如果打一针 P 或者 M疫苗后就像文中说得这么有效，难道真有必要冒着更大副作用的风险打第二针吗？

https://www.businessinsider.com/covid-vaccine-one-shot-effectiveness-pfizer-moderna-astrazeneca-vaccines-dose-2021-3

Evans said there was "pretty clear evidence" that you get at least 80% protection — and "probably" better than 90% — for Pfizer's vaccine against COVID-19 with symptoms after a single dose. He said you couldn't be absolutely sure what happens after 21 days because it hadn't been fully tested.

you get at least 80% protection — and probably better than 90% — for Moderna's vaccine against COVID-19 with symptoms after a single dose for 28 days. After 28 days it was unclear because it hadn't been tested．

觉得一针的实际效果应该测一下，特别是超过21天（Pfizer), 或者28天(Moderna) 以后，因为一针的好处实在太多太多了……