The impact and importance of vaccines cannot be overstated.They provide safe, cost -effective and efficient means of preventing illness, disability and death from infectious diseases. Vaccines, along with the availability of improved medical care, living conditions, and sanitation, can help reduce mortality from infectious diseases. The term ‘vaccine’ is derived from the Latin term ‘vacca’ meaning ‘cow’. The first vaccine was produced by Edward Jenner in 1798 for smallpox, derived from cowpox virus. Discovery of many of the earliest vaccines were more of chance events or ‘scientific accidents’. The early years of the 19th century saw widespread but haphazard use of Jenner's vaccine and finally the World Health Organization and others selected smallpox for eradication from the globe in 1956.

The need for vaccines
Safe and effective vaccines, along with the operational expertise and political commitment, have led to great triumphs in public health, including the eradication of smallpox and the near-eradication of poliomyelitis. Infectious diseases remain the second leading cause of death and the leading cause of disability-adjusted life years (DALYs; 1 DALY = one lost year of healthy life) worldwide.

Apart from endemic diseases, an ongoing threat of new and re-emerging diseases (more than 50 since 1980) and widespread emergence of drug resistance cannot be ignored.

Bioterrorism is terrorism using germ warfare, an intentional human release of a naturally-occurring or human-modified toxin or biological agent e.g.: Anthrax, Ricin, Ebola virus. A need for vaccines is automatically created for specific agents that may be potentially used as bioterrorism agents.

Disease burden – global perspectives
According to WHO, the main causes of illness and death in developed countries are cancer and diseases of the respiratory, cardiovascular and nervous systems. In the developing world, communicable diseases are the main problem; principal causes of death are respiratory infections, HIV/AIDS, infections at birth, diarrhoeal disease and tropical diseases such as malaria or other neglected diseases. It is estimated that only 10 per cent of the world’s medical research is devoted to conditions that account for 90 per cent of the global disease burden. This is known as the 10/90 gap. There is thus an urgent need to develop better drugs and vaccines for diseases that are largely confined to developing countries.

Infectious and parasitic diseases—among the world’s leading causes of death—account for about 33 per cent of the disease burden in poor countries, but only 2.5 per cent in rich countries

Neglected diseases
Neglected diseases are so called because they have been largely overlooked in terms of research into developing new drugs. They include:
● African Trypanosomiasis (sleeping sickness), fatal if untreated. Some 48,000 cases were reported in 1999, although ~300,000 people may carry the infection.
● Leishmaniasis—fatal if untreated—is endemic in 88 developing countries. Most of the 500,000 new cases reported each year are from the Indian sub-continent.
● Chagas disease (Central and South America) has affected around 18 million people and kills ~50,000 people each year.
● Filariasis, Dengue and Schistosomiasis.

Barriers to using available vaccines
● Lack of disease burden data
● Need and maintenance of cold chain or poor transportation and storage systems
● Inadequate and poorly motivated healthcare workers
● Budget constraints and lack of political will

Why don’t the needed vaccines exist?
● Inadequate knowledge/data of global disease burden and the cause of death/disease are not correctly identified as priorities for prevention and control
● Pharmaceutical companies may be less inclined to invest in vaccine R&D: 1223 new medicines were licensed worldwide between 1975 and 1997, while only four were for treatment of tropical diseases.
● Research and development for new vaccines is an elaborate process requiring time and financial resources. In India, estimated R&D expenditure in 2003 was $152 million, whereas major global pharmaceutical companies spent $33200 million.
● Vaccine production may not be possible easily due to complexity of the disease or causative agent; an AIDS vaccine is quite far from being a reality due to the complexity of the Human Immunodeficiency Virus.
● Many developing countries cannot afford to finance vaccine research or purchase vaccines.

Strategy for immunization programmes
● Current strategies utilized in the Expanded Programme on Immunization recommended by the WHO include:
● Routine immunization of infants
● Immunization of women of child-bearing age
● Booster doses
● Disease elimination or eradication initiative
● Assessment of vaccine
coverage
● Immunization programmes and improvements in vaccine development or usage should be based on the following:
● Developing countries have thrust areas that need more attention
● Improving coverage, quality and safety of existing vaccines
● Decrease costs of vaccines (local production)
● Develop easy to use vaccines (no cold chain)
● Decrease the number of dosages
● Targeted vaccination may be able to assist in improving large scale immunizations

Conclusion
Inadequate vaccination strategies and the lack of vaccines still remain one of the leading causes of the diseases burden in developing countries. The need for new or improved vaccines developed specifically against disease causing agents that are usually neglected by the developed countries should serve as initiatives to indigenous R&D. However political will and financial stability of pharmaceutical companies can help bridge the gap between vaccination strategies in the developed as well as developing world.

-The author is senior research fellow, Department of Virology, Haffkine Institute, Mumbai