Immunity and vaccines

In a nutshell

Immunity can be natural or artificial. Artificial immunity is a result of vaccination. Vaccination programmes are successful when they protect a large proportion of the population from disease and cause herd immunity. However, some people are opposed to vaccines due to a variety of ethical issues.

Immunity

Definition

Immunity is the ability of an organism to resist infection. There are two types: passive immunity and active immunity.

Passive immunity

Passive immunity occurs when antibodies are introduced into an individual from an outside source. This means no direct contact with the pathogen or antigen is required for immunity as it is immediate. This type of immunity is not long lasting as no memory cells are produced.

Examples

Anti-venom given to snake-bite victims
Antibodies are passed from the mother to the child through the placenta and through breastfeeding.

Active immunity

Active immunity occurs if an individual's immune system is stimulated to produce antibodies, this required direct contact with the antigen. Active immunity takes time to develop and there are two types: natural and artificial active immunity.

Natural active immunity

This occurs when an individual is infected with a disease under normal circumstances. The body produces antibodies and these can provide long-term protection.

Example

Catching a cold from school or work.

Artificial active immunity

This occurs as a result of vaccination. The vaccination is able to induce an immune response that can provide long-term protection but means the person does not suffer from the consequences of the disease.

Example

The annual flu vaccine protects against the yearly strain of Influenza.

Vaccination

Definition

Vaccination is the introduction of a small amount of an inactive or dead form of a pathogen into the body to protect us from disease.

Vaccinations are usually given to children and vulnerable people, as well as people who are going to travel to countries where there is a risk of a serious disease. Vaccines can be given by injection, orally or as a nasal spray.

Examples

MMR vaccine	Protects against measles, mumps and rubella.
HPV vaccine	Protects against Human papillomavirus.
COVID vaccine	Protects against COVID-19.

How do vaccines work?

As well as containing an inactive or dead form of a pathogen, vaccines also contain chemicals that tell your immune system to respond. Lymphocytes then produce antibodies against the pathogen, but as the pathogen is dead or weakened, we don't actually become ill. This ensures that if we ever get infected with a 'live' version of the pathogen, our immune system has memory and can protect us from the infection immediately.

Biology; The immune system; KS5 Year 12; Immunity and vaccines — A. Time, B. Antibody response

1.	The vaccination stimulates the immune system.
2.	Lymphocytes detect antigens from the dead or inactive pathogen and produce a specific antibody against it. Antibodies bind to the antigen.
3.	Lymphocytes remember the antigen of that specific pathogen.
4.	Infection by the pathogen.
5.	The lymphocyte recognises the antigen and produces many specific antibodies. These antibodies bind the pathogens and cause them to be killed before they can make you really ill.

Features of a successful vaccination programme

Vaccines are used as a prevention for many communicable diseases, however, they are not a treatment.

The success of a vaccination programme depends of a variety of factors:

1.	Enough vaccines must be economically available to vaccinate the most vulnerable.
2.	There must be few side effects.
3.	The vaccine must be easily produced, stored and transported.
4.	The vaccine must be easily administered and there must be enough trained staff to administer it.
5.	It must be possible to vaccinate the majority of the population and achieve herd immunity.

Herd immunity

If a large proportion of the population is immune to a pathogen, the spread of it is reduced and it is difficult for the pathogen to spread to the unvaccinated. This is known as herd immunity. Due to the success of vaccination, the WHO (World Health Organisation) declared that smallpox had been completed eradicated worldwide in 1980.

Biology; The immune system; KS5 Year 12; Immunity and vaccines — A: Unvaccinated but still healthy; B: Vaccinated; C: Unvaccinated and infectious

1.	No one in the population is vaccinated and the spread of infectious diseases is high.
2.	Some of the population is vaccinated, but the infectious disease has still high.
3.	The majority of the population is vaccinated, the spread of the infectious disease is contained. This is known as herd immunity.

Herd immunity is important because it is never possible to vaccinate everyone in a large population. For example, babies and young children can not receive certain vaccines as their immune system is not fully functional. Elderly and immunocompromised people also may not be able to receive vaccines as their immune system is weak.

Eliminating disease

Even if vaccines fulfil all of the criteria of a successful vaccination programme, they still may not completely eradicate disease. This can be due to antigenic variability and waning immunity.

Antigenic variability

Some pathogens, in particular viruses, frequently mutate and change the antigens on their surface. This is known as antigenic variability. This means they are less recognisable to lymphocytes and antibodies will no longer be complementary to the antigen on the pathogen. This is why certain vaccines are regularly updated so the immune system has protection against new strains.

Example

The flu vaccine is updated every year.

Boosters

Whilst some antibodies give lifelong protection, like those produced after a measles vaccine, others do not. This is because after a period of time the antibody levels fall below the threshold needed for immunity. Boosters are administered to increase antibody levels again.

Example

COVID-19 antibody levels are reduced after six months. This is why a booster is administered.

Ethical issues

Despite the widespread scientific evidence and the fact that vaccines have saved millions of lives, some people are opposed to them. This is because they raise ethical issues:

1.	The production of vaccines and vaccine trials often involve animals such as mice. This can be considered as cruel.
2.	Vaccines have side-effects and in extreme circumstances, these can cause long-term harm.
3.	There is questions over who vaccines should be tested on and how this should be decided?
4.	Human volunteers may put themselves at unnecessary risk of contracting the disease if they think they are protected.
5.	Some people may be opposed to vaccines on the grounds of religious circumstances or personal beliefs. So should vaccination be compulsory?