iirc the Astra Zeneca COVID vaccines were less effective than the others because they used an older and more established method which is also widely used in flu

iirc the Astra Zeneca COVID vaccines were less effective than the others because they used an older and more established method which is also widely used in flu vaccines, and also used in the COVID vaccines made in China/Russia. I would assume the issue is in Astra Zeneca's manufacturing process. My friend who follows virology closely also avoids that brand now.