INTRODUCTION:

Vaccination is the administration of antigenic material (a vaccine) to produce immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens. There is strong evidence for the efficacy of many vaccines, such as the influenza vaccine¹, the HPV vaccine² and the chicken pox vaccine³among others. Vaccination is generally considered to be the most effective and cost-effective method of preventing infectious diseases. The material administered can either be live but weakened forms of pathogens (bacteria or viruses), killed or inactivated forms of these pathogens, or purified material such as proteins.

The word vaccination was first used by Edward Jenner in 1796. Louis Pasteur furthered the concept through his pioneering work in microbiology. Vaccination (Latin: vacca—cow) is so named because the first vaccine was derived from a virus affecting cows—the relatively benign cowpox virus-which provides a degree of immunity to smallpox, a contagious and deadly disease. In common speech, 'vaccination' and 'immunization' generally have the same colloquial meaning. This distinguishes it from inoculation which uses unweakened live pathogens, although in common usage either is used to refer to an immunization. The word "vaccination" was originally used specifically to describe the injection of smallpox vaccine.^4-6

Most of the major vaccines used today resulted from the explosive growth of biomedical research after World War II. Enormous advances were made both in biological knowledge, and in the capabilities of research tools including computers and microscopes. For example, in the early 1900s, diphtheria caused more deaths in Australia than any other infectious disease. But, with the introduction of the diphtheria vaccine after World War II, diphtheria has virtually disappeared, the last case being reported in 1993.

The development of efficient vaccines has resulted in a marked decrease in morbidity and mortality from vaccine preventable diseases in Australia and around the world. Most notably, in 1980, smallpox was declared by the world health organisation to have been eradicated. It is hoped that in the future other diseases such as polio and measles will also be eliminated. Today the fight against vaccine preventable diseases continues with huge mass immunisation programs. Australia currently runs a national immunisation program in order to protect our population from this spiteful diseases.⁷

MECHANISM OF ACTION:

In the generic sense, the process of artificial induction of immunity, in an effort to protect against infectious disease, works by 'priming' the immune system with an 'immunogen'. Stimulating immune response, via use of an infectious agent, is known as immunization. Vaccinations involve the administration of one or more immunogens, which can be administered in several forms.

Some vaccines are administered after the patient already has contracted a disease. Vaccine given after exposure to smallpox, within the first three days, is reported to attenuate the disease considerably, and vaccination up to a week after exposure likely offers some protection from disease or may modify the severity of disease.⁸ The first rabies immunization was given by Louis Pasteur to a child after he was bitten by a rabid dog. Subsequently it was found that proper post-exposure prophylaxis (PEP) of potential rabies cases within 14 days infection provides complete protection against the disease.⁹ Other examples include experimental AIDS, cancer and Alzheimer's disease vaccines. The essential empiricism behind such immunizations is that the vaccine triggers an immune response more hastily than the natural infection itself.

Most vaccines are given by hypodermic injection as they are not absorbed reliably through the intestines. Live attenuated polio, some typhoid and some cholera vaccines are given orally in order to produce immunity based in the bowel.¹

TYPES:

All vaccinations work by presenting a foreign antigen to the immune system in order to evoke an immune response, but there are several ways to do this. The four main types that are currently in clinical use are as follows:

Live Vaccines:

Live virus vaccines are prepared from attenuated strains that are almost or completely devoid of pathogenicity but are capable of inducing a protective immune response. They multiply in the human host and provide continuous antigenic stimulation over a period of time, Primary vaccine failures are uncommon and are usually the result of inadequate storage or administration. Another possibility is interference by related viruses as is suspected in the case of oral polio vaccine in developing countries. Several methods have been used to attenuate viruses for vaccine production.

Examples of live attenuated vaccines include:

· Measles vaccine (as found in the MMR vaccine)

· Mumps vaccine (MMR vaccine)

· Rubella (German measles) vaccine ( MMR vaccine)

· Oral polio vaccine (OPV)

· Varicella (chickenpox) vaccine¹⁰

Inactivated whole virus vaccines:

These were the easiest preparations to use. The preparation was simply inactivated. The outer virion coat should be left intact but the replicative function should be destroyed. To be effective, non-replicating virus vaccines must contain much more antigen than live vaccines that are able to replicate in the host. Preparation of killed vaccines may take the route of heat or chemicals. The chemicals used include formaldehyde or beta- propiolactone. The traditional agent for inactivation of the virus is formalin. Excessive treatment can destroy immunogenicity whereas insufficient treatment can leave infectious virus capable of causing disease. Soon after the introduction of inactivated polio vaccine, there was an outbreak of paralytic poliomyelitis in the USA use to the distribution of inadequately inactivated polio vaccine. This incident led to a review of the formalin inactivation procedure and other inactivating agents are now available, such as Beta-propiolactone. Another problem was that SV40 was occasionally found as a contaminant and there were fears of the potential oncogenic nature of the virus.¹¹

Examples of inactivated (killed) vaccines:

· Inactivated polio vaccine (IPV), which is the shot form of the polio vaccine

· Inactivated influenza vaccine¹⁰

Subunit:

Protein subunit – rather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a "whole-agent" vaccine), a fragment of it can create an immune response. Examples include the subunit vaccine against Hepatitis B virus that is composed of only the surface proteins of the virus (previously extracted from the blood serum of chronically infected patients, but now produced by recombination of the viral genes into yeast), the virus-like particle (VLP) vaccine against human papillomavirus (HPV) that is composed of the viral major capsid protein, and the hemagglutinin and neuraminidase subunits of the influenza virus.¹²

Examples include

· Oligomeric: hemoglobin, DNA polymerase, nucleosomes

· Multimeric: ion channels, microtubules

Cytoskeletonproteins:¹³

Recombinant viral proteins:

Virus proteins have been expressed in bacteria, yeast, mammalian cells, and viruses. E. coli cells were first to be used for this purpose but the expressed proteins were not glycosylated, which was a major drawback since many of the immunogenic proteins of viruses such as the envelope glycoproteins, were glycosylated. Nevertheless, in many instances, it was demonstrated that the non-glycosylated protein backbone was just as immunogenic. Recombinant hepatitis B vaccine is the only recombinant vaccine licensed at present.

An alternative application of recombinant DNA technology is the production of hybrid virus vaccines. The best known example is vaccinia; the DNA sequence coding for the foreign gene is inserted into the plasmid vector along with a vaccinia virus promoter and vaccinia thymidine kinase sequences. The resultant recombination vector is then introduced into cells infected with vaccinia virus to generate a virus that expresses the foreign gene. The recombinant virus vaccine can then multiply in infected cells and produce the antigens of a wide range of viruses. The genes of several viruses can be inserted, so the potential exists for producing polyvalent live vaccines. HBsAg, rabies, HSV and other viruses have been expressed in vaccinia¹¹ (Figure:1).

DNA vaccine:

DNA vaccination is a technique for protecting an organism against disease by injecting it with genetically engineered DNA to produce an immunological response. Nucleic acid vaccines are still experimental, and have been applied to a number of viral, bacterial and parasitic models of disease, as well as to several tumour models. DNA vaccines have a number of advantages over conventional vaccines, including the ability to induce a wider range of immune response types.¹⁴

Toxoid vaccines:

Toxoid vaccines are made by treating toxins (or poisons) produced by germs with heat or chemicals, such as formalin, to destroy their ability to cause illness. Even though toxoids do not cause disease, they stimulate the body to produce protective immunity just like the germs' natural toxins.

Examples of toxoid vaccines:

· Diphtheria toxoid vaccine (may be given alone or as one of the components in the DTP, DTaP, or dT vaccines)

· Tetanus toxoid vaccine (may be given alone or as part of DTP, DTaP, or dT)¹⁰

Component vaccines

Some vaccines are made by using only parts of the viruses or bacteria. These vaccines cannot cause disease, but they can stimulate the body to produce an immune response that protects against infection with the whole germ. Four of the newest vaccines are made this way

Examples of component vaccines:

· Haemophilus influenzae type B (Hib) vaccine

· Hepatitis B (Hep B) vaccine

· Hepatitis A (Hep A) vaccine

· Pneumoccocal conjugate vaccine¹⁰

Valence:

Vaccines may be monovalent (also called univalent) or multivalent (also called polyvalent). A monovalent vaccine is designed to immunize against a single antigen or single microorganism. A multivalent or polyvalent vaccine is designed to immunize against two or more strains of the same microorganism, or against two or more microorganisms. In certain cases a monovalent vaccine may be preferable for rapidly developing a strong immune response.¹⁵

CURRENT USE:

Thus far, few experimental trials have evoked a response sufficiently strong enough to protect against disease, and the usefulness of the technique, while tantalizing, remains to be conclusively proven in human trials. However, in June 2006 positive results were announced for a bird flu DNA vaccine¹⁶ and a veterinary DNA vaccine to protect horses from West Nile virus has been approved,¹⁷ a preliminary study in DNA vaccination against multiple sclerosis was reported as being effective.¹⁸

DEVELOPING IMMUNITY:

The immune system recognizes vaccine agents as foreign, destroys them, and "remembers" them. When the virulent version of an agent comes along the body recognizes the protein coat on the virus, and thus is prepared to respond, by (1) neutralizing the target agent before it can enter cells, and (2) by recognizing and destroying infected cells before that agent can multiply to vast numbers.

When two or more vaccines are mixed together in the same formulation, the two vaccines can interfere. This most frequently occurs with live attenuated vaccines, where one of the vaccine components is more robust than the others and suppresses the growth and immune response to the other components. This phenomenon was first noted in the trivalent Sabin polio vaccine, where the amount of serotype- 2 virus in the vaccine had to be reduced to stop it from interfering with the "take" of the serotype 1 and 2 viruses in the vaccine.¹⁹This phenomenon has also been found to be a problem with the dengue vaccines currently being researched, where the Dengue Virus-3 serotype was found to predominate and suppress the response to DEN-1, -2 and -4 serotypes.²⁰

Vaccines have contributed to the eradication of smallpox, one of the most contagious and deadly diseases known to man. Other diseases such as rubella, polio, measles, mumps, chickenpox, and typhoid are nowhere near as common as they were a hundred years ago. As long as the vast majority of people are vaccinated, it is much more difficult for an outbreak of disease to occur, let alone spread. This effect is called herd immunity. Polio, which is transmitted only between humans, is targeted by an extensive eradication campaign that has seen endemic polio restricted to only parts of four countries (Afghanistan, India, Nigeria and Pakistan). The difficulty of reaching all children as well as cultural misunderstandings, however, has caused the anticipated eradication date to be missed several times.¹²

VACCINATION SCHEDULE IN INDIA:

Immunization forms one of the most important and cost effective strategies for the prevention of childhood sicknesses and disabilities and is thus a basic need for all children. The following schedule has been recommended by the Ministry of Health, Govt. of India and is one of the most widely followed by the child health care providers are shown in Table:1.

Table: 1 NATIONAL IMMUNIZATION SCHEDULE

BENEFICIARY	AGE	VACCINE
Infants	Birth	BCG* and OPV**
	6 weeks	DPT and OPV
	10weeks	DPT and OPV
	14 weeks	DPT and OPV
	9 months	Measles vaccine
	18 months	DPT and OPV(Booster dose)
Children	5 years	DT vaccine
	10years	Tetanus toxoid
	16years	Tetanus toxoid

*At birth or at the time of DPT/OPV

** dose called as Zero dose and can be given till 14 days of age, if missed early.

ABBREVIATIONS: BCG: Bacillus calmittee Guerin

DPT: Diphtheria, Pertussis and Tetanus, OPV: Oral Polio Vaccine,

DT: Diptheria and Tetanus vaccine.

THE INDIAN ACADEMY OF PEDIATRICS:

The leading professional organization of pediatricians in our country fully endorses and supports the national schedule. It supplements the above schedule further, with 2 additional vaccines namely Hepatitis B vaccine to be given in three doses (at birth, one month and six months of age). The IAP also recommends MMR (Measles, Mumps and Rubella vaccine) at about 15 to 18 months of age. It must be remembered that even though rubella may appear to be a mild illness, it has a serious potential to cause congenital defects in a baby, whose mother is not protected against rubella and catches the infection during early pregnancy.

The assessment to use the newer vaccines such as Hepatitis A vaccine (Water borne jaundice), Hem.B vaccine and Varicella (chicken pox) vaccine can vary amongst child practitioners and both the parents and the doctor can discuss their usage for their child, as presently, these vaccines are not included in the routine immunization program of our country. Their rational use should be based upon the cost, child's age, parent's concerns, exposure risks to the child and the doctor - parent decision.²¹

ECONOMIC DEVELOPMENT:

Policy makers often consider economic evaluations in deciding whether to introduce a vaccine Into national vaccination schedules or to implement campaigns to improve vaccination coverage (Fuguitt and Wilcox, 1999). Past economic evaluations of vaccinations, however, have usually ignored both important benefits and potentially large cost reductions and may thus have substantially underestimated the value of vaccinations. We demonstrate, for the example of the Hib vaccine, that BCAs have taken narrow evaluation perspectives, focusing on health gains, health care cost savings, and care‐related productivity gains, while ignoring other benefits, in particular, outcome‐related productivity gains (HIB vaccine can prevent permanent mental and physical disabilities), behavior‐related productivity gains (reductions in child mortality due to Hib can trigger changes in fertility which in turn may stimulate economic growth), and community externalities (Hib vaccination can prevent the development of antibiotic resistance and reduce the risk of Hib infection in unvaccinated persons).

It is important to keep in mind that the different benefits and costs included in broadperspective economic evaluations of vaccinations accrue at different times relative to the date of vaccination. For instance, the timing of health gains will depend on the disease avoided by the vaccination – some diseases, such as measles, will mostly affect children, while others, such as hepatitis B, may afflict both children and adults and thus lead to health gains throughout the life course. Outcome‐related productivity gains will usually start accruing only once the vaccinated children have become adults and enter the labor market. Behavior‐related productivity gains may materialize only after a long lag times because changes in child health and survival may first need to be observed in children already born before they can change future fertility decisions. Cost reductions due to changes in vaccine formulation, on the other hand, will be realized immediately at the time of the vaccination. Because the broad perspective evaluation expands the sets of benefits and costs included in the analysis, the relative timing of benefit and cost realization will more complex than in narrow‐perspective studies. Broader evaluation perspectives may thus require more complex evaluation methodologies. The increased demand on the skill of the evaluator, however, should not distract from the fact that broad‐perspective evaluations will improve the validity of evaluation results and should thus be routinely undertaken.¹²

VACCINE PRODUCTION:

Vaccine invention has several stages. First, the antigen itself is generated. Viruses are grown either on primary cells such as chicken eggs (e.g., for Influenza), or on continuous cell lines such as cultured human cells (e.g., for Hepatitis A). Bacteria are grown in bioreactors (e.g., Haemophilus influenza type B). Alternatively, a recombinant protein derived from the viruses or bacteria can be generated in yeast, bacteria, or cell cultures. After the antigen is generated, it is isolated from the cells used to generate it.

A virus may need to be inactivated, possibly with no further purification required. Recombinant proteins need many operations involving ultrafiltration and column chromatography.

Finally, the vaccine is formulated by adding adjuvant, stabilizers, and preservatives as needed. The adjuvant enhances the immune response of the antigen, stabilizers increase the storage life, and preservatives allow the use of multidose vials. Combination vaccines are harder to develop and produce, because of potential incompatibilities and interactions among the antigens and other ingredients involved figure:1^22,23

EXCIPIENTS:

Beside the active vaccine itself, the following excipients are present in vaccine preparation ^24,25(Table-2).

DELIVERY SYSTEMS:

There are several new delivery systems in development, which will hopefully make vaccines more efficient to deliver. Possible methods include liposomes and ISCOM (Immune Stimulating Complex).²⁶

The latest developments in vaccine delivery technologies have resulted in oral vaccines. A polio vaccine was developed and tested by volunteer vaccinations with no formal training; the results were very positive in that the ease of the vaccines increased dramatically. With an oral vaccine, there is no risk of blood contamination. Oral vaccines are likely to be solid which have proven to be more stable and less likely to freeze; this stability reduces the need for a "cold chain": the resources required to keep vaccines within a restricted temperature range from the manufacturing stage to the point of administration, which, in turn, will decrease costs of vaccines. Finally, a microneedle approach, which is still in stages of development, seems to be the vaccine of the future, the microneedle, which is pointed projections fabricated into arrays that can create vaccine delivery pathways through the skin.²⁷

Some characteristics of ideal vaccine:

· Shows an impeccable safety profile in all populations, including young infants, the elderly and immune compromised subjects (such as HIV–positive subjects)

· Elicits a high level of long-lived efficacy, including in young infants and the elderly

· Requires only a single dose (or at most two doses spaced fairly close together) to confer protection

· Stimulates protection within 2 weeks of administration

· Administrable without a needle and syringe; that is, orally, nasally or transcutaneously or with a needle-free injection device

· Administrable in combination with (in the same formulation) or concomitantly (Co-administered) with other vaccines

· Can be manufactured in large scale and with quality control by relatively uncomplicated and economical processes

· Amenable to production in formulations that are resistant to high and low temperatures and therefore free from strict storage requirements.^28,29,30,31

CONCLUSION:

Contemporary technologies offer rational strategies for the development of new and superior vaccines against diseases of public health importance. Regrettably, non-scientific (including financial and bioethical) impediments pose some of the most niggling barriers to the realization of the full application of these technologies. Some infectious diseases trouble mainly populations of developing countries where there are not reliable markets to ensure convalescence of investments in vaccine development. For vaccines against these diseases, what source will fund basic research and the multiple phases 1, 2 and 3 clinical trials needed over 7–12 years to bring a vaccine to licensure? Similarly, how can the complex ethical challenges are best addressed before clinical trials of vaccines are undertaken in vulnerable target populations in developing countries? The accompanying commentaries discuss these critical aspects of vaccine development. Only if acceptable solutions can be found to the financial and bioethical, as well as the technological, barriers facing vaccine development can the impending ‘golden age of vaccinology’ be appreciate.

REFERENCES:

1. Fiore AE, Bridges CB, Cox N J. Seasonal influenza vaccines. Curr. Top. Microbiol. Immunol. 2009; 333: 43–82.

2. Chang Y, Brewer NT, Rinas AC, Schmitt K, Smith JS. Evaluating the impact of human papillomavirus vaccines. Vaccine. 2009; 27. 32: 4355–4362.

3. Liese gang T J. Varicella zoster virus vaccines: effective, but concerns linger. Can. J. Ophthalmol. 2009: 44. 4; 379–384.

4. Lombard M, Pastoret P P, Moulin A M. A brief history of vaccines and vaccination. Rev. - Off. Int. Epizoot. 2007: 26; 1: 29–48.

5. Behbehani AM. The smallpox story: life and death of an old Disease. Microbiol. Rev. 1983. 47 (4): 455–509.

6. Plett PC. Peter Plett and other discoverers of cowpox vaccination before Edward Jenner (in German). Sudhoffs Arch. 2006: 90 .2; 219–232.

7. http://www.health.vic.gov.au/immunisation/general/history

8. Accine Overview .Smallpox Fact Sheet. Retrieved. 2008-01-02.

9. Rupprecht CE, Briggs D, Brown CM., Use of a reduced (4-dose) vaccine schedule for postexposure prophylaxis to prevent human rabies: recommendations of the advisory committee on immunization practices. MMWR Recomm Rep. 2010. 59. (RR-2): 1–9.

10. Cates Lynn. The Main Types of Vaccines Adapted from: National Network for Immunization Information) and the National Immunization Program of the Centers for Disease Control and Prevention (CDC). 2000.

11. http://virology-online.com/general/types of vaccines.htm

12. http://en.wikipedia.org/wiki/Vaccine).

13. http://en.wikipedia.org/wiki/Protein subunit

14. Robinson HL, Pertmer TM. DNA vaccines for viral infections: basic studies and applications. Adv. Virus Res. 2000. 55: 1–74.

15. Questions and answers on monovalent oral polio vaccine type 1 (mOPV1) Issued jointly by WHO and UNICEF.

16. Barnes, Kirsty (2004-06-07). First positive results for DNA-based flu vaccine. In-Pharma Technologist.

17. PR Newswire. Fort Dodge Animal Health Announces Approval of West Nile Virus DNA Vaccine for Horses. 2005-07-18.

18. Stuve, O., Eagar, T.N., Frohman, E.M., Cravens, P.D. DNA Plasmid Vaccination for Multiple Sclerosis. Archives of Neurology. 2007:64. 10; 1385.

19. Sutter RW, Cochi SL, Melnick JL. Live attenuated polio vaccines. In Plotkin SA, Orenstein WA (eds.). Vaccines. Philadelphia: W. B. Saunders. 1999; 364–408.

20. Kanesa-thasan N, Sun W, Kim-Ahn G., Safety and immunogenicity of attenuated dengue virus vaccines (Aventis Pasteur) in human volunteers. Vaccine. 2001. 19 (23–24): 3179–3188.

21. http://www.indiaparenting.com/childs-healthcare/33_1215/ immunization-schedule-for-children.html#rating.

22. Muzumdar JM, Cline RR.. Vaccine supply, demand, and policy: a primer. J Am Pharm Assoc. 2009: 49 .4; 87–99.

23. Bae K, Choi J, Jang Y, Ahn S, Hur B. 2009. Innovative vaccine production technologies: the evolution and value of vaccine production technologies. Arch Pharm Res. 32: 4; 465–480.

24. Grabenstein J D. Immunologic necessities: Diluents, Adjuvants and Excipients. Hosp.Pharm.1996:31; 1387-1392, 1397-1401.

25. Offit P.A, Jew R.K., Addressing parents concerns: Do vaccines contain harmful preservatives, Adjuvants, Additives, or residual. Pediatrics.2003:112;1394-1401.

26. Morein B, Hu KF, Abusugra I. Current status and potential application of ISCOMs in veterinary medicine. Adv Drug Deliv. Rev. 2004; 56.10; 1367–1382.

27. Giudice EL, Campbell JD. Needle-free vaccine delivery. Adv Drug Deliv Rev. 2006:58 (1); 68–89.

28. Kaech, S.M., Wherry, E.J. and Ahmed, R. Nat. Rev. Immunol. 2002: 2; 251–262.

29. Sprent, J. and Surh, C.D. Annu. Rev. Immunol. 2002:20; 551–579.

30. Esser, M.T. Vaccine. 2003:2; 419–430.

31. Agematsu, K., Hokibara, S., Nagumo, H. and Komiyama, A. Immunol. Today. 2000:21; 204–206.

Received on 01.11.2010 Modified on 20.11.2010

Research J. Pharm. and Tech. 4(3): March 2011; Page 369-374

Excipient	Use	Vaccine
Albumin, egg (Ovalbumin)	Growth medium	Influenza, Rabies
Albumin, Human serum	Component of growth medium, Protein stabilizer	Measles, Mumps, Rabies, Rubella
Aluminium Hydroxide	Adjuvants	Anthrax, Hepatitis A, Hepatitis B
Amphotericin B	Antibacterial	Rabies
Ascorbic acid	Antioxidant	Typhoid oral
Beta –propiolactone	Viral Inactivator	Influenza, Rabies
Dulbecco modified eagle medium	Growth medium	Rotavirus
Ethylenediamine tetraacetic acid sodium	Preservative	Rabies, Varicella
Gelatin	Stabilizer in freeze drying	Hepatitis B, Human Papillomavirus ,Influenza, Rubella
Glycerin	Solvent	Vaccine
Monosodium glutamate	Stabilizer	Influenza, Zoster
Phosphate buffer	Adjust buffer	Hepatitis A, Hepatitis B
Polysorbate- 20	Surfactant	Hepatitis A, Hepatitis B