Question

L07: Describe "herd immunity" (BL2) & evaluate the effect of anti-vaccination on the risk to an average 60 year old, a partially vaccinated 2 year old, an unvaccinated infant, and the immune- compromised (BL6) LO8: Identify (BL1) and describe (BL2) the 5 stages of disease LO12: Postulate why certain increases or decreases in disease occur from epidemiological graphs (BL3

hered immunity disease

Answer 1

‘Herd immunity is a form of immunity that occurs when the vaccination of a significant portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity.’

When a high percentage of the population is vaccinated, it is difficult for infectious diseases to spread, because there are not many people who can be infected. For example, if someone with measles is surrounded by people who are vaccinated against measles, the disease cannot easily be passed on to anyone, and it will quickly disappear again. This is called ‘herd immunity’, 'community immunity' or 'herd protection', and it gives protection to vulnerable people such as newborn babies, elderly people and those who are too sick to be vaccinated.

Herd immunity does not protect against all vaccine-preventable diseases. The best example of this is tetanus, which is caught from bacteria in the environment, not from other people who have the disease. No matter how many people around you are vaccinated against tetanus, it will not protect you from tetanus.

People who depend on herd immunity

Some people in the community rely on herd immunity to protect them. These groups are particularly vulnerable to disease, but often cannot safely receive vaccines:

• People without a fully-working immune system, including those without a working spleen
• People on chemotherapy treatment whose immune system is weakened
• People with HIV
• Newborn babies who are too young to be vaccinated
• Elderly people
• Many of those who are very ill in hospital

For these people, herd immunity is a vital way of protecting them against life-threatening disease.

Vaccines are especially important for older adults. As you get older, your immune system weakens and it can be more difficult to fight off infections. You’re more likely to get diseases like the flu, pneumonia, and shingles — and to have complications that can lead to long-term illness, hospitalization, and even death.

If you have an ongoing health condition — like diabetes or heart disease — getting vaccinated is especially important. Vaccines can protect you from serious diseases (and related complications) so you can stay healthy as you age.

Getting vaccinated can help keep you, your family, and your community healthy.

Newborn infants are too young to receive many vaccines, either for safety reasons or because passive immunity renders the vaccine ineffective.^[16]Individuals who are immunodeficient due to HIV/AIDS, lymphoma, leukemia, bone marrow cancer, an impaired spleen, chemotherapy, or radiotherapy may have lost any immunity that they previously had and vaccines may not be of any use for them because of their immunodeficiency

Vaccines are typically imperfect as some individuals' immune systems may not generate an adequate immune response to vaccines to confer long-term immunity, so a portion of those who are vaccinated may lack immunity. Lastly, vaccine contraindications may prevent certain individuals from becoming immune. This varies depending on the germ and how contagious it is. The more contagious it is then the more people need to be vaccinated for herd immunity to work. For example, measles is very contagious. Before the use of the measles vaccine, every person with measles would infect another 10-15 people and so the disease would spread very quickly. To achieve herd immunity for measles at least 90-95% of the population need to be vaccinated. A disease like polio is less contagious, and 80-85% of the population would need to be vaccinated for herd immunity to work. Although this is lower it is still a very high proportion, especially given that some people cannot be vaccinated for medical reasons.

People who depend on herd immunity

Some people in the community rely on herd immunity to protect them. These groups are particularly vulnerable to disease, but often cannot safely receive vaccines:

• Newborn babies who are too young to be vaccinated
• Elderly people
• People without a fully-working immune system, including those without a working spleen(immune compromised)
• People with HIV

Herd Immunity and the Flu

Some vaccines are better at producing herd immunity than others. The measles, mumps, and rubella (MMR) vaccine is 97% effective at preventing measles. So when lots of people in a community get this vaccine, protection rates stay high.

The flu vaccine is a little different. It's only about 40% to 60% effective in any given year. That's because sometimes the virus strains in the vaccine don't exactly match the virus that spreads.

Even if the flu vaccine isn't perfect, it's still worth getting, Brady says. In any one flu season, the flu vaccine prevents millions of people from getting the flu. "That's particularly important when the people who don't get the flu are around people who are over 65, or have [other illnesses], or are young," he adds.

The flu vaccine is also good at protecting small groups of people -- such as in your home, office, or school. When you get vaccinated, you help an older adult relative who has a chronic disease, or a baby who is too young to get vaccinated avoid getting sick, Cohn says.

Vaccines are especially important for people who work in hospitals and other health care centers. The sick people they care for are more likely to get flu complications, and they need more protection.

Selective vaccination of groups that are important in transmission can slow transmission in general populations or reduce incidence among population segments that may be at risk of severe consequences of infection. Schools play an important role in community transmission of influenza viruses, and thus there has been discussion of slowing transmission either by closing schools or by vaccinating schoolchildren. Selective vaccination of schoolchildren against influenza was policy in Japan during the 1990s and was shown to have reduced morbidity and mortality among the elderly .

Chronic lymphocytic leukemia (CLL), on the other hand, does not usually form tumors. It's generally in the bone marrow and blood. And, in many cases, it has spread to other organs such as the spleen, liver, and lymph nodes by the time it's found. The outlook for a person with CLL depends on other information, such as the results of lab test and imaging tests.

Staging systems for chronic lymphocytic leukemia

A staging system is a standard way for the cancer care team to describe cancer. There are 2 different systems for staging CLL:

• Rai system: This is used more often in the United States.
• Binet system: This is used more widely in Europe.

Both of these staging systems are helpful and have been in use for many years.

Rai staging system

The Rai system is based on lymphocytosis. The patient must have a high number of lymphocytes in their blood and bone marrow that isn't linked to any other cause (like infection).

For a diagnosis of CLL, the overall lymphocyte count does not have to be high, but the patient must have at least 5,000/mm³ monoclonal lymphocytes (sometimes called a monoclonal lymphocytosis). Monoclonal means that the cancer cells all came from one original cell. This causes them to have the same chemical pattern which can be seen with special testing.

This system divides CLL into 5 stages based on the results of blood tests and a physical exam:

• Rai stage 0: Lymphocytosis; no enlargement of the lymph nodes, spleen, or liver; red blood cell and platelet counts are near normal.
• Rai stage I: Lymphocytosis; enlarged lymph nodes; spleen and liver are not enlarged; red blood cell and platelet counts are near normal.
• Rai stage II: Lymphocytosis; enlarged spleen (and maybe an enlarged liver); lymph nodes may or may not be enlarged; red blood cell and platelet counts are near normal.
• Rai stage III: Lymphocytosis; lymph nodes, spleen, or liver may or may not be enlarged; red blood cell counts are low (anemia); platelet counts are near normal.
• Rai stage IV: Lymphocytosis; enlarged lymph nodes, spleen, or liver; red blood cell counts may be low or near normal; platelet counts are low (thrombocytopenia).

Doctors separate the Rai stages into low-, intermediate-, and high-risk groups when determining treatment options.

• Stage 0 is low risk.
• Stages I and II are intermediate risk.
• Stages III and IV are high risk.

These risk groups are used later in Treatment of Chronic Lymphocytic Leukemia.

Binet staging system

In the Binet staging system, CLL is classified by the number of affected lymphoid tissue groups (neck lymph nodes, groin lymph nodes, underarm lymph nodes, spleen, and liver) and by whether or not the patient has anemia (too few red blood cells) or thrombocytopenia (too few blood platelets).

• Binet stage A: Fewer than 3 areas of lymphoid tissue are enlarged, with no anemia or thrombocytopenia.
• Binet stage B: 3 or more areas of lymphoid tissue are enlarged, with no anemia or thrombocytopenia.
• Binet stage C: Anemia and/or thrombocytopenia are present. Any number of lymphoid tissue areas may be enlarged.

Public health workers use epidemiologic principles as the foundation for disease surveillance and investigation activities. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problem

In descriptive epidemiology, data that describe the occurrence of the disease are collected by various methods from all relevant sources. The data are then collated by time, place, and person. Four time trends are considered in describing the epidemiologic data.

Analytic Epidemiology

The second epidemiologic method is analytic epidemiology, which analyzes disease determinants for possible causal relations. The two main analytic methods are the case-control (or case-comparison) method and the cohort method. The case-control method starts with the effect (disease) and retrospectively investigates the cause that led to the effect. The case group consists of individuals with the disease; a comparison group has members similar to those of the case group except for absence of the disease.

Epidemic Investigation

An epidemic investigation describes the factors relevant to an outbreak of disease; once the circumstances related to the occurrence of disease are defined, appropriate control and prevention measures can be identified. In an epidemic investigation, data are collected, collated according to time, place, and person, and analyzed and inferences are drawn

Descriptive Epidemiology

In descriptive epidemiology, data that describe the occurrence of the disease are collected by various methods from all relevant sources. The data are then collated by time, place, and person. Four time trends are considered in describing the epidemiologic data. The secular trend describes the occurrence of disease over a prolonged period, usually years; it is influenced by the degree of immunity in the population and possibly nonspecific measures such as improved socioeconomic and nutritional levels among the population.