Thread by @bencowling88

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)

https://twitter.com/tripperhead/status/1371632154732503040

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)

I think it is appropriate for testing to disregard prior infection or vaccination status because we know people who have been previously infected, or vaccinated, can still be infected again. It’s also possible to detect prolonged shedding in some infected persons (4/17)

If a person tests positive for #COVID19 in Hong Kong, even if they are asymptomatic, they are admitted to an isolation ward in a regular hospital or a field hospital until they are judged to have recovered (5/17)

Recovery could be quicker for vaccinated persons, but I think there is no reason that vaccinated-but-still-infected persons should be exempt from isolation. They may still be infectious, and they are in the best place if medical attention is needed (6/17)

The Department of Health in HK traces the contacts of known cases, as a targeted approach to reduce onwards transmission in the community. Close contacts, with the highest chance of having been infected, are placed in quarantine for 14 days since their most recent exposure (7/17)

If a person tests positive after entering quarantine, the walls of the quarantine facilities will prevent any onwards transmission in the community that would otherwise have occurred. Currently I think around 5% of quarantined contacts ultimately test positive (8/17)

My colleagues and I have estimated that contact tracing and quarantine is reducing transmission in Hong Kong by around 25% - not enough to prevent epidemic waves as we have seen repeatedly over the past year - but an important contribution (9/17)

If we didn’t use this type of targeted approach, we might need more drastic social distancing measures like have been seen elsewhere in the world (10/17)

If a close contact has been fully vaccinated, their risk of infection after exposure drops substantially, and there would not be as much effect on transmission of placing fully-vaccinated-close-contacts in quarantine. Particularly if they received the BioNTech vaccine (11/17)

We know the Sinovac vaccine is very good at reducing the risk of severe illness or death if a breakthrough infection occurs, but it only has a moderate effectiveness of around 50% against mild infection, and mild infections can be contagious (12/17)

It is not too surprising that mainland China has not yet announced a shorter quarantine duration for arriving travelers who have received mainland-produced vaccines like Sinovac, perhaps because it would be too much of a risk? (13/17)

The incentive for receiving a mainland-produced vaccine being presented in this article is only an easier visa application process (14/17)
nytimes.com/2021/03/12/wor…

The BioNTech vaccine is much more effective, likely more than 90% effective against mild infections, meaning a close contact who was fully vaccinated w/ BioNTech might have on average less than a 0.5% chance of being infected rather than a 5% chance (15/17)

Perhaps close contacts who have received BioNTech could be placed under medical surveillance, and required to be tested multiple times during the 14 days since exposure, but could avoid being sent to a quarantine camp. (16/17)

How about quarantine-free arrival for fully-vaccinated travelers coming to Hong Kong? That will be unlikely until we reach a high level of population immunity (see article), and will be the topic of a later thread (17/17)
news.mingpao.com/pns/%E8%A7%80%…