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FA16 Immunization Module’s Updates

Live vs. Inactivated Vaccines

Live (attenuated) vaccines are vaccines that confer immunity through the injection a relatively small amount of live microbe that has been weakened (attenuated) in the lab so that it does not cause illness, though it still maintains the ability to grow and replicate. This ability to replicate and proliferate to greater numbers within the host is necessary in order to stimulate a sufficient response and confer immunity.

An inactivated vaccine consists of a microbe that has been killed by chemicals (esp. formalin), heat, or radiation, and may consist of the entire dead microbe, or antigenic fragments. It is for this reason that inactivated vaccines generate primarily a humoral response, with little to no cell-mediated response.

The US Dept. of Health and Human Services website and the CDC effectively summarize and compare these two basic types of vaccines:

Live-attenuated	Inactivated
Pros: Elicits strong humoral and cell-mediated immunity Often confers lifelong immunity and requires less dosages Easy to produce in the lab for viral vaccines	Pros: Non-proliferative microbe, thus ideal for immunocompromised patients No chance for microbe to revert back to virulent form Easy to store and ship (does not require refrigeration) Less affected by circulating antibodies, and thus can be given in infancy or after receiving antibody-containing blood products
Cons: Controlled growth of microbe required, thus unfavorable (contraindicated) for individuals with compromised immune systems Can generate mild symptoms reminicent of "wild-type" disease Theoretically possible for attenuated microbe to revert back to virulent form (only one instance of this so far that occured with the oral polio vaccine) Difficult to store and ship (requires refrigeration) Difficult to produce in the lab for bacterial vaccines Presence of circulating antibodies (e.g. in infancy or after receiving transfusions) can interfere with microbe proliferation and immunogenic efficacy	Cons: Elicits a weaker immune response than live-attenuated vaccines (limited to humoral response) Requires multiple dosages and boosters

Live-attenuated

Inactivated

Pros:

Elicits strong humoral and cell-mediated immunity
Often confers lifelong immunity and requires less dosages
Easy to produce in the lab for viral vaccines

Pros:

Non-proliferative microbe, thus ideal for immunocompromised patients
No chance for microbe to revert back to virulent form
Easy to store and ship (does not require refrigeration)
Less affected by circulating antibodies, and thus can be given in infancy or after receiving antibody-containing blood products

Cons:

Controlled growth of microbe required, thus unfavorable (contraindicated) for individuals with compromised immune systems
Can generate mild symptoms reminicent of "wild-type" disease
Theoretically possible for attenuated microbe to revert back to virulent form (only one instance of this so far that occured with the oral polio vaccine)
Difficult to store and ship (requires refrigeration)
Difficult to produce in the lab for bacterial vaccines
Presence of circulating antibodies (e.g. in infancy or after receiving transfusions) can interfere with microbe proliferation and immunogenic efficacy

Cons:

Elicits a weaker immune response than live-attenuated vaccines (limited to humoral response)
Requires multiple dosages and boosters

As a general rule, the more similar a vaccine is to the actual infectious form of a microbe, the better the immune system can mount an adaptive immune response. Thus, theoretically, live-attenuated vaccines would be the ideal way to generate strong, lasting immunity against a disease. However, in special circumstances where the drawbacks to live-attenuated vaccines are too high of hurdle for reasons often stemming from accessibility or the physiological limitations of a particular patient, inactivated vaccines are alternatively just as effective.

By Elle Meisner
Views: 205

Putting these comparisons in a chart was very helpful! I think looking at these differences is especially important in the context of vaccinations for certain patient populations (e.g. immunocompromised patients & pregnant or lactating women). I also think that a lot of individuals don't really understand the difference between the two and there is a widespread belief that Inactivated vaccines are the only safe and appropriate vaccines.
- Hannah Frudden

This was very informative! I liked how you clearly distinguished the pros and cons of both types of vaccines. I find it interesting that in live vaccines the attenuated microbe technically has the potential to revert back to its virulent form. However, it's amazing how much vaccines have developed since their infancy. I wonder what is the minimum threshold needed in regards to the amount of microbe in a live vaccine.
- Eden Perez

@Ellie Meisner A lot of good information in a clear/concise format! I didn't realize that an inactivated vaccine would not cause a cell mediated response! Based on our discussions in class, I assume that it would not cause a cell mediated response because of its inability to replicate. Is that correct? Or did you see any other specific reason that it would not?
- Troy Watson