A.降低傳播疾病的風(fēng)險(xiǎn)B.產(chǎn)生群體免疫C.促進(jìn)國(guó)際旅行D.提高社會(huì)經(jīng)濟(jì)效益
A.接種時(shí)間不當(dāng)B.疫苗儲(chǔ)存不當(dāng)C.個(gè)體免疫系統(tǒng)狀況差D.疫苗成分的改變