https://tinyurl.com/f6325t4s
https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/recommendations-use-covid-19-vaccines/summary-statement-june-17-2021.html
加拿大国家免疫咨询委员会（NACI）与昨日（17）正式建议
For second doses, NACI recommends that:
An mRNA vaccine is now preferred as the second dose for individuals who
received a first dose of the AstraZeneca/COVISHIELD vaccine, based on
emerging evidence of a potentially better immune response from this mixed
vaccine schedule and to mitigate the potential risk of VITT associated with
viral vector vaccines.
如果你第一针打了az或者印度产covidshield疫苗 根据现有的科学依据
以及避免疫苗引发的血栓（VITT：Vaccine-Induced Immune Thrombotic Thrombocytopenia）
推荐在第二针施打mRNA疫苗 取代原本的计划（即施打原本疫苗的第二剂）
大概4这样