Why is there no herd immunity against common cold coronaviruses?

Question

In discussions of herd immunity against SARS-CoV-2 the underlying assumption usually appears to be that the virus basically stops spreading once a sufficient percentage of the population has overcome an infection.

My understanding is that this approach does not work for the seasonal flu, for instance, because the flu virus mutates too quickly. Since coronaviruses do not mutate so quickly, herd immunity "can work" for them.

Question: Given how long common cold coronaviruses have been spreading in the human population, why does there not appear to be herd immunity against the common cold coronaviruses? To what extend can we expect herd immunity to SARS-CoV-2 if there is no herd immunity against common cold coronaviruses?

Answer 1

The following review has extensive answers to the complex of this question. They also include MERS and SARS-Cov-1 in their discussion, as there is good data on them.

Huang et al., A systematic review of antibody mediated immunity to coronaviruses: antibody kinetics, correlates of protection, and association of antibody responses with severity of disease

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7217088/

The best data comes from challenge experiments which, with common-cold CoV, are not ethically problematic. They write:

Several studies exposed volunteers to two challenges of virus, some months apart. Reed re-challenged 6 volunteers who had been experimentally infected 8–12 months previously(ref.9). On the first challenge, all 6 developed symptoms and detectable viruses and 5 of 6 experienced significant rise in titer. In the second, 0/6 experienced illness, detectable virus or significant rise in titer. Callow et al re-challenged volunteers with the same dose of coronavirus, one year apart(ref.8). Of 9 volunteers who were infected in the first exposure, 6 (67%) were infected in the second exposure. However, none of these individuals developed respiratory illness symptoms and they experienced a mean duration of detectable virus of 2 days compared to a mean of 5.6 in the initial challenge.

So, reinfection can occur even after 1 year with HCoV 229E, and this does not support the idea of herd immunity against that virus.

Note however that it is not known to date if, when reinfected after some years, you will also shed active 229E virus. If not, this would be just as good as neutralizing immunity and would support herd immunity.