While in Africa doing epidemiological research, Joseph McCormick, author of Level 4: The Virus Hunters of the CDC, noted that whether it was hanta viruses or the then-unidentified and untreatable Ebola virus, there were people exposed to these diseases whose bodies produced antibodies and who did not get sick.
《第四級病毒》作者在非洲做流行病調查時便曾發現，無論是當時不明原因、不知如何治療的依波拉、漢他…… 等等病毒，都有感染者因體內產生抗體而未發病。