A agree but there’s mixed evidence that we are building immunity indeed one of the concerns is that it’s a temporary immunity due to people being infected more than once in a short space of time
Yes true. There's still a question mark over this whole thing about "immunity". It's probably too early to tell, but what we can do is look what we know about building immunity to other viruses, especially ones from the same family as COVID-19, i.e. other "coronaviruses", like SARS and MERS. and we see evidence in those cases that immunity can be developed. That doesn't mean for certain that we will develop immunity to COVID-19, but put it this way, it would be extremely unusual if not.
The immunity comes from developing protective antibodies to the virus and we do that either by immunising people with a small inactive amount of the virus (i.e. a vaccine) or by contracting the infection naturally. We don't have a vaccine currently, so if we are going to develop immunity throughout the population there's only one way that's going to happen at the moment and that's through having sufficient numbers of the population contracting the infection. And this was always the plan from the outset - but it was spreading too fast, at a rate that threatened to overwhelm our ability to cope with it, so we've slowed it down through lock down and social distancing measures. The next phase is to let the handbrake off, slowly, and allow it to spread a bit more, but not to those who are at serious risk from it.
Re-infection is an interesting topic. There have been some reports of people having it more than once - however, those reports are not reliable. And the reason why they are not reliable is because no serotyping was done in these patients, so we don't know whether they contracted a new strain of the virus, or whether they never eliminated the first strain that they had. Studies of other coronavirus show that patients had immunity for over a year. Again, we don't know, but we might expect to see something similar with this COVID-19.
There's a lot of "guesswork" going on at the moment and the truth is, we just don't have all the information to know for certain about a lot of things to do with this. Most of the "data" we do have so far is based on a population of patients who were hospitalised for serious infection with COVID-19. We can look at their immunity levels, but that doesn't tell us much about the ability to develop immunity levels in the general population, especially in healthy people, who are the majority.
We have to remember that the lock down was introduced in order to slow down transmission of the virus. In the absence of a vaccine and mass immunisation programme, it is the only tool we have to stop the virus spreading so rapidly that it exhausts our ability to deal with it, i.e. the NHS services. We didn't slow it down because it was going to rip through society and kill millions of us off. The vast majority of us are at little or no risk from this virus. We slowed it down so we can better protect those who are at risk and be able to manage to deliver other important, life-saving, healthcare services. Sometimes I think this point gets overlooked - as we go around with useless face-masks on and give each other a wide berth in the open outdoors - and have our kids losing out on an education - for no good scientific reason.