得过新冠还打疫苗么？
CDC 以前的指南是：得了新冠，病愈90天后再打疫苗。
现在的指南则含糊其词（见附注），令人摸不着头脑。
其实，感染过，无论轻重还是无症状，都相当于打了一针疫苗。从人体免疫学角度，在数月后再打一针，就能起到强化（boost)作用。实在没有必要打第二针疫苗。
按以往个体疫苗注射的规程，应该是：
1. 测试。阳性，不打；阴性，往下走。
2. 按程序接种。
3. 测试。阳性，说明疫苗起作用了；阴性，要查明原因，是受者体质或疾病影响了疫苗，还是疫苗失效。如果是后者，
4. 换疫苗批号，再次接种。
5. 测试。阳性，说明前次接种疫苗或过程有问题；阴性，此人不适合该种疫苗，或免疫系统有问题，需进一步就医。
现在所进行的大规模群体接种新冠疫苗，不可能对每一个人做具体分析测定。
只能自己想办法：
在打疫苗之前，测一下抗体。如阴性，打；如强阳性，不打； 如弱阳性，只打第一针。
打过第一针后，在第二十天左右再测抗体。
如强阳性，说明以前有感染，但体內抗体水平太低测不到，但记忆细胞迅速动员，产生大量抗体。这种情况不适合打第二针，要是坚持打下去，反应会很严重，对身体不好、有重病的个体，也许难以承受。
如阴性，可能第一针有问题，请接打第二针。另外，极少数人（约占人群的1%）有免疫缺陷，无法诱导出抗体。
如弱阳性，正常。请接打第二针。
打过第二针后一个月，应该是抗体水平最高的阶段。如果有可能，请再测一次抗体。如果有人还是阴性，不要感到意外。请与CDC联系，会有专家解答，或调查。
我个人是按上面的思路做的
在打疫苗之前测了抗体 https://blog.wenxuecity.com/myblog/73054/202012/596.html
打过第一针后，又测了一次，已经有很强的阳性了
https://blog.wenxuecity.com/myblog/73054/202102/567.html
在做了充分准备后，打了第二针 https://blog.wenxuecity.com/myblog/73054/202102/1706.html
出现了比较严重的反应 https://blog.wenxuecity.com/myblog/73054/202102/6363.html
也许应该推迟第二针接种，等数月后抗体消退时再打。
以上只是本人积于以往所学的思考，和个人情况做的选择。
仅做参考，勿照做，后果自负。
附注
https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
People with prior or current SARS-CoV-2 infection
Data from clinical trials indicate that the currently authorized COVID-19 vaccines can be given safely to people with evidence of a prior SARS-CoV-2 infection. People should be offered vaccination regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection. Viral testing to assess for acute SARS-CoV-2 infection or serologic testing to assess for prior infection is not recommended for the purposes of vaccine decision-making.
Vaccination of people with known current SARS-CoV-2 infection should be deferred until the person has recovered from the acute illness (if the person had symptoms) and they have met criteria to discontinue isolation. This recommendation applies to people who experience SARS-CoV-2 infection before receiving any vaccine dose and those who experience SARS-CoV-2 infection after the first dose of an mRNA vaccine but before receipt of the second dose.
While there is no recommended minimum interval between infection and vaccination, current evidence suggests that the risk of SARS-CoV-2 reinfection is low in the months after initial infection but may increase with time due to waning immunity. Thus, while vaccine supply remains limited, people with recent documented acute SARS-CoV-2 infection may choose to temporarily delay vaccination, if desired, recognizing that the risk of reinfection and, therefore, the need for vaccination, might increase with time following initial infection.