I'm speculating, could be way off. But I think as people get infected then we'll be resistant to it. Eventually we'll get to the point where it isn't nearly as lethal or infectious.
Those people that do get infected apparently do develop an immunity for at least a few years.
I don't know that anyone is suggesting that this immunity can be transferred from person to person.
So if no vaccine is developed it is not unlikely that enough will be infected for the rate to naturally fall off.
At a guess that could mean somewhere around 60% becoming infected and that's not far off the governor of California's prediction.
But who knows? Ask an expert.
I think its this 'herd immunity' is what people think will provide protection for others. But I'm still skeptical
"This 'herd immunity'" is what stops very many unvaccinated against, say measles, from getting infected and the level of infected (or vaccinated ones) depends on the R0 value.
For Covid-19 R0 is about 2.2, for influenza 12 and for measles about 18. See:
Epidemic theory (effective & basic reproduction numbers, epidemic thresholds)
Herd immunity
Herd immunity occurs when a significant proportion of the population (or the herd) have been vaccinated (or are immune by some other mechanism), resulting in protection for susceptible (e.g. unvaccinated) individuals. The larger the number of people who are immune in a population, the lower the likelihood that a susceptible person will come into contact with the infection. It is more difficult for diseases to spread between individuals if large numbers are already immune as the chain of infection is broken.
The herd immunity threshold is the proportion of a population that need to be immune in order for an infectious disease to become stable in that community. If this is reached, for example through immunisation, then each case leads to a single new case (R=1) and the infection will become stable within the population.
If the threshold for herd immunity is surpassed, then R<1 and the number of cases of infection decreases. This is an important measure used in infectious disease control and immunisation and eradication programmes.
Note that "If the threshold for herd immunity is surpassed, then R<1 and the number of cases of infection decreases" but does not fall to zero!
If I am immune to the virus, it doesn't mean I cant spread it. It simply means I wont catch it.
If I took a bus and an infected person sneezed on their hand and then pushed the stop button or held the rails and then I did the same and then proceeded to go home and without washing my hands, touched the door handles, light switches TV remote etc, a non immune person can catch it.
It just means I wont get sick and sneeze/breathe it out places.
Yes, you can still pass on virus contamination but the virus won't multiply and make you a spreader.
You need a large chunk of the population to all be immune to make a substantial impact. For vaccine preventable diseases I believe the target rate is 95%.
The above Herd Immunity Threshold is just that, a threshold past which the "the number of cases of infection decreases" but does not fall to zero.
That target rate of 95% fits for measles where R0 = 18. For the Covid-19 it would be about 55% but with Covid-19 maintaining a higher level would be highly desirable.
But with so many anti-vaxxers around it is hard to get vaccination rates above 90%.
So like it or not the infection level will head towards 55% until a vaccine is developed and unless anti-viral drugs or some other treatment is developed probably 3% of those infected will die.
The disease is unlikely to die out until a far higher vaccination rate is achieved.
So says a non-extert anyway.