We don't have evidence due to disease being so new, but there's enough reason to suspect we'll develop at least short term neutralizing immunity.
But yes, caution is necessary. We don't have enough evidence to push forward a national strategy that's based on people developing immunity without a vaccine.
What's worrisome is that some people are testing positive again, after being diagnosed as positive. Crew on the CVN-71 Roosevelt have tested positive, been quarantined for 14 days, then tested negative twice (two days apart), but then still testing positive a few days later.[1]
The possible scenarios for this I can come up with are:
1. No immunity after initial infection
2. Bad test methodology (contamination etc)
3. Bad tests. The article doesn't mention the test type, so perhaps they were initially misdiagnosed (false positive), then infected upon return to the ship. The implication from this would be that the virus is still prevalent in the crew on board the Roosevelt...
In South Korea, they discovered that all of the many potential reinfections they had detected were due to faulty (overly sensitive) tests. There are no confirmed cases of reinfection and many thousands of people on 'front line' jobs who have recovered form the disease, returned to work and never been reinfected. In a study done on monkeys, scientists were unable to achieve reinfection.
Risk vs reward. If there is immunity, then developing herd immunity sooner rather than later is important (even more so if there's immunity but it's only short-term). If there's no immunity, we're, excuse the expression, fucked anyhow.
Can vaccines even be developed if there's no natural immunity?
If there is short term immunity yes (diphteria, tetanos is an example, polio too).
Being exposed to the same antigen while you have an immunity should reactivate this immunity, that's a reason why a "herd immunity" tactic could work, at least for a time
However if the natural immunity w/o reactivation only last a year or less, you will end up with a new outbreak at the end of the period. And if the immunity period is shorter than the recuperation one, you will have a virus that will be a lot more lethal.
But yes, caution is necessary. We don't have enough evidence to push forward a national strategy that's based on people developing immunity without a vaccine.
Here's WHO's statement on this matter:
https://www.who.int/news-room/commentaries/detail/immunity-p...
"Herd immunity" without a vaccine, as a strategy, is equivalent with doing nothing and let the virus wreak havoc on the population.