Why childhood immunization schedules matter

Infants are highly vulnerable to infection from the moment they are born. While antibodies passed from their mother during pregnancy and through breast milk give them a layer of protection against harmful germs, this immunity only lasts the first few months of life.

Vaccines play a crucial role in safeguarding your child against harmful germs that could cause serious illness or even be life-threatening. For vaccines to work best, they need to be given before your child is exposed to these germs. That's why most childhood immunizations are planned within the first 12 to 18 months of life.

One of the best ways to keep your child safe is to make sure they get their vaccines on time.

The science behind the schedule

The immunization schedule is a plan that shows when children, adolescents and adults should get their vaccines. It is developed by medical experts who assess how diseases spread, who gets sick most often, and at what ages.

The schedule helps to make sure that everyone gets protection at the safest and most important times.

For more than 60 years, the World Health Organization (WHO) and other global health experts, such as the Strategic Advisory Group of Experts on Immunization (SAGE) and national authorities have intensively studied disease transmission, the safety of vaccines and the way they protect people from disease. This has shaped global guidance on what vaccines people need, when they need them, and how many doses are most effective and meet the highest safety standards.

Based on extensive reviews of scientific information, WHO issues vaccine position papers that explain key facts about each disease, the vaccines available to prevent the disease, including their safety evidence, and WHO's recommendations on the timing of each dose.

Every vaccine is recommended at the time it offers the best protection against serious illness. This can mean one type of vaccine is needed at birth, while another is needed in adolescence. Timing of each dose is based on years of research across the world on how the immune system develops, when a person is most at risk of a disease, and how to keep protection strong.

Vaccine schedules differ by country

While WHO makes global recommendations based on best available evidence from decades of research worldwide, each country may slightly adapt the timing of some vaccines to meet their own needs. This is because every country has its own disease patterns, health needs, and systems.

To create their national immunization schedule, each country will use WHO recommendations and summary tables, as well as advice from their National Immunization Technical Advisory Groups. These groups consider local disease patterns, population demographics, cost and availability, and the ease of delivering the vaccines.

Some vaccines are universally recommended and adopted by all countries, such as the hepatitis B birth dose and a 'combination vaccine' that protects against diphtheria, tetanus and pertussis all in one vaccine, given in three doses. These vaccines, in addition to vaccines against Bacillus Calmette-Guérin (BCG), Haemophilus influenzae type B (Hib), polio, measles, rubella, pneumococcal disease, rotavirus, and human papillomavirus (HPV) are recommended by WHO as part of the Essential Programme on Immunization. Even with universal vaccines, the type of vaccine, the manufacturer, the number of doses, and the timing can all differ from one country to another.

In addition to these universal vaccines, some countries include vaccines in their schedule to protect against diseases that are common locally. For example, if you live in a country where dengue, malaria, or yellow fever are endemic, these vaccines may be recommended for your child.

Since there is no fixed global schedule - only global recommendations provided by WHO - the best way to protect your child is to follow your country's national schedule.

Schedules change with scientific advances

Immunization schedules evolve over time. While they are developed based on decades of comprehensive study, our understanding of diseases and vaccines continues to advance, leading to updated recommendations and improved schedules to offer the best protection.

At the same time, a new vaccine can be added to the schedule after in-depth research on safety, vaccine performance, and optimizing where it would fit in the vaccine schedule. Each vaccine will be tested against placebos or current vaccines and added to the schedule at the most appropriate time to offer strongest protection.

As science continues to advance and new vaccines are introduced, immunization schedules have grown more complicated, and our knowledge more established. Combination vaccines, such as the hexavalent vaccine - which protects against diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis and Hib - make things easier by reducing the number of injections. This approach not only simplifies the process for families but also makes it easier to complete the recommended doses on time, requiring fewer visits to a health clinic and fewer injections.

Like single-antigen vaccines, combination vaccines undergo rigorous testing to confirm safety, effectiveness, and the ability to generate immune responses equivalent to those produced by each individual vaccine.

Why follow the schedule?

The immunization schedule is timed to ensure that a child's immune system is ready to respond effectively, providing protection exactly when they need it. Delaying, spacing out or altering vaccine schedules means that your child could be exposed to dangerous diseases for a longer period.

Spacing out vaccines, beyond what is recommended, also requires more visits to the doctor and increases the likelihood that your child will miss a dose, or can result in vaccines being given out of sequence, which is some cases may reduce vaccine performance.

When immunization schedules are delayed or disrupted, there is a sharp increase in the risk of infection not only for the child, but also for the wider community, depending on the disease. Every missed dose increases the chance of falling sick with a disease that could have been prevented and risks putting others in jeopardy.  

Vaccinate your child on time, every time.