In order for an infectious disease (e.g. COVID-19) to spread, the infectious agent (e.g. SARS-CoV-2) must jump from one person to another. The rate of this happening depends on the rate that an infectious person will come into contact with a susceptible person multiplied by the rate of the virus making the jump when the two people are nearby. The reproduction number R is obtained from the rate of infection spread times the length of time a person is infectious. If R is above one then a single person will infect more than one person on average and thus the pandemic will grow. If it is below one, then the pandemic will diminish. Herd immunity happens when enough people have been infected that the rate of finding a susceptible person becomes low enough that R drops below one. You can find the math behind this here.
However, a major assumption behind herd immunity is that once a person is infected they can never be infected again and this is not true for many infectious diseases such as other corona-viruses and the flu. There are reports that people can be reinfected by SARS-CoV-2. This is not fully validated but my money is on there being no lasting immunity to SARS-CoV-2 and this means that there is never any herd immunity. COVID-19 will just wax and wane forever.
This doesn’t necessarily mean it will be deadly forever. In all likelihood, each time you are infected your immune response will be more measured and perhaps SARS-CoV-2 will eventually be no worse than the common cold or the seasonal flu. But the fatality rate for first time infection will still be high, especially for the elderly and vulnerable. Those people will need to remain vigilante until there is a vaccine, and there is still no guarantee that a vaccine will work in the field. If we’re lucky and we get a working vaccine, it is likely that vaccine will not have lasting effect and just like the flu we will need to be vaccinated annually or even semi-annually.
Scientific Clearing House 
This is my impression from anecdotal ‘hard facts’. (I have been tested—came out negative –i was sort of sad because i wasted time and money of all these nurses and doctors and more –technicians, etc.and i didn’t get my disability check.) i’m fairly sure i have it but it comes and goes. (sometimes i can barely walk and have all these pains in my back, arms and neck, but then i go outside and walk a few miles and feel better.)
most people in my area –but not all–wear masks–some dont care. they arern’t trump supporters–they are ‘street people’. many people are coughing. i can’t go visit my relatives—still locked down. i think this is a good idea, i’m not bringing what ever i may have over there.
i have had recurrences of this for last 4 months—and i think i may have even had it before jan 2020. ( i almost died from the west nile virus years ago—noone believed me but one person who came to check up on me noticed i couldn’t walk. i bruned out the air conditioner—i slept in front of it—my temperature hit 110F.)
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Please keep posting on Covid as the situation progresses. It is now March 2021 and the UK is under severe lockdown. It is by no means certain that the supposed benefits of this measure outweigh the huge damage to health, wellbeing and livelihood, both short and long term. We need nuanced analysis that factors in multiple aspects and isn’t limited to a 1-dimensional approach. Good science, as it were. What I’ve seen here is encouraging, and I’ll like to read up-to-date articles.
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