Hong Kong Citizen News have kindly agreed to publish my commentary on herd immunity. It's a long read, available here, grab a coffee: hkcnews.com/article/39405/… I published a similar commentary a few weeks ago in Chinese in Mingpao. I'll give a short summary in a new thread below
Herd immunity describes the situation where a high enough fraction of the population are immune that a large epidemic is no longer possible. Immunity can be acquired through infection or through vaccination (2/10)
In some parts of the world, herd immunity will be reached mainly through large numbers of infections. In other places like Hong Kong where infection rates have been kept low by successful public health measures, herd immunity could be achieved through vaccination (3/10)
Until Hong Kong can reach herd immunity, we won't be able to return to normal and stop all control measures. We could suppress "waves" and then temporarily lift measures when case numbers are low, but cases would rise again sooner or later (4/10)
We could aim for elimination like mainland China, Taiwan, Australia and New Zealand. But it's tough to get to zero cases, and it's tough to stay at zero cases, any outbreaks need to be quickly stamped out (5/10)
Higher vaccination coverage in HK would make elimination a bit easier, and an advantage of pursuing elimination would be the possibility of a quarantine-free travel bubble with mainland China or some other locations also aiming for elimination (6/10)
If we are able to achieve high vaccine coverage, we could drop all the control measures - no more closure of bars, cinemas, beaches, no more bans on social gatherings, no more contact tracing, no more on-arrival quarantines for persons arriving from anywhere in the world (7/10)
However, once we achieve herd immunity and reopen to the world, we would still expect COVID cases and outbreaks to occur from time to time, we wont expect COVID to disappear from the world time.com/5942246/elimin… (8/10)
That means that in this scenario, Hong Kong citizens likely might face the need to quarantine on arrival in mainland China or some other parts of the world that are still pursuing elimination, because those locations won't want to risk importation of infections (9/10)
For example, in mainland China, every small COVID outbreak in recent months has resulted in expensive lockdowns and mass testing exercises. Minimising introductions of infection is critical to maintaining successful elimination, and that requires on-arrival quarantines (10/10)
Should end the thread on a positive note - we have secured safe and effective vaccines and have the opportunity to get to herd immunity within 6 months. I’m looking forward to the chance to return to normal (11/10)
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As more and more people received #COVID19 vaccines in Hong Kong, it will soon be time to think about how immune status could modify our test-and-trace procedures locally (1/17)
tl;dr summary: I think vaccinated persons should still be isolated if testing positive, while quarantine duration could be reduced or even converted to medical surveillance for some fully vaccinated persons (2/17)
If you have respiratory symptoms, you should be tested for COVID, whether or not you have previously been infected, and whether or not you have been vaccinated. Testing is also done on contacts of known cases, as well as people living or working near known cases (3/17)
Key finding - between 23 January and 28 April 2020 in Hong Kong, we analysed contact tracing data and estimated that 19% of cases seeded 80% of all local transmission. For those interested in the dispersion parameter k it was 0.33 (95% CI: 0.14–0.98). nature.com/articles/s4159…
(2/18) We have seen daily case numbers decline in the past few days, and hopefully we have now passed the peak in our "third wave" (which is really a second wave here, because what is being referred to as the "first wave" in Hong Kong was not a wave ...). hk.appledaily.com/local/20200730…
(3/18) However, the local reproductive number has not dipped very far below 1. A reproductive number of exactly 1 would mean on average one case is infecting one further person, and daily numbers of cases would stay the same from week to week. The lower R is below 1, the better.
(1/9) Good news about COVID-19 suppression in Hong Kong, today we estimate that the daily reproductive number Rt dropped below 1 on 22 July, around a week ago covid19.sph.hku.hk
(2/9) There is a delay in estimates of Rt due to a 10-day lag between infections and laboratory confirmations, including an average of 5 days incubation period (time from infection to illness onset) and another 5 days on average between illness onset and laboratory confirmation.
(3/9) Since Rt fell below 1 on 22 July, we would expect the epidemic curve of cases by illness onset to reach a peak approximately 5 days after that (27 July), and the daily number of laboratory-confirmed cases to reach a peak within 7-14 days after 22 July.
(1/7) Worrying indications that the second wave of COVID-19 has now begun in Hong Kong, with more than 50 local infections being identified in the past few days and a large number expected to be reported later today.
(2/7) Our estimate of the effective reproductive number "Rt" for local infections is close to 3, which is concerning covid19.sph.hku.hk It will take a lot of effort to bring down such a high reproductive number.
(3/7) Clusters have been identified in an elderly home, a public housing estate, and linked with some restaurants. Test+trace has not prevented this. Mask-wearing in public is still universal, and has not prevented this. scmp.com/news/hong-kong…
Happy to read this op-ed in HKFP. People in Hong Kong have been wearing masks since early February, we always knew they would help even when public health authorities were advising against it hongkongfp.com/2020/06/29/i-w…
However I take exception to one of the assertions in the article
Trump _should_ set a good example by wearing a mask. BUT since he and his team are being tested daily, and anyone who meets him needs to do a COVID-19 test, I doubt that his failure to wear a mask is posing much risk to himself or the people around him? cnbc.com/2020/05/07/cor…