Icosian Reflections

…a tendency to systematize and a keen sense

that we live in a broken world.

Which vaccine?

I wrote in January about vaccines and public health, and I wanted to retract my bottom-line recommendation about which vaccine to get -- if you have a choice -- in Hong Kong. Appointments opened to residents 16+ yesterday, so this post is coming a bit late, but oh well. Here we are.

If you're in Hong Kong and have choices, my personal recommandation is that you get an appointment for the BioNTech (Pfizer) vaccine as soon as possible. (If you are in Hong Kong and have a HKID, the link to book a vaccine in English is here -- click the red "Book Vaccination" box at the left.)

In the rest of this post, I'll describe how my thinking has changed on the argument I expressed in my January post.


When I wrote in January, I was looking at a massive shortfall in vaccine demand in the US and assuming that it couldn't happen here in Hong Kong. In hindsight, I was extremely wrong.

In the first 57 days of the government vaccination program, 16.3 doses have been given for every 100 persons in Hong Kong, at an average rate of 21,500 doses/day (government source). On Friday at 9am, all residents 16+ became eligible to book appointments, and "about 31,300 new vaccination bookings [were] made online" in the 13 hours before and 11 hours after the opening. I'm not sure whether this is 31k people with 62k appointments, or 16k people with 31k appointments.

Even if it's 62k new appointments in the first-day rush, that's still only 2.4x the daily processing rate (26,100 doses given in the same 24 hours) and I am confident it will fall off siginificantly in the next report. On current margins, Hong Kong is very far from booking enough appointments to fill capacity, and so you going out to get an appointment is extremely unlikely to bump anyone from a spot they would have taken. So, first things first -- even if you're low-risk, getting vaccinated now when the city is under-using its capacity is an efficiency win.

The argument that I made last time about choice of vaccine was that Sinovac-specific hesitancy would mean that BioNTech would be over-demanded and Sinovac under-demanded. Given the weakness of overall demand and the relatively robust Sinovac takeup so far, I don't think that's a worry on current margins.

While it's true that just over 60% of vaccine-getters have opted for the Pfizer-made vaccine, it would take 100 more days (at an optimistic 31k people per day) to book all of the 7.5mln BioNTech doses Hong Kong has secured. If the Sinovac takeup halves, that would mean HK running out of Pfizer vaccines around August 2, having vaccinated just over 61% of the population. Another 12% of the city is under 14, and we'd be entering the range of Youyang Gu's estimates of "herd immunity". That's a wildly optimistic set of assumptions, and I expect that in reality demand for both vaccines (but relevantly, of Pfizer-BioNTech) will taper off long before then.


So electing for BioNTech instead of Sinovac won't cause fewer vaccinations across Hong Kong. What's the upside?

Well, it appears to be a materially better vaccine. Wikipedia (ret. 2021-04-24) suggests that CoronaVac has around 80% efficacy at preventing hospitalizations and deaths, with around 51% efficacy (+/- 15%) at preventing any symptoms. If we could give everyone a 51% reduction in symptoms and a 80% reduction in hospitalizations, that would be a huge deal -- because, as I said before, vaccination isn't for you and enough reduction in transmission to keep \(R < 1\) is enough, even if it isn't perfect.

But Pfizer's vaccine, per Wikipedia has an efficacy in the high 90s for symptoms, hospitalizations, and deaths. It's kind of obviously better, and (as a friend pointed out to me) there isn't a lot of room for mix-and-match to do much better than the double-dose that Hong Kong is insisting on.

I don't think anyone has hard numbers on reduced infectiousness, but there's every reason to believe that the vaccine that's superior at the other endpoints will be better at it as well.


It's basically as simple as that -- there isn't enough demand that it's worth letting others go first, and it doesn't look like there's enough Sinovac hesitancy (and there is enough BioNTech capacity) that it's worth electing for CoronaVac in order to reserve some CoronaVac for others.

If you are in Hong Kong and have a HKID, the link to book a vaccine in English is here -- click the red "Book Vaccination" box at the left. My first dose is on Monday!