Viral vector vaccines prepare the body to fight off specific diseases. They deliver genetic instructions to human cells, enabling the body to produce a specific protein from the pathogen. This protein, known as an antigen, becomes the target for the immune system, prompting a protective response without causing illness. These vaccines teach the body to recognize and defend against future infections.
Understanding Viral Vector Vaccines
A viral vector vaccine uses a modified, harmless virus as a delivery system for genetic material. This viral vector is engineered so it cannot cause disease; its disease-causing genes are removed or altered. The vector transports genetic instructions, typically DNA, for a specific protein of the target pathogen into the recipient’s cells.
Once inside the body, the viral vector introduces this genetic blueprint. For instance, in COVID-19 vaccines, the vector carries the DNA instructions for the SARS-CoV-2 spike protein. This genetic material does not integrate into a person’s genome, ensuring the vaccine’s safety profile.
How They Trigger Immunity
Immunity begins when the viral vector, carrying its genetic payload, enters human cells. The vector attaches to specific receptors on the cell surface, allowing it to gain entry. Once inside, the viral vector releases the genetic material, which is then transported to the cell’s nucleus or cytoplasm.
The cell’s internal machinery then reads these genetic instructions and produces the target protein, such as a viral spike protein. This protein is then displayed on the surface of the cell. The body’s immune system recognizes this protein as foreign, even though it was produced by its own cells.
This recognition initiates an immune response, involving both B-cells and T-cells. B-cells produce antibodies that bind to the foreign protein, neutralizing it or marking it for destruction. T-cells are activated, including cytotoxic T-cells that identify and eliminate cells displaying the foreign protein. This response creates immunological memory, preparing the body to defend against future encounters with the pathogen.
Common Viral Vectors and Their Applications
Several types of viruses are adapted as vectors for vaccine development due to their well-understood characteristics and safety profiles. Adenoviruses are frequently used, including human adenovirus serotypes like Ad26 and Ad5, and modified chimpanzee adenoviruses such as ChAdOx1. These vectors are chosen for their high efficiency in delivering genetic material and their ability to infect a broad range of cell types.
Other viral vectors include the vaccinia virus, which has a long history in vaccine development, and the vesicular stomatitis virus (VSV). The measles virus and influenza viruses have also been explored as vaccine vectors. These vectors are engineered to be replication-deficient, meaning they can deliver genetic material but cannot replicate and cause illness.
Viral vector vaccines combat various infectious diseases. Examples include COVID-19 vaccines, where adenoviral vectors like Ad26 and ChAdOx1 delivered the SARS-CoV-2 spike protein gene. The rVSV-ZEBOV vaccine, known as Ervebo, is approved for preventing Ebola, using a genetically engineered vesicular stomatitis virus. These different vectors offer versatility in vaccine design, allowing for selection based on factors like pre-existing immunity to the vector in the target population or the desired immune response.
Safety and Regulatory Oversight
Viral vector vaccines undergo extensive and rigorous testing before approval for public use. The development process involves multiple phases of clinical trials to assess safety, dosage, and efficacy. Phase 1 trials focus on safety in a small group of healthy volunteers. Phase 2 expands to a larger group to evaluate dosage and initial effectiveness.
Phase 3 trials involve thousands of participants, designed to confirm efficacy and detect less common side effects. Regulatory bodies worldwide, such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA), review the vast amounts of data generated during these trials. They scrutinize the quality, non-clinical, and clinical aspects of the vaccine to ensure benefits outweigh any potential risks.
Following approval, vaccines are subject to continuous monitoring through pharmacovigilance systems. This ongoing surveillance aims to detect rare or very rare adverse events that might only become apparent with widespread use. Common side effects, such as pain at the injection site, fatigue, headache, or fever, are generally mild to moderate and temporary. Regulatory agencies encourage the timely reporting of any suspected adverse reactions to maintain a comprehensive safety profile and ensure public health.