Abstract
Vaccination is among the greatest of all public health and medical advances. It is the most powerful tool that public health has to protect population against infectious diseases. We commonly use the words vaccination and immunization interchangeably, but they have slightly different meanings. Vaccination is the term used for getting a vaccine, either by injection or by taking an oral vaccine. The definition of immunization includes the additional criteria of becoming immune to the disease following vaccination, that is, it requires the body to respond. Interestingly, the World Health Organization (WHO) tends to use the term “immunization” and United Nations Children’s Fund (UNICEF) “vaccination.” Immunization has revolutionized the way that populations and individuals have gained the upper hand against infectious diseases. Vaccines are now being used against some cancers such as cervical carcinoma and liver cancers; this use is set to increase. Vaccines can prevent recurrent chest infections leading to chronic obstructive pulmonary disease (COPD) and bronchiectasis and may soon prevent chronic renal disease and rheumatic heart damage. Perhaps in the future, vaccines may be developed for use against other chronic diseases. Currently, immunization programs prevent 4-5 million deaths per year and could prevent another 1-1.5 million deaths if vaccination was universal.
World Immunization Week is celebrated every year during the last week of April. The WHO, UNICEF, national governments, and non-governmental organizations (NGOs) join together to highlight the actions needed to promote the use of vaccines to protect people of all ages against disease. Its aim is to raise awareness of the global value of vaccines and immunization and promote and support the implementation of high-quality immunization programs. The ultimate goal of World Immunization Week is for more people, and their communities, to be protected from vaccine-preventable diseases. The Expanded Programme on Immunization (EPI) was initiated by WHO and supported by UNICEF in 1974 to advance vaccination toward universal levels.1,2 The original EPI vaccines were diphtheria, tetanus, pertussis, measles, polio, and Bacillus Calmette-Guerin (BCG), and in the decades since, this has expanded to include newer vaccines: Haemophilus influenzae type b, pneumococcal conjugate vaccine, rotavirus series, and human papillomavirus (HPV) vaccines. Newer vaccines including malaria and dengue are being introduced. There are specific vaccines required for travel, including yellow fever, cholera, typhoid, Japanese encephalitis, and rabies. The WHO now provides position papers on vaccines for 27 different diseases. 3 Improving immunization rates directly contributes to Sustainable Development Goal (SDG) 3, to ensure healthy lives and promote well-being for all at all ages through universal health coverage. Immunization is also important if we are to achieve 14 out of the 17 SDGs, such as ending poverty, reducing hunger, and reducing inequalities.
Smallpox was the great success story for vaccination introduced almost 225 years ago. 4 A combination of accurate epidemiology and careful targeting of vaccination led to the elimination of this deadly disease. Unfortunately, there are very few other human pathogens that lend themselves to defeat in this way. Instead, we rely on achieving herd immunity to control the disease. This depends on a high level of population immunity and the dynamics of transmission of the pathogen to prevent the spread of the disease within the community. An estimate of herd immunity of 80% is sometimes used, but for COVID-19 which is highly infectious, it is estimated to be at least 95%. For a disease such as tetanus, the herd immunity must be 100% for everyone to be protected. Vaccines are of varying effectiveness and duration with three doses of pertussis vaccine required to achieve 85% protection in children, but will provide some protection against severe illness in the other 15%. Influenza vaccine is widely used, but the immunity only last 4-6 months, and as the virus mutates frequently, a different formulation is developed each year. Meningococcal ACWY vaccine is very effective, and one dose at 12 months will protect 90% of children.
BCG vaccine, named after two French scientists, Albert Calmette and Camille Guérin, who developed it, is extensively used to prevent tuberculosis (TB). 5 Since its introduction in France a century ago, it has saved millions of lives. BCG also has some effect against leprosy. TB is still one of the world’s greatest killers and BCG has only about 60%-70% efficacy. 6 Now that the technology of mRNA vaccines has been established in developing and producing COVID-19 vaccines, it is to be hoped that in the near future an mRNA vaccine will be developed against TB.
The Global Burden of Disease Network has provided us with detailed estimates of the utilization of 11 commonly used child vaccines.7,8 By 2019, global coverage of third-dose DTP (diphtheria, pertussis, and tetanus) was 81.6% more than double the 39.9% level estimated in 1980. Global coverage of the first-dose measles-containing vaccine (MCV1) increased from 38.5% in 1980 to 83.6% in 2019. Third-dose polio vaccine (Pol3) coverage also increased from 42.6% in 1980 to 79.8% in 2019. Global coverage of newer vaccines increased rapidly between 2000 and 2019, and the number of zero-dose children fell by nearly 75% between 1980 and 2019 from 56.8 million to 14.5 million.7,8 It is estimated that in Asia, 2.1 million children in India and 700 000 in Indonesia were estimated to be unvaccinated or undervaccinated in 2019, prior to COVID-19.
However, during the past decade, global vaccine coverage has plateaued and 94 countries and territories recorded decreasing DTP3 coverage since 2010. Only 11 countries and territories were estimated to have reached a national target of at least 90% coverage for all assessed vaccines in 2019. While final data are not yet available in the past two years, the rates of vaccination in children have fallen even further as the effects of the COVID-19 pandemic have had a universal impact on the delivery of routine vaccination. An estimated 23 million children under the age of one year did not receive basic vaccines, which is the highest number since 2009.
The pandemic has limited travel and the availability of vaccinators. Declining resources have led to a shortage of routine vaccines. When the vaccines are finally given, the increased prevalence of undernutrition could reduce immune responses. 9 It is important to revise routine immunization strategies and programs with an emphasis on equity and underserved populations as the pandemic subsides. Strengthening vaccine data and monitoring systems is crucial to these pursuits, now and through to 2030, to ensure that all children have access to, and can benefit from, lifesaving vaccines.7,8
The control of the COVID-19 pandemic has illustrated the remarkable ability of modern science to develop vaccines against new pathogens very rapidly. A decade of research into the development of mRNA vaccines was quickly applied to remarkably effective and safe COVID vaccines. To date, 10.8 billion doses of COVID-19 vaccines have been administered, an amazing logistic achievement. While there have been 6.6 million deaths reported from COVID-19, without the vaccines the number would have been far greater.
The vaccination effort is also being limited by anti-vaccination, the motivation of which remains a mystery to the hard-working public health community. They promote all kinds of illogical fake news and ignore the benefits that have flowed from vaccination. The movement is not new as shown by James Gilray’s famous cartoon lampooning Edward Jenner’s smallpox inoculation. As the vaccine was developed from cowpox, recipients are shown developing horns and other bovine features. 10 Today, the movement uses social media to publicize its views and had been responsible for thousands, perhaps millions, of unnecessary deaths.
During World Immunization Week, we remember, applaud, and pledge to continue the work of protecting the world through vaccination. This will remain at the core of public health research, teaching, and practice.
The Asia Pacific Academic Consortium for Public Health (APACPH) will be holding its annual conference this year in Manila. The Venue is the College of Public Health at the University of Philippines from September 20 to 23. Details will be available on the APACPH website.