system
Given the following post, respond as if you're commenting on Reddit:
human
What are some examples of viruses that do not provide immunity post infection?

All the COVID news releases saying "There's no evidence being infected provides immunity." 

I understand that it's researchers choosing their words carefully, since there's not evidence about a lot of things COVID related because it's so new; and policymakers don't want people to start thinking their immune and taking unnecessary risks.

I always thought once you had a specific virus you were immune to it until it until it mutated. I'm also not talking about colds and flus here because those are caused by several different types of viruses and have different serotypes.

So is it really possible that a viral infection could provide no immunity?
gpt
Yes, it is possible. And unfortunately, the first cases that come to mind are other human coronaviruses that cause common colds - you can be infected by the same virus every couple years. The general trend is that if it doesn't elicit a strong immune response, there is not a strong memory immune response, so virus-specific antibodies and T cells decline in the span of months.

This doesn't rule out a vaccine though. With a vaccine, you can use adjuvants to trigger a stronger immune response alongside the antigen, and provide longer-lasting memory.