The majority of votes on HN I believe are instinctive - someone liked or didn't like what you said, or the tone or whatever and that's it. Often there isn't much rhyme or reason.
Clearly there are low/high value comments, or flame-wars but generally that's not it.
Apparently, PG himself was fond of voting for disagreement/agreement, but even he I don't think quite has seen the degree of arbitrary voting.
You will notice that people in the moments after your comment are much more likely to hate on it arbitrarily than later on when you might see some upswing.
If you comment on anything even remotely controversial, that even hints at something like Brexit, EU nationalism, Transgender etc. - expect to see a lot of volatility. It's really quite an interesting phenom to see.
Frankly it's pointless to meander about it and after much speculation I would say just don't worry about it - and - don't put too much stock in any kind of 'points system' it really doesn't matter that much at all.
The Oxford vaccine is doing well, the UK is way ahead due to the locality of it all, which is great, because they need the help what with having a considerably higher death reate.
I would recommend you see here [1] for a really good breakdown of vaccination and other COVID data.
[1] https://ourworldindata.org/covid-vaccinations