NEW YORK (AP) — A new analysis of blood samples from 24,000 Americans taken early last year is the latest and largest study to suggest that the new coronavirus popped up in the U.S. in December 2019 — weeks before cases were first recognized by health officials.
Source: More evidence suggests COVID-19 was in US by Christmas 2019 | NewsNation Now
An earlier study found antibodies present in U.S. blood samples by mid-December 2019.
This implies Covid-19 was circulating in the U.S. for about 3 1/2 months before we began to “lock down”. By comparison, it appears New Zealand locked down within about 2 weeks of their first detected case. Which may explain why there have been such different outcomes between the two countries. Lock downs need to occur immediately to have a long term effect, otherwise all they do is, at best, delay the process.