[akiddoc]

I wonder whether 15 or so years of doing annual flu shots, each different from the others, might provide some measure of protection?

Almost definitely not. Different family of viruses with very different surface proteins. The only real similarity is that both are RNA viruses, which doesn't mean much.

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There are seven known coronaviridae that affect humans.  Four of them cause symptoms of the common cold; the other three are SARS, MERS, and COVID-19.  SARS and MERS have been kept under control, so we have never had a chance to see if someone gets it twice.  There are anecdotes of people getting COVID-19 twice, but so far there hasn't been enough time to see if immunity wanes in the majority of patients.  However, the four coronaviridae that cause common cold symptoms do not induce long lasting immunity and it is possible to become re-infected.

One other comment; if exposure to the four coronaviridae that produced the common cold was protective, you would expect newborns and young children to be particularly vulnerable to COVID-19, since they are least likely to have been exposed to other coronaviridae.  In fact, the youngest patients have the lowest mortality.

There is a possibility that prior exposure to one of the other coronaviridae produces non-neutralizing antibodies that makes it easier to become infected by COVID-19 through a mechanism called ADE (antibody-dependent enhancement).  A second theory is that you get some T cell immunity from prior exposure to one of the other coronviridae, but unfortunately it contributes to cytokine storm and the inflammatory response and is what makes some people much sicker.

BC

Not necessarily. Daycare aged children catch 6 to 8 viruses a year. They are much more likely to have contracted a recent respiratory virus than an adult. They most likely have higher antibody levels to Coronaviruses than their parents or grandparents, although I don't think much is known about T-cell immunity longevity with these viruses. 

Personally, I don't think that is the reason that kids have such low morbidity. I think it is the general lack of primed inflammatory pathways in children vs adults that accounts for the difference. A lot of the aging process seems to be aligned with inflammatory processes. Adults are already more likely to start an inflammatory cascade when they first encounter Covid-19.

[akiddoc]

I wonder whether 15 or so years of doing annual flu shots, each different from the others, might provide some measure of protection?

Almost definitely not. Different family of viruses with very different surface proteins. The only real similarity is that both are RNA viruses, which doesn't mean much.

---

There are seven known coronaviridae that affect humans.  Four of them cause symptoms of the common cold; the other three are SARS, MERS, and COVID-19.  SARS and MERS have been kept under control, so we have never had a chance to see if someone gets it twice.  There are anecdotes of people getting COVID-19 twice, but so far there hasn't been enough time to see if immunity wanes in the majority of patients.  However, the four coronaviridae that cause common cold symptoms do not induce long lasting immunity and it is possible to become re-infected.

One other comment; if exposure to the four coronaviridae that produced the common cold was protective, you would expect newborns and young children to be particularly vulnerable to COVID-19, since they are least likely to have been exposed to other coronaviridae.  In fact, the youngest patients have the lowest mortality.

There is a possibility that prior exposure to one of the other coronaviridae produces non-neutralizing antibodies that makes it easier to become infected by COVID-19 through a mechanism called ADE (antibody-dependent enhancement).  A second theory is that you get some T cell immunity from prior exposure to one of the other coronviridae, but unfortunately it contributes to cytokine storm and the inflammatory response and is what makes some people much sicker.

BC

Not necessarily. Daycare aged children catch 6 to 8 viruses a year. They are much more likely to have contracted a recent respiratory virus than an adult. They most likely have higher antibody levels to Coronaviruses than their parents or grandparents, although I don't think much is known about T-cell immunity longevity with these viruses. 

Personally, I don't think that is the reason that kids have such low morbidity. I think it is the general lack of primed inflammatory pathways in children vs adults that accounts for the difference. A lot of the aging process seems to be aligned with inflammatory processes. Adults are already more likely to start an inflammatory cascade when they first encounter Covid-19.