Vaccines can be administered orally, nasally or by injection: into the muscle mass, into the layer between skin and muscle or into the outer layer of skin. They stimulate an immune response that gives the body the ability to mount a swifter defence to the same pathogen if it is encountered again.
There are several types of vaccine in use, each with their own strengths and weaknesses. Many are administered along with adjuvants — substances such as aluminium salts, lipids and RNA that strengthen the immune response.
Vaccines initially developed in the 1950s and 1960s, such as those for polio and measles, are commonly administered globally. Those introduced more recently, such as that for rotavirus, are less widely used.
The luxury of hesitancy
Although 79% of people globally think that vaccines are safe, trust varies widely between nations. Europe has some of the lowest levels of perceived safety — a finding that might partly explain the surge in measles cases seen in Ukraine in 2018. But other factors besides hesitancy to vaccinate also affect the spread of infections.
Case numbers of certain infectious diseases in the United States dropped precipitously after effective vaccines for each were widely adopted.
Long road to new vaccines
Development programmes are under way for a number of deadly diseases that currently lack a vaccine. In many cases, the pathogen responsible was identified decades ago, but effective vaccination strategies have proved elusive.
Nature 575, S44-S45 (2019)