Vaccines have proven to be a boon to the mankind and can be regarded as potential weapons against infectious diseases. An Ideal Vaccine, like discussed in our previous blog, is the requisite for a disease-free world. And such a vaccine is classified into different types depending on how the antigen(s), the active component(s) that generate a specific immune response against the disease-causing organism, are prepared.
These types broadly include –
- Inactivated vaccines
- Live-attenuated vaccines
- Sub-unit and Nucleic acid-based vaccines
- Toxoid Vaccines
Among these vaccines, Inactivated vaccines were one of the earliest to be developed. Towards the end of the 19th century, the first inactivated vaccines were developed simultaneously by Salmon in the United States and Smith in the Pasteur Institute group in France. A discovery that led to this development is that immunogenicity could be retained if bacteria were carefully inactivated or killed by heat or chemical treatment. However, after successive experiments and strategies by various scientists, 20th century saw the introduction of the first successful inactivated virus vaccine. It was the Influenza vaccine. The second licensed Beta Propiolactone (BPL) – inactivated viral vaccine was a rabies vaccine. In 1950, Inactivated Polio Vaccine was licensed.
Inactivated vaccines are developed by inactivating (killing) the live microorganisms that cause disease through physical or chemical processes. Therefore, this destroys the pathogen’s ability to replicate, but keeps it “intact” so that the immune system can still recognize it and produce an immune response. Till date, several inactivated vaccines have been developed against dreadful diseases like Hepatitis A, Influenza, Polio, Rabies, and they offer excellent protection.
These inactivated vaccines may be administered along with adjuvants to enhance the immune response produced. An adjuvant is an ingredient used in some vaccines that helps create a stronger immune response in people receiving the vaccine. In other words, adjuvants help vaccines work better. Aluminum salts, such as aluminum hydroxide, aluminum phosphate, and aluminum potassium sulfate have been used safely in vaccines for more than 70 years.
Process involved in development of inactivated vaccines:
- Whole viruses or bacteria are extracted and grown in culture.
- Viruses or bacteria are inactivated or killed by chemicals, such as formalin or formaldehyde, and Beta propiolactone (BPL), etc. In some cases, bacteria may instead be inactivated with heat or radiation.
- These inactivated viruses or bacteria are then reproduced in large quantities and prepared for use as a vaccine.
These inactivated viruses or bacteria cannot cause infection but do stimulate immune system, and produce immune responses.
This vaccine approach contains certain benefits – 
- Proven to be extremely safe as they don’t contain any live components.
- Can be given to special populations such as infants, pregnant women and the geriatric population.
They also ensure stability for long-term storage and are technically feasible to produce with fewer regulatory hurdles for licensure. They cater to the requirement of current healthcare environment where focus is on reducing costs while improving overall patient care.