COVID-19 Vaccine Knowlege: What is a subunit vaccine?
COVID-19 Vaccine Knowlege: What is a subunit vaccine? Traditional vaccination methods have actually eradicated several highly infectious diseases worldwide. Despite their success, these conventional methods cannot target many other important pathogens. To overcome these limitations, we have developed a vaccine against several alternative methods, such as subunit vaccines .
The ideal vaccine for any disease should be highly immunogenic, prevent any autoimmune or hypersensitivity reactions, be easy to manage and have simple storage requirements. In addition to these characteristics, the vaccine should also be safe for human or animal administration and not cause disease itself.
In the past few decades, various types of vaccines have been developed to safely induce an individual’s immune response to prevent infection by a variety of different pathogens.
Traditionally, vaccines are composed of complete pathogens that can cause a strong immune response without causing illness in the immunized individual. Three different types of all-pathogen vaccines include inactivated , attenuated live vaccines and chimeric vaccines .
Pathogens are killed by chemicals, heat or radiation before being incorporated into inactivated vaccines, while live attenuated vaccines contain weakened target pathogens. Many whole-pathogen vaccines are widely distributed around the world; however, there are many different pathogens that cannot be effectively targeted to the immune system by this vaccine method.
How to define subunit vaccines and their advantages and disadvantages
In contrast to the whole pathogen vaccine approach, subunit vaccines will only contain certain components derived from pathogenic bacteria, parasites or viruses . These components, also known as antigens , are highly purified proteins or synthetic peptides and are considered to be much safer than the whole pathogen vaccine method.
Another weakness of subunit vaccines is due to possible antigenic denaturation, which may subsequently cause the protein to bind to different antibodies instead of binding to the specific antigen of the targeted pathogen.
What are the adjuvants in subunit vaccines?
Since the antigen alone in the subunit vaccine is not sufficient to produce high immunogenicity, non-immunogenic materials called adjuvants are usually incorporated into vaccine preparations to improve the immune response and enhance the efficacy of the vaccine .
Since the 1930s, the incorporation of trace amounts of aluminum-containing adjuvants (also called alum) into subunit vaccines has been approved. Aluminum adjuvants are one of the most common metals in nature, food and water supplies, and are not easily absorbed by the human body, so they are considered safe when used in vaccines.
With technological advancements in the past few decades, researchers have identified many new promising adjuvant candidates. For example, in 2009, the U.S. Food and Drug Administration (FDA) approved the first vaccine against human papillomavirus (HPV), which contains a new adjuvant AS04, which is the TLR4 agonist 2-O- Deacylated combination-4′-monophosphoryl lipid A (MPL) and aluminum salt combination.
Since then, several natural adjuvants have also been studied for their ability to enhance vaccine immunogenicity without causing toxicity or reactogenicity. In recent years, more and more attention has been paid to the use of natural and synthetic polymers such as chitosan, alginate, hyaluronic acid (HA) and polylactic-glycolic acid (PLGA) as adjuvants for subunit vaccines.
What are the approved subunit vaccines
In the United States, the first subunit vaccine approved for use in humans is the hepatitis B vaccine, which consists of hepatitis B virus surface antigen (HBsAg) derived from the hepatitis B virus. Although the original hepatitis B subunit vaccine obtained HBsAg from the plasma of an infected person, modern recombinant technology has allowed the development of these vaccines without the use of human plasma samples.
By eliminating any potential contamination that may occur when researchers process human plasma, this technological advancement has greatly improved the safety of the hepatitis B vaccine. Targeting acellular pertussis vaccine (acellular Pertussis Vaccine, aP) is another subunit vaccine, pertussis toxin inactivated by the fine and one kind or more microorganisms of the other ingredients.
Future development direction of subunit vaccine
Subunit vaccines have excellent safety; however, researchers interested in the development of new subunit vaccines often face difficulties in identifying suitable antigens or proteins, which can provide the host with good immunogenicity and protection efficiency .
In addition to identifying effective antigens that can be incorporated into future subunit vaccines, it is also important for researchers to develop effective immunostimulatory adjuvants that can be used to enhance the effectiveness of these vaccine types.
The subunit vaccine is considered to be a promising candidate for developing immunity against malaria, tetanus, human cytomegalovirus, Salmonella enteritidis serotype Salmonella enteritidis infection, and even new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) By.