Life Attenuated Vaccines: An Effective Way to Build Immunity Against Many Diseases
What are Life Attenuated Vaccines?
Life attenuated vaccines contain live, weakened (or attenuated) versions of viruses or bacteria that cause disease. These weakened pathogens are able to infect cells and trigger an immune response which develops immunity against the disease, but they do not cause illness or symptoms of disease.
How are pathogens attenuated?
Pathogens are attenuated through repeated culturing in non-human host cells such as chicken eggs or cell cultures. This process weakens the pathogen by decreasing its ability to cause disease while still allowing it to replicate enough to induce protective immunity. Some methods used for attenuation include: deleting specific genes required for full virulence, adapting pathogens to grow at temperatures outside their normal range and serial passage in non-native host cells. Careful testing ensures attenuated pathogens do not regain virulence.
What diseases can life attenuated vaccines prevent?
Some major diseases prevented through life attenuated vaccines include:
- Measles, Mumps, Rubella (MMR): This combined vaccine contains Live Attenuated Vaccines measles, mumps and rubella viruses. It provides long-lasting protection against all three highly contagious diseases. Common side effects are usually mild.
- Varicella (Chickenpox): The varicella vaccine contains a live attenuated strain of the varicella-zoster virus. It protects against primary infection from chickenpox with typical vaccine reaction of a mild rash in some cases.
- Rotavirus: This oral vaccine contains live, attenuated human rotavirus strains to prevent severe diarrhea caused by rotavirus in infants and young children. Side effects are usually mild like fever or mild diarrhea.
- Yellow Fever: The 17D yellow fever vaccine contains a live attenuated yellow fever virus. It provides lifelong protection against this mosquito-borne viral hemorrhagic fever endemic in tropical areas of South America and Africa.
How do Life Attenuated Vaccines work?
When administered, live attenuated vaccines begin replicating in the body, usually in local lymph nodes. This replication mimics natural infection and triggers both humoral immunity through antibody production and cellular immunity mediated by T-cells. Antibodies provide protection by neutralizing or clearing viruses and bacteria from the blood and tissues if later exposed to the wild-type version. Memory B and T cells are also formed which can mount a rapid protective immune response on re-exposure. This confers durable immunity, often for many years or life-long in some cases, after just one or two doses of live attenuated vaccines.
Benefits of life attenuated vaccines
- Long-lasting immunity: Due to replication in the body, these vaccines induce robust, long-term immunity often lasting decades or a lifetime with just one or few doses. This eliminates the need for frequent boosters.
- Broad cross-protective immunity: In addition to neutralizing antibodies, cell-mediated immunity induces broad, cross-protective immunity against many virus variants or strains. This makes life attenuated vaccines very effective.
- Less incubation period: Since the attenuated pathogen can replicate, it triggers a faster immune response compared to inactivated or subunit vaccines that require 2-4 weeks to achieve full immunity. This provides rapid protection.
- Cost-effective: High immunogenicity means less frequent dosing is required, reducing the total costs of vaccination programs compared to multiple doses of other vaccine types. For resource-limited regions where follow-up for boosters could be challenging, live attenuated vaccines are more convenient and affordable.
- Control of outbreaks: The strong, lifelong immunity these vaccines offer has proven effective at controlling global outbreaks and wiped out naturally occurring diseases like smallpox and are on track to eradicate others like polio and measles.
In life attenuated vaccines deliver robust long-lasting protection against many dangerous infectious diseases with few doses. Their ability to induce strong cellular immunity offers cross-protective immunity even against emerging variants. When widely used, they can achieve population-level immunity critical for controlling outbreaks and ultimately eliminating diseases. Overall, this vaccine platform has been proven highly effective through decades of use in expanding global immunization programs.
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