Prevention of communicable diseases is a prime priority in India. Immunization for prevention of some diseases of childhood is a well established practice. The national immunization program in India is known as Universal Immunization Program (UIP). Immunization against diphtheria, tetanus, pertussis, tuberculosis, polio and measles is carried out under UIP in India at present (Table 1.1).
The schedule of immunization under the program is noted below.
VACCINES MEANT FOR ADULTS
Typhoid Vaccine
Salmonellosis causes typhoid and paratyphoid fever in several countries even now including in India. Protective vaccination is recommended to prevent the infection both among travelers and indigenous population.
Types of Vaccines Available
- Vi capsular polysaccharide antigen vaccine (VICPS).
- Acetone inactivated vaccine.
- Ty21a oral vaccine.
Primary Vaccination Schedule
- VICPS: VICPS should be administered in a dose of 0.5 ml (25 mcg) intramuscularly one week before travel to an endemic area. The vaccine is suitable for all persons above two years of age.
- Oral vaccine (Ty21a oral vaccine): Four capsules (enteric coated) should be taken orally every alternate day over one week.This vaccine is not suitable for children under six years of age. Booster dosage - four capsules after five years.
- Inactivated whole cell vaccine: It is not recommended for use as it is not well tolerated.
Availability in India
- Typhoral (Aventis) is available for oral use.
- Vactyph (Zydus) is the parenteral vaccine in (0.5 ml) vial.
Precautionary Measures
Live attenuated vaccine should not be used during an attack of fever or gastrointestinal disorder nor should it be used in immune depressed states. It should be avoided if there is history of local or systemic reaction to a previous vaccination.
Drug Interaction
Oral typhoid vaccine capsules should not be taken within 24 hours of use of antibiotics and proguanil. However, there is no interaction between oral typhoid vaccine and other vaccines.
Cholera Vaccine
Cholera vaccine is useful for a short period of protection of about six months as in refugee camps. It is not recommended for travelers as it cannot prevent transmission of infection.
Two types of cholera vaccines are available:
- Parenteral: Inactivated whole cell vaccine.
- Oral: Live attenuated vaccine.
Schedule for Vaccination
- Parenteral vaccine should be administered in two doses at intervals of one or two weeks. It provides protection for six months only.
- Oral vaccine should be administered as single dose in cold or lukewarm water one hour before food or drink.
Seroconversion after oral vaccination is quick (almost 8 days) and the protective efficacy rate is 82 to 100 percent but the protection lasts for six months only.5
Precautionary Measures
Vaccination should be avoided for children less than two years of age.
It should not be undertaken during an attack of fever, gastrointestinal disease and in immunocompromised individuals and pregnant women. Interval between oral typhoid vaccine (Ty21a) and oral cholera vaccine should be at least eight hours. Use of antibiotics and antimalarials should be avoided for at least seven days.
Varicella Vaccine
This vaccine is meant for adults mainly. The main beneficiaries include health care workers, immunocompromised patients and their contacts, international travelers, students and women of child bearing age.
Lyophilized vaccine containing live “oka” strain of varicella- zoster virus is available as varilix (GSK) and varipox (Zydus Biogen) in India.
Immunization schedule: The vaccine should be administered subcutaneously in two doses (0.5 ml) each at interval of eight weeks. It should be avoided in children below one year of age.
Measles-Mumps-Rubella (MMR) Vaccine
Persons born before 1957 are considered immune to measles. Those born after the above date should receive MMR vaccine. One dose of MMR provides adequate protection against mumps and rubella. It should be avoided in pregnant women and women planning to become pregnant in coming four weeks. A second dose of MMR is recommended for adults who were previously vaccinated with killed measles vaccine. Health care worker, college students and international travelers are the main beneficiaries of MMR vaccination.
Pneumococcal Vaccine
Streptococcus pneumoniae is responsible for causing pneumococcal disease particularly in elderly persons (above 65 years), very young children, and among immunocompromised individuals. Bacterial pneumonia, bacteremia and pneumonic meningitis are the conditions in which patients may become very serious. Prevention of such episodes can be achieved by vaccination at appropriate time (Table 1.2).
Two types of pneumococcal vaccines are available:
- 23- valent pneumococcal polysaccharide vaccine.
- 7- valent pneumococcal conjugate vaccine. Both are inactivated vaccines.
Component
Polysaccharide vaccine contains purified capsular protein from 23 types of Streptococcus pneumoniae. However, children under two years of age show poor response to this vaccine.6
The conjugate vaccine contains polysaccharide antigens from seven common types of Streptococcus pneumoniae conjugated to carrier protein and adsorbed into aluminium phosphate. This vaccine should not be used for children under five years of age.
Japanese Encephalitis Vaccine
Japanese encephalitis is the most common form of encephalitis in South East Asia. Almost all cases are found in children below 10 years of age. There is no specific treatment. Nearly one-third of the patients die but more than half of the survivors are left with severe debilitating neurological sequelae. Hence, prevention of the disease by use of a preventable vaccine is of utmost importance.
Currently three types of vaccines are available (Table 1.3). They are:
- Inactivated mouse brain vaccine
- Inactivated primary hamster kidney cell vaccine
- Live attenuated vaccine (SA-14-14-2).
Prevention Among Travelers
International travelers, students, soldiers and missionaries who have to stay for a month or longer in endemic areas particularly during transmission season should receive the protective vaccination. Even in endemic regions individuals who reside in high-risk zones like farmland, rice field, and interior areas need the vaccine. Laboratory workers working in laboratory dealing JE virus also need protection.
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Besides above noted vaccines, some new vaccines are under development. They are verocell derived inactivated vaccine, genetically engineered vaccine and DNA vaccine.
Tomorrow's Vaccines (Vaccines Under Development)
Malaria Vaccine
Since the malaria parasite has several stages in life cycle like liver stage, blood stage (asexual stage), sporozoite and gametocytes, a vaccine needs to be fully effective against these stages. Several candidate vaccines are now under study for prevention of malaria.
The most important advance in development of malaria vaccine was made when in 1984 a vaccine was produced out of irradiated sporozoites. The genes coding for the circumsporozoite protein of plasmodium falciparum, the major surface antigen of the sporozoites were cloned and sequenced. The vaccine was tried for protection of humans but success was limited.
Liver Stage Antigen
A number of liver stage antigens (LSA) apart from CSP has been developed as vaccine candidate (LSA1, LSA3). The liver stage of the parasite is the only stage where it inhibits cell expressing HLA (human leukocyte antigen) and can therefore come under direct T-cell-mediated attack.
Some work has also been done on the development of a blood-stage vaccine. Mostly the work has been concentrated on Merozoite Surface Antigens (MSP1 and MSP2) and ring- infected erythrocyte surface antigen (RESA). A vaccine developed in Columbia (SPF 66) has been tried extensively but found to be ineffective after trial in South America, Tanzania, Gambia and Thailand.
More than 30 different antigens from different stages of life cycle of the parasite are now proposed as vaccine candidates. Transmission blocking vaccines against the gametocytes are also under development. Plasmodium vivax sporozoite vaccine is also a candidate. The vehicle for vaccine also plays an important role in immunogenicity. Antibody response is augmented if the vaccine is presented in alum or liposome. Future malaria vaccines may be multicomponent and multistage vaccines. In fact the major benefit of the vaccine may be to attenuate infection and prevent death from malaria rather than elimination of the disease.
HIV Vaccine
Investigators are working to develop a protective vaccine. However, some are busy to explore a candidate vaccine as therapeutic agent. The best vaccine should be one which can induce antibodies that can neutralize most of HIV-1 subtypes and induce T-cells to inhibit viral replication.8
Some candidate envelope vaccine constructs are undergoing trial in Thailand and the result is eagerly awaited. Several phase one and two trials are under way in different regions. It may be long time before phase three trials are completed.
Japanese Encephalitis Vaccine Under Development
The following vaccines are under development for prevention of Japanese encephalitis.
- Vero cell derived inactivated vaccine: This vaccine is under development and study in Japan, South Korea, Taiwan and China.
- Genetically Engineered Vaccine (Chimeri Vax): It is a new live attenuated vaccine. It uses a reliable flavivirus- yellow fever 17-D as a live vector for the envelope genes of the S-14 -14 -2 virus. The early clinical trials show a promising future. The available results indicate that a single dose will provide life-long immunity against JE.
- DNA Vaccine: It is designed to immunize against multiple flavivirus. The efficacy and immunogenicity are still to be fully determined.
Besides the vaccines discussed above, few other vaccines are also under study. They include rotavirus vaccine, cytomegalovirus vaccine, gonococcal vaccine, leprosy vaccine and toxoplasma vaccine.
Combination Vaccines
These vaccines contain antigens of multiple strains of some infectious agents causing the same disease. These vaccines can reduce the number of pricks, number of visits and decrease the cost of vaccination. Currently following combinations are available:
Hepatitis A + hepatitis B DPT + Hib
DPT+ Hepatitis B DPT + Killed polio
DPT+ Killed polio + Haemophilus influenza B (Pentavirus)
Efforts are in progress to combine as many more vaccines as possible.
BIBLIOGRAPHY
- Anders RF, Saul A. Malaria vaccines. Parasitol today 2000;16:444–7.
- Challenges. Adolesc Med 2000;11:211–24.
- Clyde DF, Mc Carthy VC, Miller RM. Hornick RB Specificity of protection of man immunized against sporozoite-induced malaria. Am J Med Sci 1973;266:398–401.
- Medicine update: Assoc. Physician. India. Ed BK Sahay 2006 Vol 16.
- Shetty NP, Shetty PS. Epidemiology of disease in tropics In: Cook GC, Zumla A (Eds). Manson's Tropical Diseases. 22nd edn. Saunders Elsevier London 2009.pp.19–34.
- Shlim D, Solomon T. Japanese encephalitis: Vaccines for travelers: exploring the limits of risks. Clin Infect Dis 2002;35:183–8.
- Smith D, Inskip-Paulk E. Adolescent Infectious Disease.
- WHO position paper. Typhoid Vaccines: weekly epidemiological record 2000;75:257–64.