These vaccines are prepared by simply inactivating the pathogens. Preparation of killed vaccines may take the route of heat or chemicals. The chemicals used include formaldehyde or beta- propiolactone.
The traditional agent for inactivation of the virus is formalin. Excessive treatment can destroy immunogenicity, whereas insufficient treatment can leave infectious virus capable of causing disease.
Soon after the distribution of inactivated polio vaccine, there was an outbreak of paralytic poliomyelitis in USA due to inadequate processing. This incident led to a review of the inactivation procedure.
Acute Respiratory Distress Syndrome ARDS is a clinical syndrome associated with a variety of pathological findings. These include pneumonia, eosinophilic pneumonia, cryptogenic organizing pneumonia, acute fibrinous organizing pneumonia, and diffuse alveolar damage (DAD). Of these, the pathology most commonly associated with ARDS is DAD.
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Acute Respiratory Distress Syndrome or Acute respiratory disease (ARD) due to adenoviruses caused significant morbidity in military training populations. Since 1971 ARD has been controlled by the use of live, enteric-coated, adenovirus (ADV) types 4 and 7 vaccines.
Potential safety problems with Killed vaccines:
(1) Incomplete inactivation;
2) Increased risk of allergic reactions due to large amounts of antigen involved;
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3) Live vaccines of certain viruses can induce reactivation, or become oncogenic in nature