Some vaccinations are given in a single dose, either orally or by injection, while others require multiple doses over a prescribed time period to provide maximum benefit. Most types of vaccination require a booster shot periodically as a kind of reminder to the immune system. Influenza vaccinations are given annually because each year different strains of influenza occur. It was also recommended that children already in school be vaccinated against hepatitis B when they are 11 or 12 until all school-age children are vaccinated. In underdeveloped and developing countries vaccinations have not been as available as in developed countries.
Vaccination is the single, most powerful method to control contagious diseases.
New techniques, including genetic engineering, are being explored to develop better, safer, and less expensive vaccines. Vaccination offers real hope for eliminating specific contagious disease from the planet. Smallpox , the deadly epidemic disease that killed millions and inspired Jenner, was declared eradicated in 1980. Global vaccination efforts may be able to repeat this achievement.