Advantages & Disadvantages of Live Vaccinations

Because of the variety of different bacteria and viruses we encounter every day, our immune system, the body’s natural defences, is designed to adapt to a wide range of possible infectious agents. Vaccines manipulate this fact by getting the body to respond to harmless versions of disease causing pathogens, or parts of those pathogens that have been inactivated and rendered completely safe. In this article we look at how a particular class of vaccine, live attenuated vaccines, are used and what the advantages and disadvantages of this particular vaccination technology are.

What are the advantages of live attenuated vaccinations?

A live attenuated vaccine is a method of delivering weakened versions of a disease causing pathogen into the human body, where it can induce the immune system into preparing itself for any future encounters with the real, unadulterated virus.

This approach to vaccination has some considerable benefits, not the least of which is durable immunity against diseases that can withstand the test of time. Live vaccinations can usually immunise a person after a single dose, and regular boosters aren’t needed (as is the case with other types of vaccine). The MMR vaccine is an excellent example of an effective live vaccine that only requires one or two doses to achieve its effects. It is estimated that 90% of the people receiving the MMR injection will become immunised after the first dose, and a second dose is provided by the NHS childhood immunisation programme to account for the remaining 10% of the population.

The immune system is a very complex network of sub-systems activated that are activated by different pathogens, and live vaccines effectively activate all of the various elements of the immune response. This means that a more complete immune response occurs as a result of vaccination, and contributes to the fact that only one or two doses of live vaccination are actually needed to effectively immunise an individual.

Live vaccines achieve this end because they are as close to the live, wild-type virus as we can safely get in a vaccine. The results, as discussed above, are more efficient immunisations and a lessened need for booster injections.

Live, attenuated vaccines can also sometimes be delivered by alternative routes. For example a polio vaccine can be delivered orally, reducing the need for injections which many people might not be comfortable with.

Finally live, attenuated vaccines often result in fewer side effects than some alternative forms of vaccination like antibody vaccines.

What are the disadvantages of attenuated vaccines?

While they are extremely effective, there are some caveats to the use of live, attenuated vaccines that need to be considered when using them. One of the primary concerns for example, is the risk of reversion to a more virulent strain of the virus or bacteria being vaccinated against. While the strains of bacteria and viruses used in developing vaccines are carefully selected for characteristics that make them safe for human use, there is always the chance of a secondary mutation (a chance in the genetic material of the organism in question) which could lead to a transformation into a more contagious and virulent form of the microbe. Fortunately there are steps that can be taken by manufacturers to minimise the risk of reversion.

Live attenuated vaccines can’t be safely given to people who are immunocompromised. Basically this means that these patients have weakened immune systems that struggle to deal with infections that a healthy person would barely register. This change in the immune system can come about as a consequence of disease (HIV damages the immune system) or certain kinds of treatment (like chemo- and radiotherapy for cancer). An immunocompromised person won’t be able to fend off attenuated bacteria and viruses, and would probably suffer serious illness rather than gain immunity.

These vaccines are also not given to women during pregnancies. The female body suffers a weakening of the immune system during the pregnancy because of the various pressures exerted by the developing foetus. Moreover, there is a chance of the vaccine making its way into the unborn child where it could cause serious damage.

Finally live, attenuated vaccines can sometimes pose logistical problems when it comes to transport and delivery. These vaccines are only effective if kept and stored at low temperatures, and it can prove difficult to maintain these conditions when a vaccine is being shipped off to a third world country for example.

As this article shows, there are a number of distinct advantages and disadvantages to the use of live, attenuated vaccines. Ultimately the benefits conferred by the use of this particular class of vaccination is significant enough that health authorities across the world make use of live vaccination to protect the population from a host of different, dangerous illnesses.

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