以色列大型研究报告发现，新冠自然免疫的效果很强 （1 in a 1,000），现在美国疫苗，感染双轮驱动，应该很快就会达到群体免疫的程度。
COVID reinfection hits 1 in a 1,000, variants may fuel it, Israeli study finds
Largest study in world followed about a fifth of COVID-positive Israelis after recovery, and found 154 got reinfected, indicating immunity is high but far from absolute