Basic information on vaccines
Effectiveness of vaccines
The higher the proportion of the population that is vaccinated, the more effective the protection conferred by the vaccine. The majority of children in Finland receive all of the vaccines included in the National Vaccination Programme. This high vaccination coverage has led to the eradication of many dangerous diseases in Finland.
- Vaccines protect the recipient and the people in close contact with him or her. When a person does not get infected with a disease, he or she will also not pass it on to others. This way even those who are unvaccinated, such as children with cancer, are spared from the disease. This is known as herd immunity.
- The more contagious the disease is, the larger the population vaccination rate needs to be.
- If a vaccinated person is infected by a disease in spite of being previously vaccinated against it, the illness is usually less severe than it would be for an unvaccinated person. The risk of complications and serious sequelae is also reduced.
- Almost all vaccinations require multiple doses to achieve the desired level of immunity. It is important to get all of the doses in a vaccination protocol to achieve long-term, or even lifelong, protection against the disease in question.
- Some vaccines require boosters at regular intervals. These include the diphtheria-tetanus vaccine and the tick-borne encephalitis vaccine, for example. Influenza vaccines must be administered annually because influenza viruses evolve quickly and the previous year’s vaccine is unlikely to provide protection against the new strains.
- Vaccinations have achieved the worldwide eradication of smallpox, which is a very dangerous disease. The last case of smallpox was in 1977. The WHO is also trying to eradicate polio. One form of polio has already been eradicated from certain parts of the world.
- The National Vaccination Programme in Finland has reduced the prevalence of the MMR diseases, or measles, rubella and mumps, to only a few cases per year. Before immunisation, they afflicted thousands of people each year. Other diseases that are preventable by immunisation have also been similarly reduced by vaccinations.
Herd immunity
When a sufficiently high percentage of a population has been vaccinated and is immune to a given disease, that disease cannot spread. This also reduces the risk of infection for those who are not vaccinated. This is known as herd immunity.
Herd immunity varies between diseases. The more contagious the disease, the higher the vaccination coverage required for herd immunity. For example, the vaccination coverage for diphtheria needs to be at least 70 per cent, while the corresponding figure for measles is 95 per cent.
There are also diseases that cannot be eradicated by immunisation. The virus that causes tick-borne encephalitis lives mainly in non-human mammals and the continued existence of the disease cannot be changed by immunisation. Similarly, the tetanus bacteria lives in soil and infects people via cuts and broken skin. Herd immunity does not apply to these diseases because they are not infected from one person to another.
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