VACCINES

VACCINES FOR COVID-19

A preparation used to stimulate the body defense system by producing antibodies against a particular disease or diseases prepared from the causative microbes of the disease, or its parts, or its toxin, or its synthetic substitute made to act as an antigen without causing the disease.

Types of Vaccines:-

1. Live Attenuated Vaccines:- These are vaccines that contain attenuated or weakened microorganisms that cause disease.

(e.g.)-Measles, Mumps, and Rubella (MMR)

Chickenpox vaccine, Smallpox vaccine, Rotavirus vaccine, and Yellow fever vaccines.

2. Dead Vaccines:- These vaccines contain fully inactivated, or dead microorganisms. These vaccines actually do not produce immunity as strong as the live vaccines.

(e.g)-Hepatitis-A, Rabies, Flu, and Polio.

3.Recombinant or Conjugate Vaccines:-

These vaccines are also called as subunit or polysaccharide vaccines. Specific pieces or polysaccharide portions of the microbes are used to prepare these vaccines with recombinant technology.

(e.g.)-Hemophilus Influenza type-B vaccine

Hepatitis-B, Whooping Cough, Pneumococcal Disease, Meningococcal Disease, Shingles, and Human Papillomavirus.

4. Toxoid Vaccines:- These vaccines use toxins (the harmful venom) of the germs that produce the disease. But the toxins are neutralized to toxoids by chemical treatments.

(e.g.)-Tetanus Toxoid.,Diphtheria Toxoid.

FUTURE VACCINES-GENETIC VACCINES

 DNA VACCINES:- Easy and inexpensive but produce strong and long term immunity.

mRNA VACCINES:

In these vaccines instead of DNA or RNA, the scientists use mRNA,

which is more novel and beneficial, and cost-effective.

mRNA is a fraction of RNA that can be modeled by using DNA as a template with the help of RNA polymerase.

mRNA after entering into the human cells builds up amino acid sequences to produce antigenic proteins to which the body will produce antibodies. 

Moderna Inc a US company is trying to make this type of vaccine for COVID-19 (mRNA-1273 Vaccine) 

COVID-19-VACCINES

A general estimation in vaccines' expertise is that a fast-tracked vaccine development process could speed a successful candidate to market in approximately at least 12-18 months if the process goes smoothly from conception to market availability.

But the currently highlighted vaccines all still need a sufficient period of maturity to be announced as completed one.

But Russia has announced that its vaccine is ready to be marketed without completing its final trial.

India has announced that its vaccine will be ready by December 2020. None of them has passed the minimum required maturity period of 12-18 months.

True science requires a minimum of three trials to be conducted and completed for a drug or vaccine to be approved for marketing.

Trial one (Safety Trial) should be conducted with a few people (50 to 100) for a few months to check the minimum dosage with required efficacy. 

The second Trial (The Extended and EfficacyTrial) should be conducted with a few volunteers (300-500) for a few months with extended age limits say 20 to 80 years.

Third and final trial (The Safety and Security Trial) 

must be conducted with a large group of volunteers, say 3000 to 5000 with unlimited ages to check the safety and reliability of the dosage that is successfully resulted in the second trial.

The minimum required period of the final trial is 1 to 5 years. 

Oxford University-based Astra Zenica company's ChAdOx1 nCoV or AZD1222 vaccine is almost completed the second trial. They are about to start the final trial for which they have recruited about 3000 volunteers worldwide. They have not announced the final date of delivering the finished product to the market.

It is a recombinant viral vector vaccine licensed to Astra Zenica in April '20 and developed by Oxford University in March '20.

The vaccine used a weakened version of adenovirus that causes the common cold in chimpanzees. The virus is encoded with instructions to make proteins from the novel coronavirus to build up immunity.

China's COVID-19 vaccine is developed by the joint venture of the Institute of Biotechnology and Academy of Military Medical Sciences of China. The vaccine is developed by genetic engineering methods similar to the one designed by Oxford University.

Many of the vaccines developed by various countries are using the laboratory engineering method of adenovirus and novel coronavirus recombinant technology similar to Oxford University.

SOME BASICS OF VACCINE ENGINEERING

A. DEAD VACCINE TECHNOLOGY:-

Fig-1

 Indian Covaxin19 developed by BBIL used this technology of the Dead Vaccine method.

The virus is isolated from an infected asymptomatic person by the National Institute of Virology, Pune, and is inactivated by any one of the following methods:-

1.By Heat

An aliquot 320microliter of the viral extract from an infected human cell is taken in a 1.5ml polypropylene cryotube and incubated at a temperature of 75 deg.C for 45 minutes. (see Fig-1)

2.By UV-Light:

An aliquot portion of 2ml of the viral extract taken in 24 well plates is subjected to ultraviolet irradiation. Each plate is filled with the viral extract 1 cm depth. The UV lamp is placed 3cm above the bottom of the solution. A wavelength of 254nm of UV- C radiation is emitted for 15minutes towards the viral sample. ( Fig-1)

Aldehyde  Methods of Inactivations:-

In this method formaldehyde in two dilutions such as 1:1000 and 1:4000 and heated at 37 deg.C for 24 hrs.

Thus inactivated and isolated whole virus supplied by the Pune based NIV is used to produce the COVAXIN19 by the Hydrabad based Bharath Biotec International Limited (BBIL) with the guidance from the ICMR.

This type of vaccine with a dead organism has an advantage of safety and security but has the disadvantage of producing a very weak and short time immunity.

B. LIVE ATTENUATED VACCINE TECNOLOGY

Fig-2

Live attenuated vaccines are made by decreasing the virulence of the living microbes.

The technology is by injecting the virulent virus to a series of chicken embryonic fibroblasts. (See Fig-2). The virus is allowed to infect repeatedly a series of chick cells. By this, the virus begins to adapt itself to infect chick cells. The more to adapt to chick cells the lesser to adapt to human cells and thus the microbe becomes attenuated.

MERITS:-

1. As the vaccine contains a live virus, the body's immune response is intense and immediate that will persist for life.

2.Ease of administration such as oral and nasal.

3.Induction of mucosal Ig-A and systemic Ig-G antibodies.

4.Induction of innate immune responses.

5.Induction of cytotoxic T-cells.

6. Single-dose is sufficient to produce long-lasting immunity without the need for a booster or adjuvant.

DEMERITS:-

1.Possibility of reversion to virulence by the secondary mutation.

2.Not suitable for those who immunocompromised, aged, and those with chronic disease.

3. As these vaccines need cool storage they cannot be easily stored, transported, and used in places where refrigeration is not easily accessible.

VACCINE BY RECOMBINANT TECHNOLOGY

A safe method of vaccine preparation.

Fig-3

Oxford University's Jenner Laboratories is the premier to make the COVID-19 vaccine by this method.

The method is very simple and clear to bring out a safe vaccine.
The basic theory of this vaccine is conjugating the genome of the COVID19 virus into a harmless adenovirus that is attenuated and disabled not to replicate in the human body.  (see Fig-3)

The novel coronavirus contains 4type of proteins.

1.Envelope-The outer membrane cover

2.Capsid    - The inner cover

3.RNA      - The genetic material 

4. S-Spike Protein-The glycoprotein-The small stings like projections spread all over the outer envelope of the virus that gives the look for the coronavirus. 

The Oxford University in its Jenner Institute of Virology made the vaccine with the technical assistance from its spin-out company Vaccitech.

The vaccine is named as AZD1222. The harmless adenovirus which is capable of infecting chimpanzees to produce the common cold. The virus is isolated and injected into a bird and subjected to various processes and treatments to reduce its replicating power. 

Few S-Proteins from the coronavirus were separated and conjugated with the attenuated ChAdOX1 virus by the recombinant technology in order to give a perfect look like the novel coronavirus to trick the human body to believe it as the real COVID19 virus and to trigger the immune response for that. (see Fig-3)

Two trials have been conducted in the Jenner Institute successfully with the result of the successful production of the required antibodies CD8 and CD4 types of T-cells by the human lymphatic system after one month from the date of inoculations.

The produced immune response is to remain for a longe time. To achieve this theVaccitech company decided to give booster vaccine to the volunteers. The booster vaccine contains (Modified Vacciniavaccine Ankara)

MVA an attenuated smallpox virus to which some S-proteins have been combined that has no replicating and spreading power and is safe.

DNA Vaccines Technology:-

Fig-4A

The concept of DNA vaccine is very simple economic and very easy to formulate.

Any eukaryotic or prokaryotic cell contains two types of DNAs that are chromosome DNA and plasmid DNA. (see Fig-4A)

Plasmid DNAs are used to prepare DNA vaccines as they do not provide with pathogenic and replicating genes.

This DNA is carefully extracted by restriction endonuclease enzyme from the eukaryotic cell.

From the virus to which the vaccine is to be produced the genetic code (the DNA insert) is extracted by the same enzymatic method. (see Ig-4-A)

The DNA-insert thus separated is inserted into the plasmid DNA by using the enzyme DNA-ligase (see Fig-4A)

Fig-4B

The final product is genetically engineered plasmid-DNA. This is the vector that has no pathogenic and replicating capacity. Yet it can produce antigenic proteins inside the human cell.

This can be inserted into the human by many methods.

1. The viral content is precipitated on tiny gold beds. The beds can be inserted by helium blasts.

2.By injection

3.By skin patches

4.By nasal spray. (see Fig-4B)

Merits:-

1. Cost-effective as a few 1 or 2 micrograms of the plasmid is enough to produce a strong immune response.

DNA vaccines encoding several antigens can be delivered to the host in a single dose.

2. Produces a long-lasting immunity response.

3.Temperature stable. Storage and transportations are much easier

4.DNA vaccines are able to induce the expression of antigens that resemble native viral epitopes more closely than conventional vaccines do. Conventional vaccines often alter their protein structures and antigenicity.

5. Plasmid vectors can be constructed and made easily and the coding sequence can be manipulated in many ways.

6. The continuous expression of the viral antigen by genetic vaccines among many APCs may promote a successful therapeutic immune response which we cannot obtain with conventional vaccines.

Demerits:-

1. Immune responses cannot produce against microbes who produce antigens made of polysaccharides instead of proteins.

2.Risks of attacking growth-controlling genes.

3.Possibility of anti-DNA body response.

4.Possibility of tolerance to the antigen produced.

5.Possibility of atypical processing of microbial proteins.