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What is Herd Immunity?


A situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the disease has little opportunity to spread within the community.


    Vaccination and herd immunity: what more do we know?

    Rashid H, et al. Curr Opin Infect Dis. 2012.

    RECENT FINDINGS: The conventional idea of herd immunity is based on the relationship between the transmission dynamics of infectious agents and population immunity. However, there have been some recent conceptual developments in vaccine 'herd immunity' or 'herd protection' that address the complexities of imperfect immunity, heterogeneous populations, nonrandom vaccine uptake and 'freeloaders'. Some vaccines may provide better protection than others; for instance, meningococcal conjugate vaccines are superior to polysaccharide vaccines, as is true of pneumococcal and Haemophilus influenzae type b vaccines. Achieving a very high uptake rate should be the target for certain vaccines, for example, measles vaccine, in order to prevent the disease effectively. Emerging issues, for example, waning of immunity after pertussis vaccination, are fresh challenges.



    Major measles epidemic in the region of Quebec despite a 99% vaccine coverage

    Boulianne N

    The 1989 measles outbreak in the province of Quebec has been largely attributed to an incomplete vaccination coverage. In the Quebec City area (pop. 600,000) 1,363 confirmed cases of measles did occur. A case-control study conducted to evaluate risk factors for measles allowed us to estimate vaccination coverage. It was measured in classes where cases did occur during the outbreak. This population included 8,931 students aged 5 to 19 years old. The 563 cases and a random sample of two controls per case selected in the case's class were kept for analysis. The vaccination coverage among cases was at least 84.5%. Vaccination coverage for the total population was 99.0%. Incomplete vaccination coverage is not a valid explanation for the Quebec City measles outbreak.


  • “Herd Immunity.” The Flawed Science and Failures of Mass Vaccination

    Dr. Suzanne Humphries

    he oft-parroted sound bite – “we need herd immunity”- implies that if ninety five percent of the population can become “immune” to a disease via vaccination, target immunity levels will be met and diseases will either be eradicated or controlled. This sound bite is the most commonly pulled weapon used by the vaccinators, only second to “smallpox and polio were eradicated by vaccination.” “Herd immunity” is the trump card for the defense of vaccination on TV, Internet, medical journals and newspapers as to why we should be vaccinated over and over throughout our lives, with an ever-increasing number of vaccines.



    Whether Vaccinated People Can Infect Unvaccinated People

    Barbara Loe Fisher

    Public health officials say that unvaccinated children pose a big danger to those around them and even threaten the health of fully vaccinated children and adults because vaccines can fail to prevent infection in vaccinated persons. Today, the most common argument used to justify ‘no exceptions’ mandatory vaccination laws is that unvaccinated people pose a serious health threat to others who “cannot be vaccinated,” such as the immune-compromised.


    Some parents of unvaccinated children are asking the opposite question: Could my unvaccinated or immune compromised child get sick from coming in contact with a recently vaccinated person? When it comes to live virus vaccines, the short answer is: Yes.



    Herd Immunity: Fact or Fiction?

    Dr. Kelly Brogan

    I see myself as a protector of women and children, a gatekeeper of sorts. For this reason, I bristle at the tactics of coercion used to move women out of their space of intuitive agency, and into a place of fear. There is no tactic as powerful as altruistic guilt, as insinuating that a woman is dangerous, reckless, and selfish if she chooses not to vaccinate herself or her child. The most prevalent and most unsubstantiated meme is that of “herd immunity” or the notion that high vaccination compliance protects a community from an outbreak.


    A brilliant commentary by Cornell, Harvard, and Stanford vetted immunologist, is a must read on the subject, for anyone  intending to wield the “greater good” rhetoric, or who has been subject to the scorn of those who do. Here is an overview of the matter according to Dr. Obukhanych.



    Junk Science Week: Vaccinating the ‘herd’

    Lawrence Solomon

    “When vaccination rates are very high, as they still are in the nation as a whole, everyone is protected,” explained USA Today in a recent editorial entitled “Vaccine opt-outs put public health at risk.”


    “This ‘herd immunity’ protects the most vulnerable, including those who can’t be vaccinated for medical reasons, infants too young to get vaccinated and people on whom the vaccine doesn’t work. But herd immunity works only when nearly the whole herd joins in. When some refuse vaccinations and seek a free ride, immunity breaks down and everyone is more vulnerable.”


    The concept of “herd immunity” first materialized in the 1930s, when Johns Hopkins University’s Arthur Hedrich discovered that, after 55% of Baltimore’s population acquired measles (and thus immunity to measles), the rest of the population, or “herd,” became protected. This concept provides today’s rationale for insisting that everyone be vaccinated.


    “If you only risked your own health by not getting vaccinated, that would be your business,” mass vaccination advocates state. “But when your failure to get vaccinated endangers me or my child, that becomes my business.” It’s a powerful argument, except for one thing — herd immunity in vaccinated populations has been repeatedly disproven.




    Lawrence Solomon: The untold story of measles

    Lawrence Solomon

    Early in the last century, measles killed millions of people a year. Then, bit by bit in countries of the developed world, the death rate dropped, by the 1960s by 98% or more. In the U.K., it dropped by an astounding 99.96%. And then, the measles vaccine entered the market.


    After the vaccine’s introduction, the measles death rate continued to drop into the 1970s. Many scientists credit the continued decline entirely to the vaccine. Other scientists believe the vaccine played a minor role, if that, noting that most infectious diseases similarly petered out during the 20th century, including some, like scarlet fever, for which vaccines were never developed.


    The credit for the century-long decline, scientists generally agree, goes to improved nutrition and improved health care, side effects of the West’s growing affluence. In the U.S., the death rate dropped by about 98%, from about 10 per 100,000 population a century ago to one fifth of one person by 1963, the year measles vaccines made their American debut. Both before and after vaccination started, victims tended to be poor.




    The Deadly Impossibility Of Herd Immunity Through Vaccination

    Dr. Russel Blaylock

    Those who are observant have noticed a dangerous trend in the United States, as well as worldwide, and that is the resorting of various governments at different levels to mandating forced vaccination upon the public at large. My State of Mississippi has one of the most-restrictive vaccine-exemption laws in the United States, where exemptions are allowed only upon medical recommendation. Ironically, this is only on paper, as many have had as many as three physicians, some experts in neurological damage caused by vaccines, provide written calls for exemption, only to be turned down by the State’s public-health officer.


    Worse are the States, such as Massachusetts, New Jersey and Maryland, where forced vaccinations have either been mandated by the courts, the state legislature, or have such legislation pending. All of such policies strongly resemble those policies found in National Socialist empires, Stalinist countries, or Communist China.



    Whooping Cough Resurgence Due to Vaccinated People Not Knowing They're Infectious?

    Santa Fe Institute

    Whooping cough has made an astonishing comeback, with 2012 seeing nearly 50,000 infections in the U.S. (the most since 1955), and a death rate in infants three times that of the rest of the population. The dramatic resurgence has puzzled public health officials, who have pointed to the waning effectiveness of the current vaccine and growing anti-vaccine sentiment as the most likely culprits.



    19 Kids in Summit Co. Diagnosed With Whooping Cough Despite Being Up to Date on Vaccinations

    Kiersten Nunez

    PARK CITY, Utah — A whooping cough outbreak is causing concern in Summit County as 19 children have been diagnosed, and it’s the first time in years Park City schools have seen a case of pertussis.


    Officials said all of the children who have been diagnosed were vaccinated against the illness.


    “It has been a very busy week, very busy week here, a lot of people coming in to be tested,” said Dr. Alison Delgado with Summit Pediatrics.


    Delgado tested dozens of children for whooping cough in the last week. According to the Summit County Department of Health, there are 19 confirmed cases of the highly contagious illness in Park City, and all of the children infected are up to date on their vaccinations.


    “A lot of people want to know why their child is getting it because they’re vaccinated, and it has to do a lot with the vaccine; it’s not a 100 percent, however it is about 90 to 95 percent effective,” said Carolyn Rose, who is a nursing director for the Summit County Department of Health.


    What starts with cold-like symptoms quickly escalates into a severe cough. Rose said since the children were immunized, the illness won’t hit them as hard and they aren’t as contagious.



    Asymptomatic Transmission and the Resurgence of Bordetella Pertussis

    Benjamin M. Althouse and Samuel V. Scarpino

    Many countries have seen a startling increase in the incidence of Bordetella pertussis, an important causative agent of whooping cough, over the past 20 years [1]. In the United States (US), 2012 saw more diagnosed B. pertussis cases than in any year since 1955 (Fig. 1 and [2], accessed 20 January 2015). The United Kingdom (UK) has seen a similarly startling rise, with more cases occurring in 2013 than since the vaccine refusal era of the 1970s and 1980s (data available here: [3], accessed 20 January 2015). Two general hypotheses have been proposed to explain the rise in B. pertussis incidence: either vaccination cov- erage is too low, where individuals remain unvaccinated or unvaccinated susceptible individuals move into popu- lations; or vaccinated individuals can still become infected [1, 4]. While vaccination coverage has likely played a role in increasing incidence, coverage has historically been high [1, 5], raising the likelihood that the resurgence is — at least in part — due to low vaccine effectiveness [6].



    Pertussis Infection in Fully Vaccinated Children in Day-Care Centers, Israel

    Isaac Srugo

    Pertussis, an acute disease of the upper respiratory tract caused by the gram-negative bacillus Bordetella pertussis, lasts 6 to 8 weeks and has three clinical stages. The initial (catarrhal) stage resembles a common cold with a mild cough. The second (paroxysmal) stage is characterized by episodes of repetitive coughing during a single expiration, followed by a sudden inspiration that generates the typical "whoop." The final (convalescent) stage, which lasts 1 to 2 weeks, marks a decrease in the severity and frequency of the cough.


    Since the introduction of routine childhood vaccine, pertussis has been considered preventable, and pertussis-associated illness and deaths are uncommon (2). However, vaccine-induced immunity wanes after 5 to 10 years, making the vaccinated host vulnerable to infection (3). This susceptibility has been described in outbreaks of pertussis infection in highly vaccinated populations (3-6).



    Public Health Officials Know: Recently Vaccinated Individuals Spread Disease


    Washington, D.C., March 3, 2015 (GLOBE NEWSWIRE) -- Physicians and public health officials know that recently vaccinated individuals can spread disease and that contact with the immunocompromised can be especially dangerous. For example, the Johns Hopkins Patient Guide warns the immunocompromised to "Avoid contact with children who are recently vaccinated," and to "Tell friends and family who are sick, or have recently had a live vaccine (such as chicken pox, measles, rubella, intranasal influenza, polio or smallpox) not to visit."


    A statement on the website of St. Jude's Hospital warns parents not to allow people to visit children undergoing cancer treatment if they have received oral polio or smallpox vaccines within four weeks, have received the nasal flu vaccine within one week, or have rashes after receiving the chickenpox vaccine or MMR (measles, mumps, rubella) vaccine.


    "The public health community is blaming unvaccinated children for the outbreak of measles at Disneyland, but the illnesses could just as easily have occurred due to contact with a recently vaccinated individual," says Sally Fallon Morell, president of the Weston A. Price Foundation. The Foundation promotes a healthy diet, non-toxic lifestyle and freedom of medical choice for parents and their children. "Evidence indicates that recently vaccinated individuals should be quarantined in order to protect the public."




    Measles Outbreak among Vaccinated High School Students -- Illinois


    From December 9, 1983, to January 13, 1984, 21 cases of measles occurred in Sangamon County, Illinois.* Nine of the cases were confirmed serologically. The outbreak involved 16 high school students, all of whom had histories of measles vaccination after 15 months of age documented in their school health records. Of the five remaining cases, four occurred in unvaccinated preschool children, two of whom were under 15 months of age, and one case occurred in a previously vaccinated college student (Figure 5).


    The affected high school had 276 students and was in the same building as a junior high school with 135 students. A review of health records in the high school showed that all 411 students had documentation of measles vaccination on or after the first birthday, in accordance with Illinois law.


    Measles vaccination histories were obtained from the school health records of all 276 senior high school students. Risk of infection was not significantly associated with type of vaccine, medical provider, age at most recent vaccination, or revaccination. All the students with measles had received their most recent vaccinations after 15 months of age. However, the measles attack rate increased with increasing years since most recent vaccination (p = 0.024) (Table 3). The attack rate was four times greater for students vaccinated 10 or more years before the outbreak than for students vaccinated more recently (p 0.05). When these data are corrected for the number of vaccinations, the trend was still observed and achieved a borderline level of statistical significance (p = 0.07). Age at first or last vaccination was not a confounding variable.



    Measles Outbreak in a Fully Immunized Secondary-School Population

    The New England Journal of Medicine


    An outbreak of measles occurred among adolescents in Corpus Christi, Texas, in the spring of 1985, even though vaccination requirements for school attendance had been thoroughly enforced. Serum samples from 1806 students at two secondary schools were obtained eight days after the onset of the first case. Only 4.1 percent of these students (74 of 1806) lacked detectable antibody to measles according to enzymelinked immunosorbent assay, and more than 99 percent had records of vaccination with live measles vaccine. Stratified analysis showed that the number of doses of vaccine received was the most important predictor of antibody response. Ninety-five percent confidence intervals of seronegative rates were 0 to 3.3 percent for students who had received two prior doses of vaccine, as compared with 3.6 to 6.8 percent for students who had received only a single dose. After the survey, none of the 1732 seropositive students contracted measles. Fourteen of 74 seronegative students, all of whom had been vaccinated, contracted measles. In addition, three seronegative students seroconverted without experiencing any symptoms.


    We conclude that outbreaks of measles can occur in secondary schools, even when more than 99 percent of the students have been vaccinated and more than 95 percent are immune.


Media Resources

Herd Immunity: Is it Irresponsible Not to Vaccinate?

Dr. Tenpenny Discusses Why Herd Immunity Doesn't Apply to Vaccines

Dr. Mercola and Barbara Loe Fisher on

Herd Immunity