Sorry if this has been asked before re reinfection

[Captaindobbin]

If having had covid doesn’t mean you can’t get it agin then how does the vaccine work?
I thought that was broadly how vaccines worked?!
If anyone could help me understand this I’d be most grateful as my brain is having a meltdown with this whole situation.

[Redpurplegreen]

Possibly similar to a flu vaccine which is altered each year.

[PuzzledObserver]

Firstly, the WHO haven’t said getting it doesn’t mean you can’t get it again. They have said there is no clear evidence that getting it means you can’t get it again. We urgently need to do studies to find out the answers:

1. what proportion of people, having had Covid, develop antibodies, T-cells, or both;
   2). Does that vary with age, sex, or anything else you can think of
   
2. If these antibodies and T cells are developed, what degree of protection do they confer?
   
3. How long does it last?
   
   These things all vary among the immune response to other viruses, and we don’t yet know where Covid-19 will sit in this constellation.
   
   Secondly - not an expert here, but I read that the immune response produced by a vaccine is generally stronger and more long-lasting than that produced by catching the disease.
   
   Part of the trial process for the candidate vaccines will be to determine how many times/how often it needs to be given to maintain immunity. If we’re lucky, it could be one shot gives immunity for 10 years, or even for life. If unlucky, it might be course of three shots now then an annual booster. If very unlikely, we won’t be able to find a safe vaccine that works.

[CustardySergeant]

I was about to start a thread asking the same question! I've got BBC News on TV at the moment www.bbc.co.uk/news/live/world-52424263 and when they said that there's no evidence that recovering from covid-19 gives immunity I also thought "Well how can a vaccine work then?" I'm pessimistic at the best of times, so you can imagine what a miserable sod I am at the moment! It all sounds so sodding hopeless, doesn't it?

[mindutopia]

I don't think anyone has the answer for this yet. There was some evidence early on (I don't know what's happened with that since) of people testing negative...and then testing positive again weeks later. It's hard to know if that was an issue of them still being infected and actively having the virus (but the testing wasn't working right). So maybe they had always been positive, but the first test was a false negative. It's also possible that the second test could have been a false positive. It's also possible for contamination of samples to occur, especially in a community testing scenario that is fairly chaotic, lots of people working long hours and making mistakes, instruments not properly cleaned, etc. Labs produce errors in results all the time, so who knows?

But it's also possible that someone could have be re-infected. We know it's possible to become 're-infected' by multiple strains of all kinds of infectious diseases, so it's certainly possible it could happen with covid. Maybe you have immunity to strain A but then you got exposed to strain B, so maybe that wasn't enough to make you sick (you have partial immunity because of strain A), but you might still test positive. Maybe you could also get sick with multiple strains, one after the other.

In terms of vaccines, this is why vaccine development is so tricky. We have some viruses we just haven't been able to create a successful vaccine for (HIV is a really good example of this). Or the 'common cold' (though that isn't just one virus). Then there are other things were the vaccine has to change as the virus mutates. The influenza vaccine is an example of this: they have to make a new influenza vaccine pretty much every 6 months (for the southern hemisphere and then the northern hemisphere) because we don't develop immunity to influenza from becoming infected with it, and the vaccine changes so frequently that the vaccine from last year won't be effective still this year.

I don't yet know if anyone knows how it will work with covid. I imagine the scientists working on the early vaccine trials have some hunches. But the current trials are just safety ones, making sure there are no serious side effects. They won't really me measuring how efficacious the vaccine is just yet.

[Incrediblytired]

I think it’s literally that there’s no evidence and there’s no evidence because no one has had the time to do the studies that become evidence.

[mm684]

There was a professor of vaccinology on the news the other day who explained this. The coronavirus family of viruses do not leave people with much immunity or for any length of time. Vaccines developed from the same family of viruses do have a strong immunity which lasts.
In short, if you've had it you can get it again.

[PuzzledObserver]

because we don't develop immunity to influenza from becoming infected with it,

That’s not true. The issue with influenza is that it is constantly mutating and there are always new variations emerging which is why the vaccine has to be continually reformulated. But having been exposed to one version of flu may well provide some immunity to new ones which are closely related to it. This was the case with swine flu - younger adults were much more affected than older adults, because the older adults had been previously exposed to similar strains in the past and so did not suffer as bad a disease from swine flu.