“I want vaccines to have been given to all residents who want to receive them by the October-November period,” Japanese prime minister Suga Yoshihide said in a parliamentary debate on Wednesday, June 9, 2021. He also estimated, the grand total of doses could “exceed at least 40 million by the end of this month.”

As of June 8 the count on the Prime Minister’s Office (Kantei) website stood at 19.4 million doses, so to hit 40 million doses by the end of June requires a little more than 900,000 a day (20.6 m doses in 22 days). From the published numbers it looks like we may already be in that vicinity for the daily rate.

Even though the number of doses per day for residents age 65 and above (“koreisha”) for the most recent date added is still coming in at under 500,000 the day it’s released, but many of the local counts arrive delayed. The daily counts will later increase through daily retroactive updates. By the time all numbers for a given date have trickled in over the course of several weeks, the total often doubles. For example, the May 30 “koreisha” total was originally released as 200,187 but within 10 days it had grown to 405,165.

Let’s do a quick back of the envelope calculation to see if the projection for vaccinating all adult residents of Japan who want to get vaccinated by the end of November is realistic.

If they hit 40 million doses by end of June (which as I mentioned above requires an average of 900,000 doses a day until then) and we take a figure of 110 million adults of a a population of 126 million: assuming 80 percent of them would opt to get vaccinated, we end up with 88 million people times two doses per person, i.e. 176 million doses. Subtracting 40 million done by the end of June leaves 136 million doses to be injected between July and November (5 months). Divide the total by the roughly 150 days and it becomes clear that if they maintain about 900,000 a day for the next half a year they will indeed be done by the end of November.

However this ignores that the vaccinations are proceeding at vastly different speeds in different cities and prefectures. All things staying the way they are, once the most efficient places are done (which would happen before November) and only the laggards remain in the race, the 900,000 a day average would no longer be sustained. So the key will be to speed up the places that are lagging behind others right now.

How realistic is the 900,000 a day goal if daily vaccine counts still pop up on the Kantei website at less than 500,000? What’s the real number right now?

We can make a rough guess of what percentage of the actual daily vaccinations are represented in the initial count that gets published for a given date by looking at past data.

For example, the count for June 9 published today (June 10) for 65+ is 474,484. The actual number is likely to be over a million, as I’ll explain below. The published number is a partial count, as only about 50 percent of the vaccinations are reported via VRS (Vaccine Recording System) within one day. The rest arrives later. Another 10 percent or so arrive the next day, then another 5 percent, etc, etc until we get to over 99 percent of the total after a month or so.

I looked at the 28 days ending on June 8 and how they had changed on June 10 vs. June 9 in the Excel spreadsheets. They increased by factors of 1.0015 to 1.1845. Multiplying all these increases by each other to get the cumulative 28 day growth yields a factor of 2.27.

I repeated the same exercise for one day earlier, i.e. 28 days ending on June 7 and their change between June 9 vs. June 8. The daily increases range from 1.0058 to 1.1885. Multiplying 4 weeks’ worth of increases gives a factor of 2.47.

If we apply the lower of these factor values to today’s addition, on the assumption that the spread of what percentage of reports comes in after how many days is consistent, that would suggest an actual figure of 1.08 million vaccinations of residents 65+ done yesterday whose total count will be known by July 7 (after 28 days of reports still arriving). That’s on top of another 160,000 or so vaccinations of healthcare workers, by the way.

While it’s disgraceful that we have to figure out the state of the campaign so indirectly (because of a broken IT system built using 385 million yen of our taxes), this exercise at least gives us a good guess of how things are really going.

On that basis I’d say the government’s outline is plausible: Japan is likely to reach a goal of 40 million doses deployed by the end of June and full vaccination of willing adults by the end of November.