Posted by a scientist friend, permission to cut-and-paste. I found it both informative and helpful.
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“When we were kids, we were taught that certain childhood diseases were things you “only got once”. That wasn’t 100% true of course — we all knew someone who got Chicken Pox twice — but it was true most of the time. The reason of course was that you build immune memory (antibodies, B cells and T cells) that would kill or suppress the virus when you encountered it again. In the case of Chicken Pox, this would also suppress the virus lying dormant in your nerves for life!
Even so, without always knowing it, you were getting boosted. Maybe you got your booster in the form of a vaccine every 5 or 10 years. Maybe you got your booster in the form of an asymptomatic or mild infection from a child with Chicken Pox in the community, in the days before that vaccine was common. These periodic exposures kept immunity high and prevented severe illness. While some level of immunity lasts a lifetime, if you don’t encounter a pathogen periodically, that immunity will fade over time, and breakthrough infections become more likely. (This is why older people get Shingles, which is a re-activation of the dormant Chicken Pox virus in their nerves.)
What we’re demanding from our COVID vaccines is a very high level of immunity, called sterilizing immunity, in which high levels of neutralizing antibodies prevent all infection — even a positive PCR test without symptoms. Most of our vaccines don’t confer that level of immunity. Inactive Polio vaccine doesn’t even prevent infection, only severe disease!
The reason we need our antibodies to be so high is because we’re in the middle of a raging pandemic, and our fellow citizens have been largely unwilling to use engineering controls like masks to keep spread under control, so we need maximum protection from a vaccine. Over time, as the virus hopefully weakens and becomes endemic — and as more of us have some degree of immunity from either vaccination or past infection — this will be less necessary. Most people will be “boosted” through periodic exposures that feel like a common cold (or nothing), and we may also need occasional vaccine boosters (but not every 6 months as I hear some people guessing). Our vaccine-induced immunity will continue to provide protection against severe illness for years to come. Because our hospitals won’t be in danger of going over capacity from covid, it will be less important to prevent every infection. We will still need to find ways to protect immunocompromised and medically vulnerable people. This will be easier when case numbers are lower and our healthcare system isn’t under so much strain.
tl;dr don’t necessarily extrapolate from the current vaccine situation to the long term. Things will stabilize. Pandemics *do* end.”