Vaccine development andManufacturing process
This paper explains how vaccines are developed and describes in detail their manufacturing process
Vaccines development: Overview and History
The Greeks had two gods of health: Aesculapius and Hygieia, therapy and prevention, respectively. Medicine in the twentieth century retains those two concepts, and vaccination is a powerful means of prevention (1).
Vaccines provide the immunity that comes from natural infection without the consequences of natural infection (2); help protect people from harmful infections before they come in contact with the disease. Vaccines may also help alleviate the symptoms of the infection caused by the virus (3).
The word vaccination (Latin: vaccinus ¼ cow) originated from the first vaccine developed by E. Jenner, since it was derived from a virus affecting cows (4).
Vaccination as a deliberate attempt to protect humans against disease has a short history when measured against the centuries during which man has sought desperately to rid himself of various plagues and pestilences. Only in the 20th century did the practice flower into the routine vaccination of large populations. Despite its relative youth, since the time of Edward Jenner, vaccination has controlled the following 12 major diseases, at least in parts of the world: smallpox, diphtheria, tetanus, yellow fever, pertussis, Haemophilus influenza type b disease, poliomyelitis, measles, mumps, rubella, typhoid and rabies. In the case of smallpox, the dream of eradication has been fulfilled, because this disease has disappeared from the world. Cases of poliomyelitis have been reduced by 99% thanks to vaccination (5).
The earliest vaccines were relatively crude and consisted of partially purified live attenuated virus (e.g., smallpox, rabies) or inactivated bacteria (e.g., pertussis). Over time, more refined methods were introduced such as chemical treatment of a protein toxin to form a toxoid (e.g., tetanus, diphtheria), development of a purified and inactivated virus (e.g., hepatitis A), development of virus-like particles (e.g., hepatitis B, human papillomavirus), and use of purified polysaccharides (e.g., pneumococcal vaccines). Vaccines can generally be classified as whole organism, purified macromolecules, combined antigens, recombinant vectors, synthetic peptides, or DNA, and have been historically introduced in approximately this order (4).
The first vaccines used whole live virus and human-to-human or animal-to-human transfer, such as Edward Jenner’s cowpox (vaccinia) pus inoculation in 1796, intended to immunize against the more pathogenic smallpox in humans. Production methods then advanced to live attenuated virus vaccines produced in vivo or in ovo. Bacterial vaccines were created by Louis Pasteur in the 1880s, including vaccines for chicken cholera and anthrax using weakened bacterial cultures. It was the first major advance after Jenner’s Variolae Vaccinae. The Bacille Calmette Guerin (BCG) vaccine for tuberculosis (TB) was developed around the same time (4, 5).
The pertussis Correspondence to: B. Buckland whooping cough vaccine, licensed in 1918, was the first whole-cell inactivated bacterial vaccine. It was subsequently combined with diphtheria and tetanus toxoids to make the combination diphtheria, tetanus and whole-cell pertussis vaccine (DTwP) and is increasingly being replaced with an acellular subunit vaccine (DTaP) consisting of individual bacterial proteins. Protein subunit and toxoid vaccines came about in the 1930s with the diphtheria and tetanus vaccines, which consisted of bacterial toxins inactivated with formalin (4).
The first in vitro cultivation of a viral vaccine was polio virus in non-neural human cells by Enders in 1949, followed by Salk’s inactivated polio vaccine in primary monkey kidney cells in 1955. The First live polio vaccine was tested in human in 1950 by Hilary Koprowski. Due to the safety risks associated with whole cell and whole virus vaccines, scientists began to create vaccines based on individual pathogen antigens (4, 5)
Historically, vaccines have been developed using these conventional methods that follow the paradigm of isolating, sometimes inactivating, and injecting the disease-causing pathogen or pathogen component. Modern vaccine development is currently exploiting a wide array of novel technologies to create safer and efficacious vaccines including: viral vectors produced in animal cells, virus-like particles produced in yeast or insect cells, polysaccharide conjugation to carrier proteins, DNA plasmids produced in E. coli, and therapeutic cancer vaccines created by in vitro activation of patient leukocytes (4).
Vaccine development is difficult, complex, highly risky, and costly and includes clinical development, process development and assay development. Vaccine development requires strong management systems and controls, and requisite skill sets among scientists and engineers (6). Pharmaceutical companies must demonstrate the safety and efficacy of a medicinal product or vaccine through the use of clinical trials, before a regulatory authority registers the product (3).
Clinical development involves studies of effects of vaccines on patients for safety, immunogenicity and efficacy through a staged process of Phase I early safety and immunogenicity in small numbers, Phase II safety, dose ranging and immunogenicity in 200 to 400 individuals, sometimes Phase IIB non-licensure proof-of- concept (preliminary demonstration of efficacy in animal models or human trials and finally Phase III safety and efficacy trials at a licensure standard (6). These studies typically take about three to five years to complete and are intended to provide an adequate basis for marketing approval (3).
In the process of vaccine development, clinical trials are needed to:
- Identify the appropriate dose of the vaccine that will trigger a protective immune response.
- Identify the appropriate vaccination schedule. A vaccination schedule is a series of times for administrating vaccine. For some vaccines, there will be a need for booster doses after the initial vaccination and the schedule of such doses will also be established.
- Determine the effectiveness of the vaccine in the intended recipients, e.g. adults, elderly, children.
- Determine the safety of the vaccine.
- Determine the consistency of the vaccine study. Such studies are conducted to determine that there is no variability within the final vaccine formulation that may have an effect on the patient.
- Determine whether this vaccine interacts with other vaccines or medicines.
- Determine if the vaccine is able to provide cross protection against other types of antigens (or strains of viruses) (3).
Process development involves making preparations test vaccine that satisfy regulatory requirements for clinical testing including clinical lots, pre - clinical toxicology testing and analytical assessment, and finally scale-up methods which are known to lead to a consistent manufacturing process at 1/10th or full scale usually in three consecutive lots tested in the clinic for immunogenicity. Assay development involves the definition of specific methods to test the purity of raw materials, stability and potency of the vaccine product and immunologic and other criteria to predict vaccine efficacy. Go/no go decisions must be made at each stage of clinical and process development and be data-driven. Clinical, process and assay development tasks must be closely integrated (6).
The manufacturing process (7)
The vast majority of over one billion doses of vaccines manufactured worldwide each year are given to perfectly healthy individuals. It is this fact that drives the requirements for vaccines to be among the most rigorously designed, monitored and compliant products manufactured today.
Process can be broadly divided into two categories:
1. Bulk manufacturing
Cell culture and/ or fermentation-based manufacturing
This step includes the generation of the pathogen itself (for subsequent inactivation or isolation of a subunit) or generation of a recombinant protein derived from that pathogen. Viruses are grown on cells, either primary cells such as chicken fibroblasts (influenza), or on continuous cell lines such as MRC-5 (Hepatitis A). Bacterial pathogens are grown in bioreactors using medium developed to optimize the yield of the antigen while maintaining its integrity (meningitis). Recombinant proteins can be manufactured in bacteria, yeast, or cell culture.
Separation and Purification.
The Next step is to release the antigen from the substrate and isolate it from the bulk of the environment used in its growth. This can be isolation of free virus from cells, secreted proteins from cells, or cells containing antigen from the spent medium.
The next step is the purification of the antigen. For vaccines that are composed of recombinant proteins this may involve many unit operations of column chromatography and ultrafiltration. For an inactivated viral vaccine, there may simply be inactivation of isolated virus with no further purification.