And then, at the dawn of bacteriology, developments rapidly followed. Antitoxins and vaccines against diphtheria, tetanus, anthrax, cholera, plague, typhoid, tuberculosis, and more were developed through the s. The middle of the 20 th century was an active time for vaccine research and development.
Methods for growing viruses in the laboratory led to rapid discoveries and innovations, including the creation of vaccines for polio. Researchers targeted other common childhood diseases such as measles, mumps, and rubella, and vaccines for these diseases reduced the disease burden greatly.
Pertussis vaccine development took considerably longer, with a whole cell vaccine first licensed for use in the US in Viral tissue culture methods developed from , and led to the advent of the Salk inactivated polio vaccine and the Sabin live attenuated oral polio vaccine.
Mass polio immunisation has now eradicated the disease from many regions around the world. Progess of polio elimination and Image:CDC. Attenuated strains of measles, mumps and rubella were developed for inclusion in vaccines. Measles is currently the next possible target for elimination via vaccination.
Despite the evidence of health gains from immunisation programmes there has always been resistance to vaccines in some groups. The late s and s marked a period of increasing litigation and decreased profitability for vaccine manufacture, which led to a decline in the number of companies producing vaccines. During the s, one vaccine was eliminated. Because of successful eradication efforts, the smallpox vaccine was no longer recommended for use after While vaccine research continued, new vaccines were not introduced during the s.
The vaccine for Haemophilus influenzae type b was licensed in and placed on the recommended schedule in When the schedule was published again in , the hepatitis B vaccine had been added. The hepatitis B vaccine was not new, as it had been licensed in and recommended for high-risk groups such as infants whose mothers were hepatitis B surface antigen positive, healthcare workers, intravenous drug users, homosexual men and people with multiple sexual partners.
However, immunization of these groups didn't effectively stop transmission of hepatitis B virus. The change of recommendation to immunize all infants in was the result of these failed attempts to control hepatitis B by only immunizing high-risk groups. Following this recommendation, hepatitis B disease was virtually eliminated in children less than 18 years of age in the United States.
As more vaccines became available, an annual update to the schedule was important because of changes that providers needed to know, such as detailed information about who should receive each vaccine, age s of receipt, number of doses, time between doses, or use of combination vaccines. New vaccines were also added.
Annual updates to both the childhood and adult immunization schedules offer guidance to healthcare providers in the form of new recommendations, changes to existing recommendations, or clarifications to assist with interpretation of the schedule in certain circumstances. In the early s, four vaccines were available: diphtheria, tetanus, pertussis and smallpox. Because three of these vaccines were combined into a single shot DTP , children received five shots by the time they were 2 years old and not more than one shot at a single visit.
By the mids, seven vaccines were available: diphtheria, tetanus, pertussis, measles,mumps, rubella and polio. Because six of these vaccines were combined into two shots DTP and MMR , and one, the polio vaccine, was given by mouth, children received five shots by the time they were 2 years old and not more than one shot at a single visit.
Each type of vaccine listed below works in a slightly different way, yet all contain some portion of the virus or bacteria so that our immune systems may build up a defense against them in case you ever come into contact with the real thing. Let's take a specific example of a type of vaccine: the attenuated virus. An attenuated virus vaccine contains the weakened viral particle, making it non-infectious when administered. Figure 2: Basic reproduction numbers R0 of various diseases.
R0 indicates transmissibility of a disease by averaging how many people would be infected by one contagious person. Of these diseases, measles and smallpox have been declared eliminated by the WHO.
Each virus has a number that is assigned based on how infectious it is, as shown in Figure 2. R 0 helps scientists figure out what percentage of our population needs to be immune to the virus — either by having survived infection or by having been vaccinated — in order to prevent other, more vulnerable people in our population from becoming infected with the virus and experiencing a much more severe case of the disease.
Figure 3: Schematic of Herd Immunity. The person in purple is an infectious patient, people in blue are people who are not immune to the disease, and people who are in green are immune. As more people become immune there are less people becoming infected by the initial purple patient.
This is how herd immunity works. Thankfully, in the case of measles that has happened! By , enough of the population had become immune to measles by receiving the vaccine — not by having contracted measles — that it was classified as an eliminated virus by the World Health Organization. This ability for a population to be collectively safe from a virus by the majority of its constituents being vaccinated is called herd immunity.
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