A study published in September, using blood samples collected in July, estimated that about 9% of the population might have had antibodies to Covid-19 by that time. (See Less Than 10% of Americans Have COVID Antibodies)
Simple calculations suggest this means perhaps 30% may have antibodies by the end of this year and 50% by early February.
Using the figure of 9%, and assuming this was through the end of July (it was actually earlier in the month), there 4,548,077 positive test cases by July 31st.
From August 1 through Dec 19th, the CDC reports an additional 13,044,683 positive test cases.
That is 2.87x more cases since July.
Multiply that by 9% (roughly the mid point of their July estimate) and we get 25.8% of the U.S. population might now have antibodies to Covid-19.
At the rate we are adding new positive test results each day, we might see another 2.5 million or so through Dec 31st.
That would put us right about 31% – or for rounding purposes, 1/3d of the U.S. population will have Covid-19 antibodies by Dec 31st.
Earlier, Dr. Scott Gottlieb, former FDA Commissioner and consultant to CNBC said he could see 30% of the U.S. having had antibodies by the end of the year – and that the effects of “herd immunity” would become apparent.
By January 21st and the new Administration inauguration, we might then be at 42% + plus perhaps 5-7% who have been vaccinated.
Basically, by the end of January, we might be at 50% having immunity – and at which case the pandemic is coming to and end.
Disclosure – I am an idiot with no health care experience and my comments are for Entertainment Purposes Only.
Limitations – this assumes that the ratio of “untested” positives to positives found through July 31st remained the same for August 1st onward. However, because of an expansion of testing, this assumption might not be correct.