World Immunization Week is celebrated annually in the last week of April to highlight the importance of vaccines and how immunisation helps protect people from vaccine-preventable diseases. This year, the theme for World Immunization Week is 'The Big Catch-Up', and under this, the World Health Organization (WHO) is working with partners to accelerate rapid progress of immunisation in countries to ensure that more people, especially children, are protected from preventable diseases. 


The year 2023 marks a global opportunity to catch-up on lost progress in essential immunisation. The aim is to reach the millions of children who missed out on vaccines, restore essential immunisation coverage to at least 2019 levels, build lasting protection in communities and countries, and strengthen primary healthcare to deliver immunisation. 


Immunisation is one of modern medicine's greatest success stories, and prevents deaths every year in all age groups from diseases like diphtheria, tetanus, pertussis (whooping cough), influenza and measles. According to the WHO, immunisation currently prevented four to five million deaths every year.


History of immunisation and breakthroughs in immunology


The basis for vaccination began in the year 1796, when English doctor Edward Jenner noticed that milkmaids who contracted cowpox were protected from smallpox. Jenner knew about variolation, one of the first methods for controlling smallpox. Named after the variola virus, the causative organism of smallpox, variolation was a process during which people who had never contracted smallpox were exposed to material from smallpox sores called pustules by scratching the material into their arm or inhaling it through the nose.  


Jenner guessed that exposure to cowpox could be used to provide protection against smallpox, and tested his theory on James Phipps, the nine-year-old son of his gardener. Jenner inoculated material from the cowpox sore on the hand of milkmaid Sarah Nelmes into the arm of Phipps, and exposed him several times to the variola virus. Surprisingly, Phipps never developed smallpox. 


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After this, vaccination was gradually accepted, and replaced the practice of variolation. In the 1800s, the virus used to make smallpox vaccines changed from cowpox to vaccinia virus. 


Therefore, the smallpox vaccine was the first vaccine. 


Another breakthrough in immunology was the polio vaccine. People were vaccinated against Polio for the first time in West Germany, in the year 1956. A vaccine developed by US physician and immunologist Jonas Salk was used.


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Diseases against which vaccines are available


Currently, vaccines are available against Covid-19, diphtheria, haemophilus influenzae type b, influenza, malaria, measles, mumps, pneumococcal disease, rabies, rubella, tick-borne encephalitis, typhoid, yellow fever, cholera, dengue, hepatitis, human papillomavirus, Japanese encephalitis, meningococcal meningitis, pertussis, poliomyelitis, rotavirus, tetanus, tuberculosis, and varicella, according to the WHO. 


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Pathogens against which vaccines are in development. Know about pipeline vaccines


The pathogens against which vaccines and/or monoclonal antibodies (artificial antibodies that mimic the activities of antibodies in the immune system) are enterotoxigenic Escherichia coli, Herpes simplex virus, HIV-1 (Human Immunodeficiency Virus), Neisseria gonorrhoeae, Norovirus, Salmonella paratyphi, which causes paratyphoid virus, Schistosoma, blood flukes which cause Schistosomiasis disease, Group A Streptococcus, bacteria which cause diseases of the skin and throat, Group B Streptococcus, which cause pneumonia, urinary tract infections, bloodstream infections, skin infections, and bone, joint and soft-tissue infections, Salmonella serotypes other than typhi, paratyphi A, paratyphi B, and paratyphi B, which cause non-typhoidal Salmonella disease, respiratory syncytial virus, which causes infections of the respiratory tract, and Shigella virus, which causes diarrhoea, abdominal pain and fever.


The vaccines in development are called pipeline vaccines. Other pipeline vaccines include improved formulations against tuberculosis, and improved influenza vaccines.


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The need of the population drives the efforts to develop vaccines. Scientists are currently working on vaccines against high-mortality diseases such as those caused by Ebola and Nipah viruses,” Dr Dipu TS, Associate Professor, Division of Infectious Diseases, Amrita Hospital, Kochi, told ABP Live.


Diseases against which vaccines are not available


The diseases against which vaccines are not available, or are not yet widely adopted include AIDS (Acquired Immunodeficiency Syndrome), Dengue, Zika, Cytomegalovirus disease, Ebola, Malaria, and Chagas disease, among others, experts say. 


Cytomegalovirus can cause hepatitis, and affect the eyes, lungs, liver, oesophagus, stomach, and intestines of people with weakened immune systems. 


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Chagas disease is a potentially life-threatening disease caused by the protozoan parasite Trypanosoma cruzi, and is characterised by swelling, rashes, fever, body aches, headache, nausea, diarrhoea and vomiting


“Viral diseases like HIV/AIDS, Dengue, Zika, CMV (Cytomegalovirus), Ebola and bacterial diseases like Tuberculosis and parasitic diseases like Malaria, Chagas disease are the illnesses against which vaccines are either unavailable or not yet widely adopted,” Dr TS said.


According to experts, the current tuberculosis vaccine called BCG (Bacille Calmette-Guérin) is not completely successful in preventing tuberculosis in adults. Therefore, efforts are underway to develop a more effective tuberculosis vaccine. 


“While there is a tuberculosis vaccine (BCG), it is not completely successful in preventing the disease in adults, and efforts to produce a more effective vaccine are continuing,” Varun Sheth, Co-Founder and CEO of Ketto India, told ABP Live.


He emphasised that it is crucial to remember that vaccination research is always evolving, and new vaccines may become accessible in the future.