一时间，全社会感染新冠的人数迅猛上升。环顾周围，到现在还能保持阴性（至少是无症状）的人已越来越少。此外，由于新冠阳性的人数持续增加，不少人甚至觉得，感染新冠已经是平常不过的事情，迟早都要感染，何况感染过后，就能正常生活，早阳早安心。

在此，我们尝试挖掘现有的医学文献，探讨一下，感染新冠以后，是否代表身体已经产生了免疫力，从此可以放飞自我，安心生活了。

首先，我们必须明白，感染新冠后，还是有可能发生第二次新冠感染的。也就是说，阳过并不等于可以安逸。

虽然说，第二次感染时大多是由另一种病毒株引起，然而，同一种病毒株同样可以造成二次感染的发生，但约占不足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】

两次感染新冠的症状严重程度是否会有差异？有研究统计后发现68.8%的人群两次感染的严重程度相近，18.8%第二次感染时症状明显加重，而12.5%在第二次感染时症状反而更轻。

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】

感染新冠后，你离第二次感染有多远呢？有文章总结了来自全球20个国家50篇关于新冠再次感染的研究报道。通过总结118例二次感染的案例，发现第二次新冠感染最快可以发生在第一次感染后的19天，而最长的发生在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】

感染过新冠病毒后，机体已经产生过抗体，是否代表疫苗接种已经没必要了呢？一篇针对美国肯塔基州居民的研究发现，没有接种新冠疫苗的居民，发生新冠再次感染的概率，要比完成疫苗接种的居民高2.34倍。这说明，即便曾经感染过新冠病毒，依然建议进行疫苗接种，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】