Difference Between Viral Vector and mRNA Vaccines

Explanation of vaccines

Vaccines are medical products that stimulate the immune system to produce an immune response against a particular pathogen, such as a virus or bacterium. They contain small amounts of weakened, dead or synthetic versions of the pathogen or parts of the pathogen, such as proteins, that can trigger an immune response without causing disease.

The immune response produced by vaccines creates an immune memory of the pathogen, allowing the immune system to quickly recognize and fight the pathogen if the individual is exposed to it in the future. Vaccines are a key tool in preventing the spread of infectious diseases and have greatly reduced the incidence of many deadly diseases.

Types of vaccines

There are several types of vaccines, including:

• Inactivated or killed vaccines: These vaccines contain pathogens that have been killed or inactivated by heat, chemicals, or radiation. They cannot cause disease, but can still stimulate an immune response.
• Live attenuated vaccines: These vaccines contain weakened versions of the live pathogen that are unable to cause disease in healthy individuals, but still stimulate an immune response.
• Subunit, recombinant, or conjugate vaccines: These vaccines contain only specific parts of the pathogen, such as proteins or sugars, that can stimulate an immune response.
• mRNA vaccines: These vaccines use a small piece of genetic material called messenger RNA (mRNA) to instruct cells to produce a protein that is found on the surface of the pathogen, triggering an immune response.
• Viral vector vaccines: These vaccines use a modified virus that can infect cells, but has been engineered to produce a protein from the pathogen, triggering an immune response.
• DNA vaccines: These vaccines use a small piece of DNA that contains genetic instructions for producing a protein from the pathogen, triggering an immune response.

The specific type of vaccine used depends on the pathogen being targeted, as well as other factors such as the age and health status of the individual receiving the vaccine.

Importance of vaccines

Vaccines are important for several reasons:

• They protect individuals from infectious diseases: Vaccines stimulate the immune system to produce an immune response against a specific pathogen, allowing the body to fight off the disease if it is encountered in the future. This helps to protect individuals from getting sick and potentially developing serious complications or even dying from the disease.
• They protect communities: Vaccines also provide community immunity, or herd immunity, which occurs when a high percentage of a population is vaccinated, making it difficult for the disease to spread. This helps protect individuals who cannot be vaccinated, such as those with weakened immune systems, infants, and the elderly.
• They help prevent the spread of disease: By reducing the incidence of disease, vaccines help to prevent the spread of disease within communities and even globally. This is particularly important for diseases that are highly contagious and can quickly spread from person to person.
• They are a cost-effective public health intervention: Vaccines are a cost-effective way to prevent disease and reduce healthcare costs associated with treating vaccine-preventable diseases.

Vaccines are an important tool in preventing the spread of infectious diseases and protecting the health and well-being of individuals and communities.

What are Viral Vector Vaccines?

Viral vector vaccines are a type of vaccine that uses a modified virus to deliver a piece of genetic material from a pathogen, such as a virus or bacterium, into the body to trigger an immune response. The modified virus is called a viral vector, and it is typically a harmless virus that has been engineered to produce a protein from the pathogen that is being targeted by the vaccine.

When the viral vector is injected into the body, it infects cells and delivers the genetic material into the cells, causing them to produce the protein from the pathogen. This triggers an immune response that helps the body to recognize and fight off the pathogen if it is encountered in the future.

Examples of viral vector vaccines include the Johnson & Johnson COVID-19 vaccine, which uses a modified adenovirus vector to deliver genetic material from the SARS-CoV-2 virus, and the Ebola vaccine, which uses a modified vesicular stomatitis virus vector to deliver genetic material from the Ebola virus.

Viral vector vaccines have several advantages, including their ability to elicit a strong and long-lasting immune response, as well as their potential to be used to target a wide range of pathogens.

However, they also have some disadvantages, such as the potential for the viral vector to cause an immune response that could limit the effectiveness of subsequent doses, and the need for specialized storage and handling requirements.

What are mRNA Vaccines?

mRNA vaccines are a type of vaccine that use a small piece of genetic material called messenger RNA (mRNA) to instruct cells in the body to produce a protein from a pathogen, such as a virus or bacterium, that triggers an immune response.

The mRNA in the vaccine is synthesized in a lab and encodes instructions for making a specific protein from the pathogen. When the mRNA vaccine is injected into the body, the mRNA enters cells and instructs them to produce the protein from the pathogen. This triggers an immune response that helps the body to recognize and fight off the pathogen if it is encountered in the future.

Examples of mRNA vaccines include the Pfizer-BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine, which use mRNA to instruct cells to produce the spike protein found on the surface of the SARS-CoV-2 virus.

mRNA vaccines have several advantages, including their ability to be rapidly produced in large quantities and their potential to be easily adapted to target new or emerging pathogens. They also do not contain live virus, so they cannot cause the disease they are designed to prevent.

However, they also have some disadvantages, such as the need for specialized storage and handling requirements due to the instability of the mRNA molecule, and the need for two doses to achieve full effectiveness.

Differences Between Viral Vector and mRNA Vaccines

There are several key differences between viral vector vaccines and mRNA vaccines:

• Mechanism of action: Viral vector vaccines use a modified virus to deliver genetic material into cells to produce a protein from the pathogen, while mRNA vaccines use a piece of synthetic genetic material to instruct cells to produce the protein.
• Genetic material: Viral vector vaccines use DNA as the genetic material, while mRNA vaccines use mRNA as the genetic material.
• Storage and handling: Viral vector vaccines generally require colder temperatures for storage and handling than mRNA vaccines. For example, the Johnson & Johnson COVID-19 vaccine needs to be stored at -20°C, while the Pfizer-BioNTech COVID-19 vaccine needs to be stored at -70°C.
• Dose schedule: Viral vector vaccines typically require only one dose, while mRNA vaccines require two doses for full effectiveness.
• Adverse reactions: The types of adverse reactions associated with viral vector vaccines and mRNA vaccines may differ. For example, the Johnson & Johnson COVID-19 vaccine has been associated with a rare blood clotting disorder, while the Pfizer-BioNTech and Moderna COVID-19 vaccines have been associated with a higher incidence of mild side effects such as headache, fatigue, and muscle pain.
• Effectiveness: The effectiveness of viral vector vaccines and mRNA vaccines may vary depending on the specific vaccine and the pathogen being targeted. For example, the Pfizer-BioNTech and Moderna COVID-19 vaccines have shown high efficacy rates in clinical trials, while the Johnson & Johnson COVID-19 vaccine has shown lower efficacy rates.

Both viral vector vaccines and mRNA vaccines have been shown to be effective in preventing infectious diseases, but they differ in their mechanisms of action, genetic material, storage and handling requirements, and adverse reaction profiles.

Conclusion

Vaccines are an essential tool in preventing and controlling infectious diseases. Viral vector vaccines and mRNA vaccines are two types of vaccines that have emerged as promising strategies for preventing a wide range of diseases.

While these two types of vaccines differ in their mechanisms of action, genetic material, storage and handling requirements, and adverse reaction profiles, both have been shown to be effective in triggering an immune response and preventing disease.

The development of safe and effective vaccines is critical to protecting public health and saving lives, and ongoing research and innovation in this area are essential to tackling emerging and re-emerging infectious diseases in the future.

References website

1. Polack FP, Thomas SJ, Kitchin N, et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. N Engl J Med. 2020;383(27):2603-2615.
2. Baden LR, El Sahly HM, Essink B, et al. Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine. N Engl J Med. 2021;384(5):403-416.
3. Voysey M, Clemens SAC, Madhi SA, et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomized controlled trials in Brazil, South Africa, and the UK. Lancet. 2021;397(10269):99-111.
4. Jackson LA, Anderson EJ, Rouphael NG, et al. An mRNA Vaccine against SARS-CoV-2 – Preliminary Report. N Engl J Med. 2020;383(20):1920-1931.
5. Coughlan L, Alberer M, Greinacher A, et al. Adenovirus-associated vaccine-induced thrombosis: Implications for the COVID-19 pandemic. Blood. 2021;137(23):3130-3140.
6. Callaway E. What the data say about AstraZeneca’s COVID vaccine and blood clots. Nature. 2021;592(7854):495-496.
7. World Health Organization. mRNA vaccines against COVID-19. Accessed on March 18, 2023. Available at: https://www.who.int/news-room/questions-and-answers/item/mrna-vaccines-against-covid-19.