studies to unmask the hidden burden of infection in the community;

5. Vaccines: identification of novel topical vaccine adjuvants


Selected Publications

Omicron variant

1.  Chen LL, Abdullah SMU, Chan WM, Chan BP, Ip JD, Chu AW, Lu L, Zhang X, Zhao Y, Chuang VW, Au AK, Cheng VC, Sridhar S, Yuen KY, Hung IF, Chan KH, To KK. Contribution of low population immunity to the severe Omicron BA.2 outbreak in Hong Kong. Nat Commun. 2022 Jun 24;13(1):3618. doi: 10.1038/s41467-022-31395-0. 

2.  Chen L, Chu AW, Zhang RR, Hung IF, To KK. Serum neutralisation of the SARS-CoV-2 omicron sublineage BA.2. Lancet Microbe. 2022. https://doi.org/10.1016/S2666-5247(22)00060-X

3.   Cheng VC, Ip JD, Chu AW, Tam AR, Chan WM, Abdullah SMU, Chan BP, Wong SC, Kwan MY, Chua GT, Ip P, Chan JM, Lam BH, To WK, Chuang VW, Yuen KY, Hung IF, To KK. Rapid spread of SARS-CoV-2 Omicron subvariant BA.2 in a single-source community outbreak. Clin Infect Dis. 2022 Mar 10:ciac203. doi: 10.1093/cid/ciac203. Epub ahead of print. PMID: 35271728. 

4.    Chen LL, Chua GT, Lu L, Chan BP, Wong JS, Chow CC, Yu TC, Leung AS, Lam SY, Wong TW, Tsang HW, Wong IC, Chan KH, Yuen KY, Ip P, Kwan MY, To KK. Omicron variant susceptibility to neutralizing antibodies induced in children by natural SARS-CoV-2 infection or COVID-19 vaccine. Emerg Microbes Infect. 2022 Jan 27:1-17. doi: 10.1080/22221751.2022.2035195. Epub ahead of print. PMID: 35084295.


5.     Lu L, Mok BW, Chen LL, Chan JM, Tsang OT, Lam BH, Chuang VW, Chu AW, Chan WM, Ip JD, Chan BP, Zhang R, Yip CC, Cheng VC, Chan KH, Jin DY, Hung IF, Yuen KY, Chen H, To KK. Neutralization of SARS-CoV-2 Omicron variant by sera from BNT162b2 or Coronavac vaccine recipients. Clin Infect Dis. 2021 Dec 16:ciab1041. doi: 10.1093/cid/ciab1041.


6.     Zhao H, Lu L, Peng Z, Chen LL, Meng X, Zhang C, Ip JD, Chan WM, Chu AW, Chan KH, Jin DY, Chen H, Yuen KY, To KK. SARS-CoV-2 Omicron variant shows less efficient replication and fusion activity when compared with delta variant in TMPRSS2-expressed cells. Emerg Microbes Infect. 2021 Dec 24:1-18. doi: 10.1080/22221751.2021.2023329.


7.     Wong SC, Au AK, Chen H, Yuen LL, Li X, Lung DC, Chu AW, Ip JD, Chan WM, Tsoi HW, To KK, Yuen KY, Cheng VC. Transmission of Omicron (B.1.1.529) - SARS-CoV-2 Variant of Concern in a designated quarantine hotel for travelers: a challenge of elimination strategy of COVID-19. Lancet Reg Health West Pac. 2021 Dec 23:100360. doi: 10.1016/j.lanwpc.2021.100360. Epub ahead of print.



1.   To KK, Tsang OT, Leung WS, Tam AR, Wu TC, Lung DC, Yip CC, Cai JP, Chan JM, Chik TS, Lau DP, Choi CY, Chen LL, Chan WM, Chan KH, Ip JD, Ng AC, Poon RW, Luo CT, Cheng VC, Chan JF, Hung IF, Chen Z, Chen H, Yuen KY. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis. 2020 May;20(5):565-574. doi: 10.1016/S1473-3099(20)30196-1


2.   To KK, Cheng VC, Cai JP, Chan KH, Chen LL, Wong LH, Chi CY, Fong CH, Ng AC, Lu L, Luo CT, Situ J, Chung TW, Wong SC, Kwan GS, Sridhar S, Chan JF, Fan CY, Chuang VM, Kok KH, Hung IF, Yuen KY. Seroprevalence of SARS-CoV-2 in Hong Kong Special Administrative Region and our returnees evacuated from Hubei province of China: a multi-cohort study. Lancet Microbe. 2020; https://doi.org/10.1016/S2666-5247(20)30053-7


3.   To KK, Hung IF, Ip JD, Chu AW, Chan WM, Tam AR, Fong CH, Yuan S, Tsoi HW, Ng AC, Lee LL, Wan P, Tso E, To WK, Tsang D, Chan KH, Huang JD, Kok KH, Cheng VC, Yuen KY. COVID-19 re-infection by a phylogenetically distinct SARS-coronavirus-2 strain confirmed by whole genome sequencing. Clin Infect Dis. 2020 Aug 25:ciaa1275. doi: 10.1093/cid/ciaa1275.


4.   To KK (Corresponding author), Tsang OT, Yip CC, Chan KH, Wu TC, Chan JM, Leung WS, Chik TS, Choi CY, Kandamby DH, Lung DC, Tam AR, Poon RW, Fung AY, Hung IF, Cheng VC, Chan JF, Yuen KY. Consistent Detection of 2019 Novel Coronavirus in Saliva. Clin Infect Dis. 2020 Jul 28;71(15):841-843. doi: 10.1093/cid/ciaa149.


5.   Chan WM, Ip JD, Chu AW, Tse H, Tam AR, Li X, Kwan MY, Yau YS, Leung WS, Chik TS, To WK, Ng AC, Yip CC, Poon RW, Chan KH, Wong SC, Choi GK, Lung DC, Cheng VC, Hung IF, Yuen KY, To KK (Corresponding author). Phylogenomic analysis of COVID-19 summer and winter outbreaks in Hong Kong: An observational study. Lancet Reg Health West Pac. 2021 May;10:100130. doi: 10.1016/j.lanwpc.2021.100130.


6.   Ip JD, Kok KH, Chan WM, Chu AC, Wu WL, Yip CC, To WK, Tsang OT, Leung WS, Chik TS, Chan KH, Hung IF, Yuen KY, To KK (Corresponding author). Intrahost non-synonymous diversity at a neutralising antibody epitope of SARS-CoV-2 spike protein N-terminal domain. Clin Microbiol Infect. 2020 Oct 31:S1198-743X(20)30661-3. doi: 10.1016/j.cmi.2020.10.030.


7.   Chan JF, Yuan S, Kok KH, To KK (co-first author), Chu H, Yang J, Xing F, Liu J, Yip CC, Poon RW, Tsoi HW, Lo SK, Chan KH, Poon VK, Chan WM, Ip JD, Cai JP, Cheng VC, Chen H, Hui CK, Yuen KY. A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster. Lancet. 2020 Feb 15;395(10223):514-523. doi: 10.1016/S0140-6736(20)30154-9.




1.   To KK, Yip CC, Lai CY, Wong CK, Ho DT, Pang PK, Ng AC, Leung KH, Poon RW, Chan KH, Cheng VC, Hung IF, Yuen KY. Saliva as a diagnostic specimen for testing respiratory virus by a point-of-care molecular assay: a diagnostic validity study. Clin Microbiol Infect. 2019 Mar;25(3):372-378. doi: 10.1016/j.cmi.2018.06.009.


2.   To KK, Chan KH, Ho J, Pang PK, Ho DT, Chang AC, Seng CW, Yip CC, Cheng VC, Hung IF, Yuen KY. Respiratory virus infection among hospitalized adult patients with or without clinically apparent respiratory infection: a prospective cohort study. Clin Microbiol Infect. 2019 Dec;25(12):1539-1545. doi: 10.1016/j.cmi.2019.04.012.


3.   To, KK, Hung, IF, Li, IW, Lee, KL, Koo, CK, Yan, WW, Liu, R, Ho, KY, Chu, KH, Watt, CL, Luk, WK, Lai, KY, Chow, FL, Mok, T, Buckley, T, Chan, JF, Wong, SS, Zheng, B, Chen, H, Lau, CC, Tse, H, Cheng, VC, Chan, KH, & Yuen, KY. (2010). Delayed clearance of viral load and marked cytokine activation in severe cases of pandemic H1N1 2009 influenza virus infection. Clin Infect Dis 50, 850-859.