But I still would like to read a answer to my original question. Would vaccinating 70% of the Indonesian population be enough to reach herd immunity, or should it be much more (100% ?). All policy in Indonesia seems to based on that hypothesis. As soon 70% is vaccinated all will be fine. I highly doubt that, but would be very happy to change my mind.
In the U.S., Dr. Anthony Fauci has shied away from naming a specific 'magic point' for herd immunity where all is well from that point on. And as you allude to mentioning the commonality of multi-generational households in Indonesia vs. more segregated social models in some places, that point may vary widely.
A big issue is what one thinks 'herd immunity' means. COVID-19 is not going the way of small pox. So, does herd immunity mean...
1.) Nobody (or almost nobody) can get the condition, and when someone does, it's a news-making surprise (likes measles in the United States)?
I don't think this is going to happen.
2.) It routinely moves through a small but substantial minority of the population, killing a small portion of them, and the rest of us don't make any lifestyle changes around it (other than maybe a vaccination shot). Those known sick with it are advised to 'stay home and drink plenty of fluids' and try not to spread it around. Most get over it...but a few don't. This is how the flu works in the United States. There's an annual death toll, but not particularly disruptive in the greater society.
This is going to happen.
Herd immunity reduces the number of people who have it, and their probability of encountering and transmitting it to a susceptible person, thus in a multi-factorial way cutting the total number of cases (particularly hospitalizations, deaths and long-term impairment cases) to something we can more conveniently deal with.
Put another way, the point of herd immunity depends in part on what body count we're willing to pay to get back to normal, plus some other factors.
COVID-19 is new and something we're not used to, plus it's killing a lot of people and straining healthcare resources. All those are reasons it's treated as a big deal. At some point, we hope to beat it down to be the 'new flu,' so to speak.
The next question is...how will annual mortality figures for COVID-19 compare to those for flu, once we're successfully into that period? Time may tell...