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Ben Cowling Profile picture
Ben Cowling
@bencowling88
Helen and Francis Zimmern Professor in Population Health, Chair of Epidemiology, School of Public Health, The University of Hong Kong
7 subscribers
Feb 22, 2023 • 16 tweets • 6 min read
New preprint on Omicron severity just out. Key findings – intrinsic severity of Omicron is similar to ancestral Wuhan strain, but effective (observed) severity of Omicron is reduced in people who have been vaccinated and/or previously infected (1/16)
medrxiv.org/content/10.110… In South Africa, Omicron caused a large number of infections in late 2021 but relatively low rates of severe disease, likely because of high population immunity from prior waves of infections. Omicron was mild, but would it always be mild elsewhere? (2/16)
thelancet.com/journals/langl…
Feb 2, 2023 • 14 tweets • 4 min read
New in @sciencemagazine #SciencePerspective “Managing sources of error during pandemics”. We discuss the emerging challenges we and others have faced in monitoring #COVID19 epidemiology now that the most acute phase of the pandemic is over (1/14)
science.org/doi/10.1126/sc… We discuss challenges in monitoring incidence of infections, the changing severity of infections, and the burden of infections including the number of hospitalisations and deaths. All of this information is valuable for risk assessment and consequent decision-making (2/14)
Dec 13, 2022 • 9 tweets • 3 min read
Brief thread on containment vs mitigation. Summary point - I hope there's a plan for intense mitigation measures in China in the next 1-2 months, as part of the transition to living-with-COVID
(1/9) In pandemic preparedness plans, this type of figure is often used to illustrate some key concepts. I have labelled the relevant periods. A is pre-pandemic preparation. B is containment, some countries will skip this if containment ...
(2/9)
(source: nyas.org/ebriefings/202…)
Oct 14, 2022 • 15 tweets • 4 min read
We have a new preprint (not yet peer-reviewed) on residential clustering of COVID-19 in Hong Kong, and the efficiency of residential Compulsory Testing Notices and Restriction Testing Declarations ("ambush lockdowns") led by @BenYoun11984381
medrxiv.org/content/10.110…
(1/15) (2/15) Residential clustering was a major feature of SARS in 2003 ... almost 20% of the 1755 SARS cases in Hong Kong resulted from one large super-spreading event in the Amoy Gardens housing estate in Kowloon
edition.cnn.com/2013/02/21/wor…
Oct 11, 2022 • 5 tweets • 2 min read
It's not at all surprising that the detection of cases in arriving travelers has increased, because (1) there's no more pre-departure PCR and (2) there's no more 3-day hotel quarantine but testing still goes out to day 6 ... (1/5) In the previous 3+4 system, with tests on 0/2/4/6, positivity with low Ct value on d4 was very unlikely (would have had to be a long incubation period or a within-hotel transmission), and d6 positives were mostly ppl who were infected on d3-4 with a short incubation period (2/5)
Oct 5, 2022 • 6 tweets • 2 min read
A few brief suggestions of how to proceed. Public health measures, such as masks and avoiding crowds and larger gatherings, could be recommended (but not mandated) for people to reduce their risk of respiratory virus infection (including COVID and influenza) ... (1/6) Healthcare settings and elderly homes should implement measures to minimise the frequency and impact of outbreaks of respiratory virus infections (including COVID and influenza), which could include staff masking and regular use of RATs by staff and patients/residents ... (2/6)
Aug 29, 2022 • 14 tweets • 4 min read
New preprint (not yet peer reviewed) on our randomized trial of third doses in HK, where BNT162b2 (BioNTech/Fosun Pharma/Pfizer) and CoronaVac (Sinovac) are the two available vaccines. With @nancyleung_hk @gmleunghku @svalko3 and others. Short thread(1/14)
medrxiv.org/content/10.110… Among adults ≥18y who initially received two doses of CoronaVac, we randomized 101 to a CoronaVac booster (“CC-C”) and 118 to a BNT162b2 booster (“CC-B”). Among adults ≥18 who initially received BNT162b2, we randomized 118 to “BB-C” and 114 to “BB-B” (2/14)
Aug 22, 2022 • 6 tweets • 2 min read
Hong Kong update - exponential rise in BA.4 and/or BA.5 (probably BA.5) continues. BA.2 cases now stable and will probably be declining soon, looks like we've hit herd immunity to this subvariant for now ... (1/6) Herd immunity to BA.2 under current public health measures has been reached by high incidence of BA.2 infections (providing strong long-lasting immunity against BA.2 re-infection) as well as transient protection against BA.2 infection from booster doses in some ppl ...(2/6)
Jul 15, 2022 • 4 tweets • 1 min read
I can see now where this 20,000 comes from ...
... the calculation is hinted at in this blog post ...
Jul 14, 2022 • 27 tweets • 6 min read
Increasing the stringency of home isolation for cases in Hong Kong, with electronic tracking bracelets, will have a minimal effect on transmission. Scientific basis for my assessment is in the thread which follows … (1/27) Article here in SCMP, “quarantine” in the title should actually be “isolation”. Quarantine is for people who test negative but who might already be infected and just not yet testing positive, the idea being to prevent any chance of transmission (2/27)
scmp.com/news/hong-kong…
Jul 13, 2022 • 4 tweets • 1 min read
From the SCMP article earlier today, I was surprised at the prediction of 10,000 patients needing hospitalization. The level of peak incidence would have to be very high to result in 10,000 patients needing hospitalization, now that we have high vaccine coverage and some ...(1/4) ... cross-immunity against BA.2.12.1, BA.4 and BA.5 from infections in the large fifth wave with BA.2 earlier this year.

Of course if every single case is hospitalized, we will run out of space, but - if hospital beds are reserved for those who need them - it's ... (2/4)
Jun 29, 2022 • 11 tweets • 3 min read
There's some discussion in HK about on-arrival quarantine periods. The purpose of on-arrival quarantine - a key part of a Zero Covid strategy - is to reduce the rate at which infections are "seeded" into the community from outside, perhaps with two objectives in mind: (1/11) 1. if local cases are zero each day, a new outbreak could require costly+disruptive control measures (think of Shanghai in April), and the fewer outbreaks the better. Less seeding means less outbreaks.

2. even if there is a local outbreak, preventing additional seeding... (2/11)
Jun 28, 2022 • 34 tweets • 10 min read
Thread on our new preprint (not yet peer reviewed) on the low but non-zero risk of COVID-19 transmission in quarantine hotels in Hong Kong, with @dcadam @gmleung @worldepidemic and other colleagues (1/32) medrxiv.org/content/10.110… Brief summary - we identify 6 additional cases of within-hotel transmission using epidemiologic data and virus sequence data. At least 12 such events occurred up to January 2022. We discuss how on-arrival quarantine can /delay/ but not ultimately /prevent/ local outbreaks (2/32)
May 16, 2022 • 24 tweets • 5 min read
My article with Theo Chan published today in Mingpao (in Chinese) argues that while COVID vaccines should be *recommended* for younger adults in HK, we believe there is insufficient justification at present to *mandate* vaccination in this group … (1/24)
news.mingpao.com/pns/%e8%a7%80%… … Stage three of the Vaccine Pass will start in HK on 31 May, by which time all applicable individuals aged ≥12 (except those with documented infection and in certain special groups) will need to have received at least two doses … (2/24)
May 3, 2022 • 10 tweets • 4 min read
New commentary with Mark Thompson just published, "How repeated influenza vaccination effects might apply to COVID-19 vaccines" ... thread follows ... (1/10)
thelancet.com/journals/lanre… (2/10) For many years, there has been interest in how immune responses to influenza vaccination seem to weaken with repeated annual vaccination, here is a key review article by @EdBelongia, Danuta Skowronski and others: tandfonline.com/doi/full/10.10…
Mar 30, 2022 • 6 tweets • 2 min read
Our new study published on vaccine hesitancy in Hong Kong from November 2020 through to July 2021 by Zoe Xiao and colleagues
thelancet.com/journals/lanwp… Two panels of Figure 2 below show levels of hesitancy, so higher numbers mean more hesitancy - initially a lot of hesitancy in younger individuals, like elsewhere in the world, but by July 2021 it was elderly that were most hesitant Image
Mar 23, 2022 • 15 tweets • 4 min read
I recommend children to get COVID-19 vaccination, but I don't think there's sufficient justification to *require* children to get vaccinated, and I'll explain my reasoning ... (1/15) ... if COVID vaccine coverage were low, and health officials were to explain why it needed to be high, while *other methods* to increase vaccination coverage had failed, I can see how there might be a rationale for considering ways to coerce vaccination ... (2/15)
Mar 22, 2022 • 18 tweets • 6 min read
We're able to report our estimates of the effectiveness of COVID-19 vaccines, led by @martinamc_m with @joshnealon @gmleunghku

Both BNT and Sinovac vaccines provide good protection against severe Omicron BA.2; but elderly who received 2xSinovac need a 3rd dose of vaccine
(1/15) (2/15) We used data on uptake of BNT162b2 and CoronaVac over time (overall uptake shown in figure here) to estimate population denominators with different levels of vaccination over time Image
Feb 24, 2022 • 6 tweets • 4 min read
Very glad to share that @NatureMedicine have published our article on the potential benefits of fractional dosing of COVID-19 vaccines by @du8491 and @fdlwang with @anup_malani @sarahcobey and other great colleagues and collaborators
(1/6)
nature.com/articles/s4159… We found that dose-sparing vaccination strategies could save a large number of lives, even with the emergence of new variants with higher transmissibility
(2/6)
Feb 19, 2022 • 10 tweets • 4 min read
(1/10) Recent situation in hospitals in HK is very concerning. Following tweet includes information complied from daily press releases each of which refer to the preceding 24h (I excluded info on the approx 2000 mild cases isolated in Penny's Bay) ...
...
14 Feb - 1600 COVID patients, 300 discharged + 2 died
15 Feb - 2482 patients, 233 + 10
16 Feb - 2654 patients, 238 + 10
17 Feb - 2866 patients, 214 + 24
18 Feb - 3099 patients, 251 + 10
19 Feb - 3312 patients, 246 + 15 discharged+died
...
(2/10)
Jan 11, 2022 • 4 tweets • 2 min read
This is interesting
One scenario - infected at Penny's Bay? (how?)
Another scenario - infected in community and detected now because she is in a frequently-tested group?
A third possibility - re-positive from an old infection or somehow a false positive? I coauthored this article 5 months ago about the need for an exit strategy from ZeroCovid once vaccine coverage is high enough
blogs.bmj.com/bmj/2021/08/11…

But if we are going to continue with ZeroCovid, I can provide advice on how to do it more successfully...