PAN recommends complete vaccination of every child born in Nigeria and those immigrating into Nigeria. The vaccine schedules are recommended by experts in PAN, in collaboration with others in UNICEF and the WHO.

See the vaccine schedules here>>

HISTORY OF VACCINES

Smallpox was a most feared disease resulting in 20-30% mortality and the disease left survivors scarred for life. As part of efforts to control the disease, inoculation, a practice of injecting some of the pox materials into healthy individuals was practiced as early as 10^th century AD. This practice met with varying success with some getting protected and others contracting the disease and dying. Following observations that milkmaids who caught the cowpox were protected against smallpox, Edward Jenner performed an experiment on James Phipps, inoculating him with cowpox material and then challenging him with smallpox. James Phipps was protected and Edward Jenner was the first to publish his works on vaccination as the practice came to be known in 1796. A hundred years later, Louis Pasteur made the first Rabies vaccine

What are vaccines and how do they work?

To understand how vaccines work we must examine the immune system. Immunity is the ability of the body to recognize and tolerate what is “self” while getting rid of what is “non-self”. The body is equipped with the capacity to resist invasion by materials foreign to the body which are recognized as non-self. Following a first time exposure to foreign materials (antigens) which include microorganisms the cells of the immune system respond by developing antibodies, specific helper, and effector T lymphocytes (including cytokine-producing cells) and killer T cells which will help to get rid of the antigen. This reaction takes time and the organism would have caused disease before the immune system can eventually get rid of the organism.  A few of these immune cells develop a state of immunological memory such that when a similar organism is encountered again they respond with faster production of antibodies that bind with greater avidity and cells that kill faster thus getting rid of the organism before it can cause disease.

A Vaccine is any preparation which when administered is able to stimulate the immune system to produce specific responses that inactivate, destroys, or suppresses a given pathogen (microorganism). Thus vaccination is the administration of a vaccine for the prevention of disease while Immunization is the process of inducing immunity artificially. The two words are used interchangeably because vaccination leads to immunization. Vaccination uses the concept of immunity by introducing materials that will induce immune response without causing disease and when an individual subsequently encounters the organism, he/she is able to mount an effective immune response to get rid of the organism without suffering the disease.

Types of immunization

Active immunization is that which induces in the recipient a degree of immunity similar to that achieved from the natural infection and is able to prevent clinical disease. It involves stimulating the immune system to produce antibodies or cell-mediated immunity against an infectious agent. The immunity is produced by the individual’s immune system and is usually long-lasting.

Passive immunization is the administration of exogenously (outside the body of the recipient) preformed antibodies. The immunity produced by this type of immunization is temporary.

Determinants of immune response

Although vaccination should lead to immunization, this is not always the case. The determinants of immune response include

• Chemical and physical state of the vaccine
• Route/site of administration
• Vaccine dose
• Immunogenicity of the vaccine
• Host factors- age, sex, nutrition, presence of preexisting antibodies, genetics, immune status, pregnancy

Herd Immunity

This is the resistance of a group to invasion and spread of an infectious agent due to the immunity of a large proportion of the group. To achieve this, high immunization coverage is necessary. When there is herd immunity, the unimmunized in the population are protected because the infection is unable to spread as most people are immune. However when the proportion of those immunized is low then an infection can spread readily. Often a target of 80% immunization coverage can achieve herd immunity but for highly infectious agents, herd immunity may require immunization coverage of up to 90-95%.

All information on immuisation is evidence-based and are reviewed intermittently by the PAN sub-committee on immunisation to ensure that they are scientific, accurate, and based on recommendations by WHO, UNICEF, and the NPI.

Vaccination is one of the most cost-effective interventions in public health.  Smallpox a disease that ravaged and decimated populations was eradicated in 1977 by the use of vaccination. Poliomyelitis a disease which resulted in deaths and caused profound disabilities for millions of children was endemic in 125 countries prior to the global eradication initiative in 1988. There are currently only two endemic countries Afghanistan and Pakistan while Nigeria and indeed Africa was only just declared polio-free on August 25^th 2020 having not recorded any case of wild polio in the last 3 years.

At the regional level, the Americas have eliminated congenital rubella. Measles had been eliminated in many developed countries until the recent outbreaks stemming from vaccine hesitancy in their populations. Invasive Haemophilus influenzae type b infections were reduced by 99% following the introduction of a vaccine against the organism in the United States of America.  Vaccines continue to prevent 2-3 million deaths yearly. Vaccines work!

Benefits of immunization

• Immunization is able to prevent 2-3 million deaths globally each year.
• Immunizations prevent disease
• Vaccines not only prevent epidemics, but they can also be used to stop the spread of an on-going epidemic
• Disability is the hallmark of some diseases such as poliomyelitis. These disabilities are prevented by immunizing children.
• Vaccines help to save scarce economic resources. The billions of dollars used in the Smallpox eradication effort amount is now being saved because the vaccine is no longer being produced and quarantine facilities for Smallpox are no longer necessary.
• Vaccines prevent suffering. The suffering occasioned by vaccine-preventable diseases is averted by being vaccinated.
• Immunization helps to keep children healthy. When children suffer from vaccine-preventable diseases, their health and immunity are compromised. Immunization keeps children healthy so that they are able to grow and develop normally. Healthy children become healthy adults and produce a healthy nation.
• When children are healthy, they are able to benefit maximally from their education
• Antibiotic resistance is a major global challenge. Vaccines can reduce the development of antibiotic resistance by preventing the occurrence of the infection in the first instance thus precluding the need for antibiotics.  When antibiotics are not used resistance does not occur.
• Immunizations contribute to sustainable development by enhancing productivity. Lost man-hours from parents having to look after children suffering from vaccine-preventable diseases are prevented. Economic losses from caring for children suffering from vaccine-preventable diseases or their long term effects are also prevented

Vaccines are made from a variety of similar ingredients, although they differ in individual constituents. They may also contain residual by-products from the production process. Knowing the precise content of each vaccine can be helpful when investigating adverse events following vaccination and for choosing alternative products for persons with allergies to certain components.

Active components: This consists of the antigen; which is a form of the virus, bacteria, or toxin causing disease. The antigen is however modified and can no longer replicate or cause disease but it can elicit an immune response.

Adjuvants: Adjuvants are a highly heterogeneous group of compounds that have the ability to enhance the immune response. How they work is not entirely understood, but it is postulated that they help keep antigens near the site of injection, meaning that the immune cells can easily access them. Adjuvants are added to vaccines to stimulate the production of antibodies against the vaccine antigen to make it more effective and have been used for decades most often in inactivated (killed) vaccines. There are several hundred different types of adjuvants that are being used or studied in vaccine technology. For example, Aluminium hydroxide and Aluminium phosphate, and there is no evidence of any serious side effects from using them except for occasional minor reactions near the injection site. Adjuvants are also used to reduce the amount of the active component of vaccines.

Antibiotics: These are used during the manufacturing process to prevent bacterial contamination of the tissue culture cells in which the viruses are grown. Usually, only trace amounts appear in vaccines. Commonly used antibiotics include Neomycin and Gentamycin. Persons with known sensitivity to these drugs should be observed for possible reactions after vaccination.

Stabilizers: Stabilizers are used to help the vaccine remain stable and effective during storage. Vaccine stability is important, especially where the cold chain is unreliable. Factors affecting stability include acidity or alkalinity of the vaccine (PH). Stabilizing agents include inorganic salts such as MgCl₂ (for OPV), MgSo₄ (for measles), lactose-sorbitol, and sorbitol –gelatin. Monosodium glutamate and glycine are also sometimes used.

Preservatives and trace components: These are added to multidose and single-dose vaccines to prevent bacterial and fungal growth. They include a variety of substances such as Thiomersal (thimerosal), Formaldehyde or phenol derivatives. Thiomersal is ethyl mercury-containing compound that has generated a lot of debate because of its content, however current evidence shows, there is no evidence of neurotoxicity to Thiomersal (even in trace amounts) in vaccines. Formaldehyde is used to inactivate viruses (IPV) and detoxify bacterial toxins such as those used to make diphtheria and tetanus vaccines.  Although it is purposefully removed during production, the small amounts that remain are too small to cause any harm.

Vaccines are made from a variety of similar ingredients, although they differ in individual constituents. They may also contain residual by-products from the production process. Knowing the precise content of each vaccine can be helpful when investigating adverse events following vaccination and for choosing alternative products for persons with allergies to certain components.

Active components: This consists of the antigen; which is a form of the virus, bacteria, or toxin causing disease. The antigen is however modified and can no longer replicate or cause disease but it can elicit an immune response.

Adjuvants: Adjuvants are a highly heterogeneous group of compounds that have the ability to enhance the immune response. How they work is not entirely understood, but it is postulated that they help keep antigens near the site of injection, meaning that the immune cells can easily access them. Adjuvants are added to vaccines to stimulate the production of antibodies against the vaccine antigen to make it more effective and have been used for decades most often in inactivated (killed) vaccines. There are several hundred different types of adjuvants that are being used or studied in vaccine technology. For example, Aluminium hydroxide and Aluminium phosphate, and there is no evidence of any serious side effects from using them except for occasional minor reactions near the injection site. Adjuvants are also used to reduce the amount of the active component of vaccines.

Antibiotics: These are used during the manufacturing process to prevent bacterial contamination of the tissue culture cells in which the viruses are grown. Usually, only trace amounts appear in vaccines. Commonly used antibiotics include Neomycin and Gentamycin. Persons with known sensitivity to these drugs should be observed for possible reactions after vaccination.

Stabilizers: Stabilizers are used to help the vaccine remain stable and effective during storage. Vaccine stability is important, especially where the cold chain is unreliable. Factors affecting stability include acidity or alkalinity of the vaccine (PH). Stabilizing agents include inorganic salts such as MgCl₂ (for OPV), MgSo₄ (for measles), lactose-sorbitol, and sorbitol –gelatin. Monosodium glutamate and glycine are also sometimes used.

Preservatives and trace components: These are added to multidose and single-dose vaccines to prevent bacterial and fungal growth. They include a variety of substances such as Thiomersal (thimerosal), Formaldehyde or phenol derivatives. Thiomersal is ethyl mercury-containing compound that has generated a lot of debate because of its content, however current evidence shows, there is no evidence of neurotoxicity to Thiomersal (even in trace amounts) in vaccines. Formaldehyde is used to inactivate viruses (IPV) and detoxify bacterial toxins such as those used to make diphtheria and tetanus vaccines.  Although it is purposefully removed during production, the small amounts that remain are too small to cause any harm.

Vaccine-preventable diseases are those for which there is a vaccine. These include diseases caused by viruses and those caused by bacteria.

Vaccine-preventable bacterial diseases include tuberculosis, meningococcal disease, pneumonia (due to Streptococcus pneumoniae and Haemophilus influenza type b), pertussis, tetanus, diphtheria, cholera, Typhoid, Lyme disease, tick-borne encephalitis.

Vaccine-preventable viral diseases include Poliomyelitis, Hepatitis B, Hepatitis A, Measles, Yellow fever, Japanese encephalitis, Rabies, Varicella, Diarrhoea due to rotavirus, mumps, rubella, influenza, dengue,  diseases caused by human papillomavirus (cervical cancer, venereal warts)

Although there are many vaccine-preventable diseases, not all of them are recommended in national immunization programmes. Several factors are taken into consideration before vaccines are recommended. These include;

• Epidemiology of the target disease -incidence, age, sex
• Age-specific morbidity and mortality
• Risk of adverse events from the vaccine
• Cost-effectiveness
• Age of recommended health care visits
• Efficacy of the vaccine

Vaccinations are generally recommended at the age;

• When there is a significant risk of disease and complications
• When the protective immunologic response is expected to occur
• Also recommended for special situations e.g. SCA, HIV

Expanded Programme on Immunization

The Expanded Programme on Immunization (EPI) is the World Health Organization’s immunization programme. The programme started in 1974 with the intention of providing vaccines to all the children in the world. It initially addressed six killer diseases in children. These six diseases tuberculosis, diphtheria, pertussis, tetanus, poliomyelitis and measles were responsible for a high proportion of childhood mortality. With the success of the EPI in reducing morbidity and mortality from these diseases over the years, other diseases have been targeted with the addition of pneumococcal conjugate vaccine, hepatitis B, yellow fever and meningococcal vaccines to the schedule.

Most low and middle-income countries subscribe to the EPI schedule and countries are encouraged to add on other vaccines depending on the epidemiology of their diseases. Nigeria also subscribes to the EPI and her immunization programme is called the National Programme on Immunization in which vaccines are provided free to all children.

The vaccine safety net is a WHO-initiated programme aimed at improving the information available to the general public concerning immunisation in children, in terms of content, and context to prevent undue fear about the safety of vaccines.
The VSN is established to provide understandable, evidence-based information on the safety of vaccines for internet users, regardless of their geographic location and language too long ago, some infants were denied vaccines because their parents were misinformed about the intentions behind the immunisation. PAN partners with VSN to provide safe and effective vaccines and information to the general public and medical practitioners.

Despite the proven benefits of immunization, Nigeria still struggles with vaccine-preventable diseases and perennially low immunization coverage. Peculiar challenges have continued to threaten the gains made in the fight against Vaccine-Preventable Diseases. Among these challenges are inadequate funding of health services, religious beliefs and misconceptions regarding vaccines and vaccine safety, and weak access to health services. These factors, singly and in combination, lead to the low immunization coverage in the country.

Health services including immunization services are poorly funded in Nigeria. Significant funding for the country’s vaccination programme comes from external donors. Due to the tenuous funding, many vaccines are not given on demand. In some cases, clients are pooled to a minimum number below which a vial is not opened even though this practice is not in accordance with the National policy. On occasions, vaccines have been reported unavailable to clients due to breaches in the supply system, leading to the postponement of due immunizations. These practices result in missed opportunities.

In the last decade, the Nigerian healthcare landscape has been bedeviled with strikes from health workers; these strikes have had a negative impact on immunization coverage as often clients have been turned away at such periods of strikes which occur rather too often.

Religious and political considerations have also posed challenges to our vaccine programme. In 2003, protests and boycotts followed the introduction of some vaccines in the northern part of Nigeria owing to rumors of population control through such vaccines. This boycott contributed to the persistence of poliomyelitis for many years after. Apart from religion, there have been unfounded misrepresentations about vaccine safety owing to ignorance among the populace. General practice is to refrain from seeking immunization during minor illnesses. In addition, unrelated deaths have been attributed to immunizations thereby reducing confidence in vaccine services.

Another major challenge to immunization is the operations of Boko haram terrorists, bandits, and other forms of insecurity in some parts of the country which has resulted in many children being orphaned or being in internally displaced persons (IDP) camps. Healthcare workers and volunteers providing services to these IDPs are also abducted and sometimes killed. These factors result in a reduction in available healthcare workers, logistic challenges in transportation, and storage of vaccines, and the children are either not vaccinated or are vaccinated late. There is, therefore, an urgent need to curb the insurgencies and insecurity in these parts of the country to improve access to immunization

The current Covid-19 pandemic has not only limited access to immunization services through the lockdowns, but has revived a number of conspiracies regarding vaccine safety. This situation threatens efforts to reduce under-five mortality in Nigeria. The government should, therefore, strive to restore the confidence of the populace in vaccines, as well as provide continuing education of the masses on the proven safety and efficacy of current vaccines. In addition, there should be increased funding of health services to reduce the reliance on foreign support to maintain immunization services in the country.

The presence of a contraindication increases the risk of developing an adverse reaction to a vaccine recipient, in such a case the vaccine should be withheld. Contraindications are rare (and usually temporary) but misperceptions that they occur frequently lead to refusals to take vaccines and poor immunisation coverage.

The only true contraindication to all vaccines is a previous serious allergic reaction (anaphylaxis) to an earlier received vaccine dose or constituent. Non-absolute contraindications include:

• Severe immunocompromised persons: do not give live vaccines.
• Pregnancy: do not give live attenuated vaccines.
• Occurrence of encephalopathy within 7 days of receipt of a pertussis-containing vaccine which cannot be attributed to another identifiable cause: do not give any other dose of a pertussis-containing vaccine.
• Severe Combined Immunodeficiency (SCID) disease and a history of intussusception: do not give rotavirus vaccines.

Other conditions that can increase the risk of adverse reactions, cause diagnostic challenges, or prevent the production of immunity after vaccination are precautions. The risk from precautions is less than those from contraindications. Where there are precautions, the vaccine should be given if the benefits outweigh the risks but should preferably be deferred until the earliest suitable time. Precautions should be taken in the presence of:

• moderate or severe acute illness with or without fever.
• a family or personal history of seizures (for MMRV vaccine).
• a neurologic disorder
• development of Guillain-Barre Syndrome within 6 weeks after receiving a previous tetanus toxoid –containing vaccine dose or influenza vaccine.
• egg allergy (excluding hives) for the influenza vaccine.
• receipt of antibody-containing blood products within 11 months or less for the varicella vaccine.
• receipt of specific antiviral drugs (acyclovir, famciclovir, vacyclovir) 24 hours before vaccination and 14 days after vaccination for varicella and zoster vaccine

Note that BCG or yellow fever should not be given to infants with symptoms of HIV/AIDS. Health workers should also be taught to recognise signs of adverse reactions and report such reactions to their superiors immediately.

1. Vaccine Safety basics. https://vaccine-safety-training.org/vaccine-components.html#:~:text=Vaccines%20include%20a%20variety%20of,products%20from%20the%20production%20process.{Acessed 14^th August 2020}

2. Centers of Disease control and prevention https://www.cdc.gov/vaccines/hcp/index.html{Acessed 14^th August 2020}

3. Public Health: What goes into a vaccine? https://www.publichealth.org/public-awareness/understanding-vaccines/goes-vaccine/{Acessed 14^th August 2020}

1. UNICEF (2020). Immunization- current status and progress. [Online], Available: https://data.unicef.org/topic/child-health/immunization/ [Accessed 18/8/2020]
2. PAN advisory committee on Immunization. Paediatric Association of Nigeria (PAN) recommended routine immunization schedule for Nigerian children. Niger J Paed 2012;39(4):152-158
3. National Primary Health Care Development Agency. Training manual for the introduction of meningococcal A conjugate vaccine(Men A) in routine immunization in Nigeria. June 2019.
4. World Health Organisation. Vaccine safety basics e-learning course. Module 2. 2020 Available online at https://vaccine-safety-training.org/contraindications.html last accessed 17 August, 2020.
5. Centre for Disease Control. Vaccine recommendations and guidelines of the ACIP. 2020. Available online at https://www.cdc.gov/vaccines/hcp/acip-recs/general-recs/contraindications.html last accessed 17 August, 2020.
6. Rubin L, Levin M, Ljungman P, et al. 2013 IDSA clinical practice guideline for vaccination of the immunocompromised host. Clin Infect Dis 2014;58(3):e44-100. DOI: 10.1093/cid/cit684
7. Kroger A, Atkinson W, Pickering L. General immunization practices. In: Plotkin S, Orenstein W, Offit P, eds. Vaccines. 6th ed. China: Elsevier Saunders; 2013:88-111.
8. Addition of history of intussusception as a contraindication for rotavirus vaccination. MMWR Morb Mortal Wkly Rep. 2011;60(41):1427.
9. Marin M, Broder KR, Temte JL, Snider DE, Seward JF. Use of combination measles, mumps, rubella, and varicella vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2010;59(RR-3):1-12.
10. Grohskopf LA, Sokolow LZ, Olsen SJ, et al. Prevention and Control of Seasonal Influenza with Vaccines Recommendations of the Advisory Committee on Immunization Practices — United States, 2016–17 Influenza Season. MMWR Recomm Rep 2016;65(No. RR-5):1-54.
11. McLean HQ, Fiebelkorn AP, Temte JL, Wallace GS. Prevention of measles, rubella, congenital rubella syndrome, and mumps, 2013: summary recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2013;62(RR-4):1-34.
12. Marin M, Guris D, Chaves SS, Schmid S, Seward JF. Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2007;56(RR-4):1-40.
13. Harpaz R, Ortega-Sanchez IR, Seward JF. Prevention of herpes zoster: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2008;57(RR-5):1-30; quiz CE32-34.
14. National Primary Health Care Development Agency, Nigerian Field Guide on surveillance of adverse events following immunization (AEFI) and response. 2018

Prof Ayebo Sadoh

Dr Chukwuma Onuchukwu

Dr Mariya Mukhtar-Yola

Dr Eno Ekop

Dr Francis Iregbu

Dr Patricia Medupin

Dr Adaobi Bisi-Onyemaechi

Dr Peter Teru

Dr Ogechi Maduka

Dr Iretiola Fajolu

Dr Chris Yilgwan

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