Chi C LEUNG

Deputy Editor, Respirology,
Honorary Consultant, Hong Kong Tuberculosis, Chest and Heart Diseases Association

[Chi C LEUNG @CclLEUNG]

What's really going on with flu this winter? - BBC News https://t.co/UJaf09awrc

[Chi C LEUNG @CclLEUNG]

@COVID19_disease The rather modest Covid-19 wave due to XDV lineage is coming down in both Mainland China and Hong Kong SAR. With now an endemic infection, it is EXTREMELY unlikely that a single mutation will turn it to another pandemic: such mutation should be selected long ago!!!

[Chi C LEUNG @CclLEUNG]

Antigenic drift with changing dominant strains is expected for SARS-COV-2, just like influenza or other ENDEMIC respiratory viruses showing repeated reinfections.
NB.1.8.1 (an XDV sublineage) caused only a minor wave compatible with time-relared waning herd immunity in Hong Kong.

[Chi C LEUNG @CclLEUNG]

Low natural circulation after last summer likely accounts for current Covid wave in Hong Kong. Covid naive infants at risk after maternal antibodies drop. XDV NOT new: in China since last year. Viral strains diversify across the globe: antigenic drift driven by herd immunity.

[Chi C LEUNG @CclLEUNG]

@mrmickme2 @T_Brautigan @guptalab @jbloom_lab @yunlong_cao @VirusesImmunity @JeremyFarrar @SGriffin_Lab @sigallab @Tuliodna @mvankerkhove While attack on conserved epitopes provides a ready mechanism for a broad spectrum antibody, it may NOT be easy to find such mechanism for a mutant capable of evading polyclonal antibodies. Immune suppression is NOT likely to occur before infection.

[Chi C LEUNG @CclLEUNG]

@EricTopol @yunlong_cao Covid-19 is now endemic. Everyone in the population could have a chance of exposure during daily social gathering. Passive immunity through nasal spray of antibody may be limited by short lasting protection. Any chance of a nasal vaccine capable of broad spectrum coverage???

[Chi C LEUNG @CclLEUNG]

@EricTopol As the incidence of DM has not exploded after Covid, SHARED RISK FACTORS for clinically diagnosed covid (because of increased incidence &/or severity) & type 2 DM could be a more important factor for the observed association between Covid & DM.

[Chi C LEUNG @CclLEUNG]

@EricTopol With a high R0, SARS-COV-2 has rapidly adapted to new human host. High background transmission has dampened cyclic/seasonal oscillations. Increasing fitness costs of further mutations also limit the impact of their immune invasion. Pandemic well over but vulnerable still at risk.

[Chi C LEUNG @CclLEUNG]

@outbreakupdates Uncontrolled spread of H5N1 in farm animals raised in LARGE herds allows sustained large scale viral replication to breed and sustain stepwise mutations.

Current H5N1 control appears to fail among diary cows. Stop the transmission among cows is necessary to avert pandemic.

[Chi C LEUNG @CclLEUNG]

@DaniBeckman The movement of people may complicate the transmission picture, especially with long flight. As the current technology to control airborne spread is by DILUTION, it is NOT efficient for highly transmissible Covid-19! SOURCE CONTROL before aerosol spread is MUCH MORE EFFECTIVE!

[Chi C LEUNG @CclLEUNG]

@CDCFlu The source of the threat is missing in the diagram. Without circulation of H5N1 in the farm herd, the risk will not have existed. As farm workers can be exposed in SO MANY WAYS, there is NO way to eliminate the zoonotic outbreak risk without clearing the virus from the farm.

[Chi C LEUNG @CclLEUNG]

@outbreakupdates "ADAPTING" may not be the right word at this stage in the absence of evidence of ongoing transmission WITHIN any human population.

While the CHANGING virus is still at zoonotic stage, there seems little success or even intention to control its circulation in farm animals.

[Chi C LEUNG @CclLEUNG]

@EricTopol An O.R. of just 1.8 is perhaps TOO LOW to support causality between antigen persistence and long Covid. Ongoing SARS-CoV2 reexposure/reinfection +/- symptoms likely accounts for part of antigen and/or symptom persistence.

[Chi C LEUNG @CclLEUNG]

@Bob90407225 @COVID19_disease Omicron lineage, estimated R0 of ~10 >> many respiratory viruses: full adaptation, further structural change by mutation of RNA genome likely involves fitness cost.
Herd immunity builds up with FREQUENT reinfection (+/- s/-): selection for immune evasion despite fitness cost.

[Chi C LEUNG @CclLEUNG]

@Mike_Honey_ The rate of spread in both time and space of XEC might still appear too slow to rule out other current or future competitors.

The diversity and appearance of recombinants suggest MINOR differences in transmission advantage of all these variants in endemic stage.

[Chi C LEUNG @CclLEUNG]

@UseBy2022 Major Antigenic Shifts: key to viral adaptation in new host in pandemic stage, e.g. the early omicron BA1&BA2 waves.

With adaptation to new host in endemic stage, increasing fitness cost of major antigenic shifts, only minor antigenic drift: waning immunity is key to rebound.

[Chi C LEUNG @CclLEUNG]

@DrEricDing @ASPRgov Not only Covid-19 remains!
Key Public Health Questions also remain:
Who to test?
When to test?
WHAT TO DO if +ve?
WHO PAYS?

[Chi C LEUNG @CclLEUNG]

Vaccination Paradox:
Vaccination alone NEVER rapid enough to stop any brewing pandemic. CONTAINMENT at outbreak sites, esp in Africa, is the key for Mpox clade 1b at this stage. Prepare for but NOT rely on MASSIVE vaccination: LITTLE financial incentives before actual pandemic.

[Chi C LEUNG @CclLEUNG]

@DrEricDing Intensified case finding among those with s/s or risk factors is the first & key step in monkey pox containment. Detecting cases without identifiable sources allow initiation of isolation & quarantine. Only secondary spread reflects delay / failure of control.

[Chi C LEUNG @CclLEUNG]

As predicted, the minor Covid-19 rebound peaked at week 31 in Hong Kong well before the FliRT variants became predominant: WANING IMMUNITY causes the rebound in seasonal fluctuation. Antigenic drift is RESULT of selection pressure from herd immunity vs old dominant strains.

[Chi C LEUNG @CclLEUNG]

Cyclical fluctuation of Covid-19 in Hong Kong: The recent Covid-19 rebound is minor c.f. past waves. It is peaking as the total number and sewage level have begun to drop.