https://www.nytimes.com/2021/06/28/health/mixing-pfizer-astrazeneca-results.html
https://www.forbes.com/sites/kimberleespeakman/2021/07/26/mixed-astra-zeneca-pfizer-vaccine-boosts-covid-antibody-levels-korea-study-finds/?sh=4c8a2ea312a8
mixin astra mũi một, với pfizer mũi hai tăng hàm lượng...