Vaccinations are found to work best when most – or ideally, all – of the population have been inoculated against the same infectious disease. This is known as ‘herd immunity’.
This article is the second in a series which will attempt to give a basic overview of vaccines and how they work.
Have you herd? Immunity is in
When a large number of individuals in a community or country are vaccinated, the number of individuals that are likely to be immune to infections is high. This means the risk of an epidemic outbreak is low where most of the population is unlikely to be sick with a particular illness.
In terms of vaccination, herd immunity would be the critical number or threshold level required to reduce cases of infection. This required threshold could differ from one infectious disease to another.
For example, in order to achieve herd immunity for measles, the vaccine coverage in the community must be higher than 90-95%. This means if more than 95% of the population are vaccinated against measles, it is unlikely that a measles outbreak would occur because it would not be able to spread as widely and quickly.
One of the most important things to understand about herd immunity is that in communities with a high vaccination coverage, indirect protection for individuals that cannot be vaccinated can be achieved.
This includes very young children, the elderly and individuals with lower-than-normal immunity, like people receiving treatment for cancer or who have long-term conditions such as kidney disease.
Understanding the concept
With more data and research, scientists have realised that vaccines do not provide perfect immunity. Other factors include different levels of interaction between certain groups.
For example, school-going children are considered to be a high-risk group for the transmission of influenza, or the flu.
In Japan, in the 90s, researchers carrying out a selective influenza vaccination program which targeted school children observed reduced rates of sickness and death among the elderly in the population, a group vulnerable to infection.
This perfectly illustrates the concept of herd immunity in action: when a high-risk group is given sufficient coverage, the disease spreads more slowly or less easily in the rest of the population.
Vaccinations carry certain costs, such as money, time and possible side effects. Because of this, some individuals or groups choose to freeload or not to inoculate because they rely on the indirect protection from the rest of the population.
This has raised heated debates about individual choices versus the needs of a community. While vaccination remains a personal choice, people have been reminded that individual choices have a significant and real impact on community health.
Low herd immunity leads to epidemics
When people or groups choose not to vaccinate due to personal safety concerns or religious beliefs, more outbreaks of vaccine-preventable diseases happen.
In recent years, in the US, measles outbreaks have been linked to particular communities. Just a few months ago, another measles outbreak was reported in the Somali-American community in Minnesota.
This incidence showed how playing on parents’ fears, misunderstandings and lack of knowledge about vaccine safety can have detrimental effects on public health.
It began with an inaccurate report linking rising rates of autism in Somali-American children to the use of the measles, mumps and rubella (MMR) vaccine. This view was encouraged in targeted community outreach programs, by anti-vaccine groups.
This led to a rapid decline in vaccine coverage among children under two years of age in the community, from 92% in 2008, to 42% in recent years. The herd immunity below the level required for protection from the disease consequently and predictably, resulted in a measles outbreak in the state.
Since then, state officials have made attempts to combat the outbreak medically, which is expensive and time-consuming, and to reverse the decade-long beliefs that the vaccine is no longer safe for children.
No jab? No pay and no play
Governments around the world are taking a tougher stance against parents and families who choose not to vaccinate their children.
In Australia, children are required to have their immunisation status updated on the Australian Childhood Immunisation Register. The information here is linked to social security or welfare payments as well as a family’s entitlement to access childcare.
Essentially, if your child has not been fully vaccinated, families receive lower fortnightly payments and their child can be refused access to childcare services. Vaccination objection is not seen as a valid exemption and if an outbreak of a disease occurs, unimmunised children can be excluded from child care for a time.
In Germany this year, the health minister spoke about introducing a law to fine parents up to €2500 for failing to seek advice on vaccination. Kindergartens are expected to report on parents who fail to prove that they have had medical consultations, and can expel children who are not vaccinated. These tougher laws were in response to a measles outbreak earlier in the year, with 410 cases recorded by mid-April.
Italy has also adopted stricter measures. Recently, it was announced that all children had to be vaccinated against 12 common childhood illnesses before enrolment into state-run schools, due to coverage falling below 95% as recommended by WHO. Parents could also be fined if vaccination is not completed by the time their children turn six years old.
Compliance and coverage remain high in Europe, where vaccinations are monitored by the Vaccine European New Integrated Collaboration Effort (VENICE). However, the rise of hesitancy in parents must be addressed to ensure that communities remain protected from future vaccine-preventable outbreaks.
By Najmin Tajudin
A biologist by training, Najmin Tajudin has worked as a management consultant, took the Early Childhood Course in Montessori Theory and Methodology, and ran a community-supported agriculture (CSA) program out of an integrated goat farm. With all 3 kids finally in school, Najmin is looking forward to spending more time on reading books and writing.
If you missed Part 1 of this series, go to What are vaccines and why do we need them?.