有效疫苗產生可以防止醫學意義的感染(infection),但是預防感染的比率和預防得病的比率不一樣,免疫反應(細胞和體液免疫)抑製或消除病原體在體內的繁殖,得病或不得病取決於病原體的數量和身體的反應程度。
由此帶來的說法就會不同,譬如,新冠疫苗防止了生病 ,如果不能防止進入的話, 能不能防止無症狀感染?答案是肯定的,體內病毒的數量可以有三種情況:
1)少到忽略不計(一進入就被殺死);2)存在一定數量而不致病(無症狀感染);3)致病(數量很大)。
疫苗引發的抗體或者細胞免疫可以不同程度地抑製體內病毒數量,但能否減少“侵入”呢?我傾向認為可以。因為身體有幾道防禦陣線,就呼吸道表麵來說,抗體IgA就存在於呼吸道表麵。
IgA 不僅在血清中可測到,大部份的分泌物如眼淚、汗水、唾液、乳汁等,也都含有 IgA。通常這些分泌出來的 IgA 更能有效保護粘膜組織,防止細菌或病毒的侵犯。
The types of antibodies are:
- Immunoglobulin A (IgA): It's found in the linings of the respiratory tract and digestive system, as well as in saliva (spit), tears, and breast milk.
- Immunoglobulin G (IgG): This is the most common antibody. It's in blood and other body fluids, and protects against bacterial and viral infections. IgG can take time to form after an infection or immunization.
- Immunoglobulin M (IgM): Found mainly in blood and lymph fluid, this is the first antibody the body makes when it fights a new infection.
- Immunoglobulin E (IgE): Normally found in small amounts in the blood. There may be higher amounts when the body overreacts to allergens or is fighting an infection from a parasite.
- Immunoglobulin D (IgD): This is the least understood antibody, with only small amounts in the blood.