一時間，全社會感染新冠的人數迅猛上升。環顧周圍，到現在還能保持陰性（至少是無症狀）的人已越來越少。此外，由於新冠陽性的人數持續增加，不少人甚至覺得，感染新冠已經是平常不過的事情，遲早都要感染，何況感染過後，就能正常生活，早陽早安心。
在此，我們嘗試挖掘現有的醫學文獻，探討一下，感染新冠以後，是否代表身體已經產生了免疫力，從此可以放飛自我，安心生活了。
首先，我們必須明白，感染新冠後，還是有可能發生第二次新冠感染的。也就是說，陽過並不等於可以安逸。
雖然說，第二次感染時大多是由另一種病毒株引起，然而，同一種病毒株同樣可以造成二次感染的發生，但約占不足5%。
Serology was performed in 64 patients, of whom 39 (60.1%) had antibodies against SARS-CoV-2 when sampled at the early stage of their second infection. Only seven patients (3.4%) were infected twice with the same variant.
【Emerg Microbes Infect. 2022 Dec;11(1):894-901. doi: 10.1080/22221751.2022.2052358. SARS-CoV-2 reinfection and COVID-19 severity】
兩次感染新冠的症狀嚴重程度是否會有差異？有研究統計後發現68.8%的人群兩次感染的嚴重程度相近，18.8%第二次感染時症狀明顯加重，而12.5%在第二次感染時症狀反而更輕。
Many cases are lacking genomic data of the two infections, and it remains unclear whether they were caused by different strains. In the present study, we undertook a rapid systematic review to identify cases infected with different genetic strains of SARS-CoV-2 confirmed by PCR and viral genome sequencing.
Overall, 68.8% (11/16) had similar severity; 18.8% (3/16) had worse symptoms; and 12.5% (2/16) had milder symptoms with the second episode. Our case series shows that reinfection with different strains is possible, and some cases may experience more severe infections with the second episode. The findings also suggest that COVID-19 may continue to circulate even after achieving herd immunity through natural infection or vaccination, suggesting the need for longer-term transmission mitigation efforts.
【J Investig Med. 2021 Aug;69(6):1253-1255. doi: 10.1136/jim-2021-001853. Epub 2021 May 18. COVID-19 reinfection: a rapid systematic review of case reports and case series】
感染新冠後，你離第二次感染有多遠呢？有文章總結了來自全球20個國家50篇關於新冠再次感染的研究報導。通過總結118例二次感染的案例，發現第二次新冠感染最快可以發生在第一次感染後的19天，而最長的發生在293天。
This study included 50 studies from 20 countries. There were 118 cases of reinfection. Twenty-five patients were reported to have at least one complication. The shortest duration between the first infection and reinfection was 19 days and the longest was 293 days.
The public, including rehabilitated patients, should be fully vaccinated, wear masks in public places, and pay attention to maintaining social distance to avoid reinfection with the virus.
【Glob Health Res Policy. 2022 Apr 29;7(1):12. doi: 10.1186/s41256-022-00245-3. Reinfection in patients with COVID-19: a systematic review】
感染過新冠病毒後，機體已經產生過抗體，是否代表疫苗接種已經沒必要了呢？一篇針對美國肯塔基州居民的研究發現，沒有接種新冠疫苗的居民，發生新冠再次感染的概率，要比完成疫苗接種的居民高2.34倍。這說明，即便曾經感染過新冠病毒，依然建議進行疫苗接種，以降低第二次新冠感染的概率。
Kentucky residents who were not vaccinated had 2.34 times the odds of reinfection compared with those who were fully vaccinated (odds ratio [OR] = 2.34; 95% confidence interval [CI] = 1.58-3.47). These findings suggest that among persons with previous SARS-CoV-2 infection, full vaccination provides additional protection against reinfection. To reduce their risk of infection, all eligible persons should be offered vaccination, even if they have been previously infected with SARS-CoV-2.
【MMWR Morb Mortal Wkly Rep. 2021 Aug 13;70(32):1081-1083. doi: 10.15585/mmwr.mm7032e1. Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination - Kentucky, May-June 2021】
