In 1796, Edward Jenner, who was one of the first English doctors to include planned regular examinations in treatment programmes for his patients, noticed that patients who suffered from cowpox did not appear to get sick from a far more deadly and highly infectious disease – smallpox.
To confirm his observations, and after obtaining permission from the foster parents of a young orphaned boy, Jenner deliberately infected the boy with cowpox by taking liquid from another patient’s actual cowpox sores and scratching some of it into the boy’s skin. Six weeks later, using the same method, he scratched some liquid smallpox venom into the boy.
After almost one month, no symptoms which would indicate smallpox illness occurred. The success of this planned experiment by Jenner became recognised as the first scientific demonstration of injecting a person with one virus to provide protection against other and potentially more dangerous viruses.
In his description of this technique of injecting people with cowpox to provide protection (now termed ‘immunity’) against smallpox, Jenner introduced the word ‘vaccine’ which he composed from the scientific name for cowpox, ‘variola vaccina’; – vaccina meaning ‘of the cow’. The orphan boy concerned was also the first person ever to get a vaccination and it was not until almost a hundred years later that vaccinations started to be used again, starting with protection against cholera in 1879.
Thereafter, vaccines against other diseases were devised and applied more widely and with increasing frequency.
Vaccines now protect against many different diseases, such as: cervical cancer, cholera, diptheria, hepatitis B, influenza, measles, mumps, pneumonia, polio, rabies, tetanus, typhoid, varicella and yellow fever. Many other vaccines are currently under development including those that protect against ebola and malaria. Cervical cancer provides an interesting example of a high success rate – virtually all cervical cancer cases start with a sexually transmitted human papillomavirus (HPV) infection. If given before exposure to the virus, vaccination offers the best protection against the disease. Following vaccination, reductions of 90% or even more in HPV infections in teenage girls and young women have been demonstrated by studies conducted in Australia, Belgium, Germany, New Zealand, Sweden, the United Kingdom and the United States of America.
Vaccines do not act directly against invading organisms, commonly referred to as ‘germs’, but enable natural defences of bodies to recognise invading germs such as viruses or bacteria and also to produce antibodies which are proteins tailored specifically to fight infections.
“Rather than having to treat a disease after it occurs, vaccines prevent sickness in the first place.”
The memory functions induced by vaccines continue to operate, providing protection against diseases for years, decades or even a lifetime. This is what makes vaccines so effective. Rather than having to treat a disease after it occurs, vaccines prevent sickness in the first place. In addition, people who have been vaccinated are less likely to transmit viruses or bacteria to others including those who cannot be vaccinated due to health conditions such as allergies, or advanced age.
Frequently, a desirable objective to achieve by communities and populations is what is termed ‘herd immunity’, the term now commonly used for indirect protection from an infectious disease that happens when immunity develops in a population either through vaccination or through previous infection.
Herd immunity arises when individuals who are not immune are in communities which contain high proportions of those who are immune and is only achieved by person-to-person transmission. Not all infectious diseases can produce herd immunity. For example, tetanus infections come from bacteria in the environment, not from other people.
The WHO supports achieving ‘herd immunity’ through vaccination, not by allowing a disease to spread through a population, as this would result in unnecessary cases and deaths.
To combat Covid-19 causing the relatively new global pandemic, many vaccines are still in development phases although some have now progressed to early treatment rollout, having demonstrated safety and efficacy against the disease.
The proportion of the population that must be vaccinated against Covid-19 to begin inducing herd immunity is not yet known, but is an important area of research and will, no doubt, vary according to the community, the vaccine, the populations prioritised for vaccination, and other factors.
All the ingredients of a vaccine play an important role in ensuring a vaccine is safe and effective. Typical ingredients are:
- Antigens: Killed or weakened forms of viruses or bacteria, which train our bodies to recognise and fight the disease when it occurs
- Adjuvants: Which help boost immune responses so that they help vaccines to work better.
- Preservatives: Which ensure a vaccine stays effective.
- Stabilisers: Which protect vaccines during storage and transportation.
Vaccine ingredients can look unfamiliar when they are listed on a label. However, many of the components used in vaccines occur naturally in the body, in the environment, and in the foods we eat.
All of the ingredients in vaccines – as well as the vaccines themselves – are thoroughly tested and monitored to ensure they are safe.
Vaccines currently need to be maintained at relatively low temperatures ranging between – 15 and – 80°C. Several commentators have pointed out that continually increasing demand for vaccines offers a “key opportunity to create a new global cold chain, part of which could at least be used to transport other goods like agricultural produce”.