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Home » Vaccinate With Confidence » How Vaccines Work: Adverse Effects Following Immunisation (AEFI)

How Vaccines Work: Adverse Effects Following Immunisation (AEFI)

What about Adverse Effects Following Immunisation (AEFI)?

Vaccines are manufactured to meet the most stringent and highest standards of safety. Before vaccines are licensed, the National Regulatory Authorities(NRA) requires many years of research, clinical trials and testing to ensure safety. This process may take 10-15 years or longer.

However, like any medication, vaccines may cause side effects. Once a vaccine is licensed for use, the NRA continually monitors its Adverse Effects Following Immunisations(AEFI). Any hint of a health problem which may or may not be directly related to a vaccine prompts further investigations by the NRA.

If an AEFI is found to be directly related to a vaccine, the NRA will initiate appropriate action, such as changing of vaccine labels or packaging, distributing safety alerts, inspecting manufacturers’ facilities and records, withdrawing recommendations for the use of the vaccine, or revoking the vaccine’s license. 

Every individual is unique and may react differently to vaccinations. In most cases, vaccines are effective in protecting the person from disease and cause no side effects.

A few may experience mild AEFI eg soreness, swelling or redness at the injection site, low grade fever or slight malaise. In extremely rare circumstances, people may experience more serious side effects, like allergic reactions. These reactions are so rare that the risk is very difficult to quantify.

If your child develops a reaction to a vaccine, immediately call your doctor. If the reaction is severe, take your child to your doctor or emergency department immediately. Tell the attending doctor what happened, when it happened, and when the vaccination was given.

“Every individual is unique and may react differently to vaccinations. In most cases, vaccines are effective in protecting the person from disease and cause no side effects.”

In recent years, a number of web sites providing unbalanced, misleading and alarming vaccine safety information were established, raising undue fears among parents and patients. Myths and misinformation about vaccine safety can confuse parents who are trying to make sound decisions about their children’s healthcare. 

Misinformation is rife on the Internet, making it hard to find reliable sources of information. In 2003, the United Nations Children’s Fund (UNICEF), WHO and keys NGOs initiated the Vaccine Safety Net Project (VSN) to respond promptly, efficiently, and scientifically to vaccine safety issues of potential global importance. A list of reliable websites on vaccines in 10 different languages can be found on the website:

“Misinformation is rife on the Internet, making it hard to find reliable sources of information.”

Vaccination is a very common and memorable milestone in a child’s life. As such, all adverse effects are quickly linked to the vaccine as being the cause. While a few sicknesses or reactions that follow vaccination may be caused by the vaccine, many are unrelated events that occur by chance or coincidence.


Risk of AEFI

Hepatitis B

Anaphylaxis: 1 per 1,100,000 doses


Paralysis:1 per 2,500,000 doses of OPV (Oral Polio Vaccine). This risk is not present with Injectable Polio Vaccine (IPV)

BCG (Bacillus Calmette-Guerin), tuberculosis vaccine

· Wound or ulcer at the site of injection that will resolve on its own. It may leave a scar

· Osteomyelitis (bone infection): 5 per 100,000 doses

Diphtheria,Tetanus, and Pertussis (DTaP)

· Seizure:1 per 14,000 doses

· Prolonged crying (3 hours or more): 1 per 1,000 doses

· High fever (40.5 C or more): 1 per 16,000 doses

Haemophilus influenzae type b (Hib)

No significant AEFI

Pneumococcus (PCV, pneumococcal conjugate vaccine)

No significant AEFI


Intussusception (a type of gut obstruction): 1 per 20,000-100,000 doses


· Anaphylaxis: less than 1 per 1,000,000 doses

· Guillain-Barre Syndrome (a disorder of nervous system usually characterized by gradual weakness): 1 per 1,000,000-2,000,000 doses

Measles, Mumps, and Rubella (MMR)

· Anaphylaxis: 1.8-14.4 per 1,000,000 doses

· Febrile seizure: 1 per 3,000-4,000 doses, usually on day 6-14 after immunization, not associated with risk of long term seizure disorder

· Immune thrombocytopenic purpura (a decrease in the number of platelets that play an important role in blood clotting): 1 per 40,000 doses which resolves spontaneously

· Joint aches, between 1-3 weeks after vaccination, resolves spontaneously in 2 days


No significant AEFI

Hepatitis A

No significant AEFI

Varicella (chickenpox)

Mild varicella rash: 1 per 25-50 doses

Human Papilloma Virus (HPV)

Fainting can occur in teenagers after vaccine administration. It is recommended to observe 15 minutes in the clinic after HPV vaccine administration.

Risks by diseases

Hepatitis B

· Chronic hepatitis in 90% of babies born to mothers with active hepatitis B infection

· Cancer of the liver in 40-50% of people with chronic hepatitis


· Chronic hepatitis in 90% of babies born to mothers with active hepatitis B infection

· Cancer of the liver in 40-50% of people with chronic hepatitis


· Meningitis (inflammation of the tissue covering the brain) in 13% of children with TB infecting organs outside the lungs, and 5% in those with TB affecting the entire lungs)


· Airway obstruction with 5-12% risk of deathInflammation of heart (myocarditis)Inflammation of nerves (neuritis)


· Risk of death in 25% of infants with intensive care, much higher without intensive care


· Encephalopathy (disease of brain), Fits, PneumoniaDeath: 2 in 1,000.


· Death:2-5%

Influenzae type b

· Meningitis, Deafness


· Most common cause of meningitis, pneumonia and otitis media in children.

· Risk of death from meningitis is 30% even in developed countries


· Often complicated by secondary bacterial infection

· Risk of death: 1 per 1,000-2,000 cases in developed countries


· Mortality rate: 2-3 per 1,000 cases in developed countries, 10-20 fold in developing countriesRisk of encephalitis (inflammation of the brain): 1 per 1,000 cases in developed countriesRisk of subacute sclerosing panencephalitis (SSPE, a degenerative and fatal neurologic disorder): 4-11 per 100,000 cases


· Deafness, viral encephalitisRisk of orchitis (inflammation of the testis): 17-38%, mayresult in sub-fertility

· May cause miscarriages in girls


· Risk of congenital rubella syndrome (characterised by abnormalities affecting multiple organs) in fetus if a pregnant woman is infected during pregnancy (85% in the first trimester, 25-50% in the second trimester)


· Risk of death: 35% in severe typhoid fever

Hepatitis A

· Hepatitis with risk of liver failureDeath: 1 per 300 cases

Varicella (chickenpox)

· Chickenpox that can be complicated by secondary bacterial infection

Human Papilloma Virus(HPV)

· Risk of cervical cancer, anal cancer, or oral (mouth) cancer with HPV infection

Comparing the two tables enables us to understand that the likelihood of AEFI is generally very small, while the risks from vaccine-preventable diseases are serious and some deadly.

Let us make wise and well-informed decisions for our children with regards to vaccination.

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