疫苗平台

背景

Vaccines work by activating an individual’s immune system to form antibodies and memory cells in response to a pathogen (disease-causing organism), without the individual having to be infected with that pathogen. This means that if or when that pathogen is encountered in the future, the immune system will be able to respond effectively to fight infection, either minimising the symptoms experienced or preventing disease altogether.

Vaccines can be categorised into types based on the technology that they use to initiate an immune response. This technology is referred to as a ‘vaccine platform’.

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Inactivated vaccines are created by using killed or deactivated pathogens or parts of pathogens that are unable to replicate and cause symptoms of disease. This approach to vaccine manufacturing has been used for decades to produce vaccines such as those for hepatitis A and B, polio and the polysaccharide pneumoccal (Pneumovax 23) vaccine. Nuvaxovid (Novavax) is an example of an inactivated protein-based 新冠肺炎 vaccine which utilises only part of the virus (the spike protein).

A benefit of these vaccines is that they are safe to administer to most people including 孕 或者 breastfeeding women or those with 免疫妥协. However, the immune response induced by this mechanism alone may not be as strong or long-lasting compared with that from vaccines using other platforms. To overcome this challenge, booster doses or an adjuvant (ingredient added to vaccines during their manufacture to promote a stronger immune response and better disease protection) may be required.

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Live-attenuated vaccines contain a whole pathogen that has been weakened (attenuated) in a laboratory making it less capable of replicating and causing disease. Examples of live-attenuated vaccines include the 麻疹, mumps, rubella, 水痘（水痘） 和 rotavirus vaccines.

Live-attenuated vaccines typically induce a strong immune response and provide long-lasting immunity meaning fewer doses are required. The main disadvantage of using this platform is that these vaccines are not recommended for use in people who are immunocompromised due to the theoretical risk of causing vaccine-associated disease or to pregnant women due to the potential harm to the unborn baby. In addition, they take longer and are more difficult to mass produce because the pathogen needs to be grown under enhanced biosafety protocols in specialised laboratories.

Genetic vaccines

Genetic vaccines use one or more of a pathogen’s genes (DNA or mRNA) to invoke an immune response. The COVID-19 vaccines Corminaty (Pfizer) and Spikevax (Moderna) are examples of mRNA vaccines and they contain the genetic code specific to the spike protein portion of the virus.

Genetic vaccines can be produced faster than traditional manufacturing methods as development can begin as soon as the genetic sequence of a pathogen is available. Genetic vaccines are only capable of producing proteins and are unable to modify the host’s (vaccine recipient) own genetic material (DNA or mRNA).

Viral vector vaccines

Non-replicating and replicating viral vector vaccines are types of genetic vaccines. They work by using a modified virus (viral vector), which doesn’t cause disease in humans, to carry a portion of the pathogen’s genetic code into human cells.

In non-replicating viral vector vaccines, the individual’s cells will then produce proteins (antigens) specific to the pathogen to trigger an immune response. The COVID-19 vaccine Vaxzevria (AstraZeneca) is an example of a non-replicating viral vector vaccine.

Replicating viral vector vaccines have a similar mechanism but will also create new viral particles to enter further human cells, allowing a quicker and stronger immune response. Replicating viral vector vaccines best mimic natural infection and hence produce a strong immune response and can be used in lower doses.

While viral vectors are well tolerated and highly immunogenic in most people, pre-existing immunity to the viral vector used may hamper the immune response to the vaccine.

Nanoparticle-based vaccines

Nanoparticle-based vaccines have received increasing interest in recent years due to their good safety profile and high immunogenic potential.

Nanoparticle vaccines are constructed by attaching selected key components of a pathogen (such as the COVID-19 spike protein or viral DNA) to an engineered nanoparticle (nanocarrier). This nanoparticle is commonly an engineered virus-like particle (a molecule that mimics the virus but is not infectious). These nanoparticles are highly stable and less prone to degradation than traditional protein vaccines. Gardasil 9 (human papillomavirus) and Nuvaxovid (Novavax COVID-19) vaccines are examples of this approach.

资源

• Australian Immunisation Handbook: Types of vaccines
• Children’s Hospital of Philadelphia, Vaccine Education Centre: Making vaccines: How are vaccines made
• Frontiers in Immunology: Progress and Pitfalls in the Quest for Effective SARS-CoV-2 (COVID-19) Vaccines