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Vaccine terminology: Killed, modified live, chemically altered， https://www.agweek.com/business/vaccine-terminology-killed-modified-live-chemically-altered

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機器翻譯: 改良的活疫苗包含已被改變（減毒）的完整病原體，因此它們不會引起臨床疾病，但仍可以在動物體內感染和繁殖。動物的免疫係統識別複製病原體的存在以產生增強的免疫反應，從而消除對佐劑的需求。一般來說，改良活疫苗產生的免疫力通常比滅活疫苗產生的免疫力持續時間更長。改良活疫苗的主要優點是更廣泛的保護範圍和持續時間，因為動物暴露於複製病毒或細菌的所有階段。改性活產品需要將凍幹（凍幹）疫苗餅與提供的稀釋劑混合，並且應在混合後一小時內使用。

化學改變的疫苗含有改良的活生物體，這些生物體已經在含有調整水平的某些化學物質的培養基中生長，這些化學物質會導致微生物的特定突變。

Modified live vaccines contain whole pathogens that have been altered (attenuated) such that they can't cause clinical disease but can still infect and multiply within the animal. The animal's immune system recognizes the presence of the replicating pathogen to yield an enhanced immune response, negating the need for adjuvants. In general, the immunity produced by modified live vaccines typically lasts longer than the immunity produced by killed vaccines. The major advantage of modified live vaccines is a broader scope and duration of protection because the animal is exposed to all stages of the replicating virus or bacteria. Modified live products require mixing of lyophilized (freeze-dried) vaccine cake with provided diluent and should be used within an hour of mixing.

Chemically altered vaccines contain modified live organisms that have been grown in a media containing adjusted levels of certain chemicals that cause specific mutation of the microorganism.

Temperature sensitive organisms are one example of chemically altered vaccine technology. Temperature sensitive organisms lose the ability to multiply at the animal's normal body temperature but can grow at the temperatures present in eye or nasal mucosa. Thus, if a chemically altered vaccine is given by a route other than direct contact with the mucous membranes, little or no immunity is stimulated. The immune response produced is similar to modified live products, but the duration of immunity is not considered to be as long. The major advantage of chemically altered vaccines is they are safe to use with pregnant animals because there is no systemic replication of the vaccine organism.

Successful vaccination depends on three critical factors: an effective vaccine, a functioning immune system and administration of the vaccine before exposure to the disease. A vaccine may be ineffective if it is mishandled, if a booster is required but not given or because of antigenic differences between the vaccine and field strains of the microorganism to which an animal is exposed.

1.What is a modified live product? 見上
2.Why is time between blending of a MLV and Filling important?

我對疫苗生產沒經驗，純屬猜測，樓主自尋答案。After blending, the MLV is no longer in optimal growth/survival condition anymore, ready to proceed with filling for lyophilization or other long term storage condition.  The extended time could inactivate MLV, reducing the efficacy of vaccination.  Therefore, the shorter the time gap between blending and filling, the better for preserving the MLV activity.