So what is herd immunity? Herd immunity is defined as ”...the protection of populations from infection which is brought about by the presence of immune individuals.” From “Herd immunity: History, theory, practice”.
This author will focus on pertussis and measles for the sake of this article because there are outbreaks each year.
Throughout each main point there will be comparison of vaccine induced immunity and natural immunity, allowing a more detailed analysis to be made by the reader. We shall primarily be sticking to 1st world conditions to rule out mitigating circumstances such as poor nutrition and lack of access to clean water.
The difficulty in producing an effective herd immunity from vaccines can be reduced to several major points.
- Duration of immunity is naturally variable and is notably shorter in vaccinees.
- Adults are highly unlikely to stay up to date on boosters.
- Rate of success in acquiring immunity is less in vaccinees when compared to natural immunity.
- Viral mutation and bacterial strain selection.
There are examples going back at least 30 years of measles (and other) outbreaks occurring in highly vaccinated (90% - 98%) populations:
Measles Outbreak among Vaccinated High School Students -- Illinois (1983 - 84)
“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).”
Measles outbreak in a fully immunized secondary-school population. (1987)
“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.”
An evaluation of measles serodiagnosis during an outbreak in a vaccinated community. (1988)
“A history of prior vaccination is not always associated with immunity nor with the presence of specific antibodies.”
Explosive school-based measles outbreak: intense exposure may have resulted in high risk, even among revaccinees. (1989)
“Even high levels of measles vaccination coverage have not always prevented outbreaks of measles spread by airborne transmission. It has been suggested that a large inoculum might increase vaccine failure risk.”
Measles Outbreak Among School-Aged Children -- Juneau, Alaska, 1996
“Of the 63 case-patients, 33 (52%) had received only one dose of MCV on or after their first birthday, and 30 (48%) had never been vaccinated with MCV.”
Outbreak of measles among persons with prior evidence of immunity, New York City, 2011.
“The index patient had 2 doses of measles-containing vaccine; of 88 contacts, 4 secondary patients were confirmed who had either 2 doses of measles-containing vaccine or a past positive measles IgG antibody.”
Largest Measles Epidemic in North America in a Decade—Quebec, Canada, 2011: Contribution of Susceptibility, Serendipity, and Superspreading Events
“Active surveillance in the most affected high school detected more than twice (130% increase) the number of cases in 2-dose recipients than initially reported, increasing their contribution to the total from 30% to 48% (Table 1).”
There are more outbreaks documented in the intervening years in both fully vaccinated and under or un-vaccinated communities around the world. These particular outbreaks were chosen for their clarity in illustration and creating a fuller timeline.
What follows is a similar set of outbreaks for pertussis along a similar timeline.
Persistence of pertussis in an immunized population: Results of the Nova Scotia Enhanced Pertussis Surveillance Program (Pub 1989)
“Most (91%) patients had received at least three doses of pertussis vaccine; vaccine efficacy was estimated at 45%. “
The 1993 epidemic of pertussis in Cincinnati. Resurgence of disease in a highly immunized population of children.
“Immunization records revealed that 74 percent (75 of 101) of the children with pertussis who were 19 months to 12 years old had received four or five doses of the combined diphtheria-pertussis-tetanus (DPT) vaccine, and that 82 percent (103 of 126) of those 7 to 71 months old had received at least three doses of DPT vaccine.”
Pertussis outbreak in recently vaccinated children in a kindergarten in Ljubljana during a resurgence in pertussis incidence (2005)
“The children in the kindergarten group were between one and two years old. All the children had been immunised with three doses of DTP(acellular)-HiB. Less than a year had passed since the last immunisation.”
Once again these outbreaks were chosen for clarity of illustration and fewer examples are given for brevities sake.
As we know, the news covers outbreaks of both diseases each year. Severity varies from year to year, but outbreaks are still happening. Vaccination rates are generally high in the USA and Canada. However there is mounting evidence of limited duration from the immunity garnered from vaccination, as well as incomplete effectiveness in producing even limited immunity.
Pertussis in particular is known to have limited effect and durability for vaccine induced immunity. Examples are linked below.
Estimating the Effectiveness of Tetanus-Diphtheria-Acellular Pertussis Vaccine (Tdap) for Preventing Pertussis: Evidence of Rapidly Waning Immunity and Difference in Effectiveness by Tdap Brand
“Tdap VE decreased with increasing time since receipt, with VEs of 75.3% (95% confidence interval [CI], 55.2%–86.5%) for receipt during 2012, 68.2% (95% CI, 60.9%–74.1%) for receipt during 2011, 34.5% (95% CI, 19.9%–46.4%) for receipt during 2010, and 11.9% (95% CI, −11.1% to 30.1%) for receipt during 2009/2008”
Effectiveness of pertussis vaccines for adolescents and adults: case-control study
“The adjusted estimate of effectiveness of Tdap vaccination against pertussis was 53.0% (95% confidence interval 41.9% to 62.0%) in the comparison with PCR controls, and 64.0% (55.5% to 70.9%) in the comparison with Kaiser Permanente Northern California controls.”
Unexpectedly Limited Durability of Immunity Following Acellular Pertussis Vaccination in Preadolescents in a North American Outbreak
“The vaccine effectiveness was 41%, 24%, and 79% for children aged 2–7 years, 8–12 years, 13–18 years, respectively.”
Waning Protection after Fifth Dose of Acellular Pertussis Vaccine in Children
“In the primary analysis comparing PCR-positive children with PCR-negative controls, with adjustment for calendar time, age, sex, race or ethnic group, and medical service area, the odds ratio for pertussis was 1.42 per year (95% CI, 1.21 to 1.66), indicating that each year after the fifth dose of DTaP was associated with a 42% increased odds of acquiring pertussis. A secondary analysis comparing PCR-positive cases with matched controls yielded similar results”
This is contrasted against the duration of naturally acquired immunity (lasting up to 30 years or more)
Estimating the Duration of Pertussis Immunity Using Epidemiological Signatures
“Our analysis found that a range of durations of naturally acquired immunity is consistent with pre-vaccine and vaccine era data. If repeat infections are as infectious as primary infections with no immune-boosting then this range is 60-100 years, if they are half as infectious, then this range is 30-80 years. These values are robust to changes in primary-repeat contact rates and variation in the reporting rate of repeat infections.”
Duration of Immunity Against Pertussis After Natural Infection or Vaccination
“The mean time between the first and second infections was 7.1 years [95% confidence interval (95% CI), 6.6–7.6)] in the unvaccinated children and 5.1 years (95% CI 4.5–5.7) in the previously vaccinated children.”
Duration of vaccine induced immunity for measles is notably longer than pertussis, lasting around 15 years. However this is still in contrast to the duration of naturally acquired immunity, which is currently believed to last for the duration of a person’s lifetime.
Duration of immunity following immunization with live measles vaccine: 15 years of observation in Zhejiang Province, China
“ Blood samples were taken from the study children every March for the 15 years of the investigation. The HI antibody titre declined markedly in the first year, continued to decrease gradually from the second to the fourth year, and thereafter remained steady at a low level (Fig. 1).”
Persistence of Measles Antibodies After 2 Doses of Measles Vaccine in a Postelimination Environment
“Measles antibody persisted in all vaccinees available for follow-up 10 years after a second dose of vaccine, with no seronegative results detected. Declining titers suggest the need for vigilance in ensuring disease protection for the vaccinated population.”
As compared to natural immunity;
Duration of Humoral Immunity to Common Viral and Vaccine Antigens
“...43 of the 45 subjects (96%) were seropositive, with a putative protective level of at least 0.2 IU of antimeasles antibodies per milliliter 23 in 41 subjects (91%) (Fig. 1B in the Supplementary Appendix). The decrease in measles-specific antibodies (Figure 1B) was not significant (P=0.94) and is likely to be maintained for life (estimated half-life, 3014 years; 95% CI, 104 to infinity).”
Adults are highly unlikely to stay up to date on boosters.
Resulting in poor transmission of immunity from mothers to their newborns. This is of significant concern for any parent for what is, this author hopes, obvious reasons.
Early Loss of Passive Measles Antibody in Infants of Mothers With Vaccine-Induced Immunity
“All infants with detectable measles antibody at 9 or 12 months had mothers born before 1963, before the vaccine era, and both maternal and cord blood measles geometric mean titers decreased significantly with decreasing maternal age.”
Early waning of maternal measles antibodies in era of measles elimination: longitudinal study
“Infants of vaccinated women had significantly lower antibody concentrations than did infants of naturally immune women (P<0.001 at all ages over the follow-up period).”
Comparative Analysis of Titers of Antibody against Measles Virus in Sera of Vaccinated and Naturally Infected Japanese Individuals of Different Age Groups
“Neutralizing (NT) antibody titers induced by vaccination were 2 times lower than those induced by natural infection and declined significantly by age 20.”
A vaccinated individual has the potential to become an asymptomatic carrier of the disease and spread it to those who are vulnerable. As can be seen in point 4, the vaccine is helping to force the pertussis bacterium to adapt and as a result create more potent strains.
Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model
“Baboons vaccinated with aP were protected from severe pertussis-associated symptoms but not from colonization, did not clear the infection faster than naïve animals, and readily transmitted B. pertussis to unvaccinated contacts.”
Rate of success in acquiring immunity is less in vaccines when compared to natural immunity.
Package inserts have detailed information for rates of success in acquiring neutralizing antibody titers in the clinical trials sections of the inserts. You can view them here:
Natural infections consistently produce more robust antibody titers. Some of the studies already linked show the differences in antibody response between vaccinated and naturally infected individuals.
The study linked below is used as an illustration to the point being made.
“Natural infection with wild virus was shown to induce more vigorous immune responses than did either vaccine…”
Viral mutation and bacterial strain selection.
Genetic Analysis of Measles Viruses Isolated in the United States, 1995–1996
“Genetic analysis was conducted on 28 wild type measles viruses isolated from outbreaks or cases in the United States during 1995–1996. These viruses were members of at least 6 distinct genetic groups. However, none of these viruses was related to the group 2 viruses that were associated with the resurgence of measles in the United States between 1989 and 1992 except for a single importation from the Philippines.
Adaptation of bordetella pertussis to vaccination: a cause for its reemergence?
“Widespread vaccination was introduced in The Netherlands in 1953, and we assumed that the B. pertussis population was not significantly affected by vaccination from 1949 to 1954 (defined as the prevaccination period in Figure 2). Notable differences were found between the populations from the prevaccination era and the subsequent period, both in the type and frequency of fingerprint types (e.g., the major fingerprint type found in strains collected from 1965-1972 [Ft-29] was absent during the prevaccination period). These qualitative observations were confirmed by the trend in genotypic diversity (Figure 2).”
Acellular pertussis vaccination enhances B. Parapertussis colonization
“We show that aP vaccination helped clear B. pertussis but resulted in an approximately 40-fold increase in B. parapertussis lung colony-forming units (CFUs). Such vaccine-mediated facilitation of B. parapertussis did not arise as a result of competitive release; B. parapertussis CFUs were higher in aP-relative to sham-vaccinated hosts regardless of whether infections were single or mixed. Further, we show that aP vaccination impedes host immunity against B. parapertussis—measured as reduced lung inflammatory and neutrophil responses. Thus, we conclude that aP vaccination interferes with the optimal clearance of B. parapertussis and enhances the performance of this pathogen. Our data raise the possibility that widespread aP vaccination can create hosts more susceptible to B. parapertussis infection.”
Global Population Structure and Evolution of Bordetella pertussis and Their Relationship with Vaccination
“We show that global transmission of new strains is very rapid and that the worldwide population of B. pertussis is evolving in response to vaccine introduction, potentially enabling vaccine escape.”
Insight into evolution of Bordetella pertussis from comparative genomic analysis: evidence of vaccine-driven selection.
“Our findings suggest that B. pertussis, despite its high population homogeneity, is evolving in response to vaccination pressure with recent expansion of clones carrying variants of genes encoding ACV antigens.”
Rapid Increase in Pertactin-deficient Bordetella pertussis Isolates, Australia
“These findings suggest that B. pertussis not expressing prn arose independently multiple times since 2008, rather than by expansion of a single prn-negative clone. All but 1 isolate had ptxA1, prn2, and ptxP3, the alleles representative of currently circulating strains in Australia. This pattern is consistent with continuing evolution of B. pertussis in response to vaccine selection pressure.”
Health Care–Associated Measles Outbreak in the United States After an Importation: Challenges and Economic Impact
“On 12 February 2008, an infected Swiss traveler visited hospital A in Tucson, Arizona, and initiated a predominantly health care–associated measles outbreak involving 14 cases.”
Measles: Global Update
“The Americas, including Canada, have experienced outbreaks of measles, when the virus has been imported from other regions.”
The need for more effective prevention and therapy for highly communicable diseases is becoming more evident in light of waning immunity in vaccinees. Particularly in the context of protecting especially young children and the growing number of immunocompromised individuals. In addition the cost of attempting to contain outbreaks cannot be ignored.
Healthcare-Associated Pertussis Outbreak in Arizona: Challenges and Economic Impact, 2011
“An outbreak investigation identified 15 pertussis cases among 5 infants and 10 healthcare professionals at 1 hospital’s neonatal intensive care unit (NICU). The cost of the outbreak to this hospital was $97,745.”
Effective therapies are already known for both pertussis and measles, though not widely.
The Vitamin C treatment for Whooping Cough ~ Suzanne Humphries, MD
THE THERAPEUTIC VALUE OF VITAMINS A & D IN MEASLES
Ascorbic Acid and Other Modern Analogs of the Germ Theory
In light of the knowledge shown above there may yet be an appropriate application of vaccination for specific diseases and their prevention in susceptible adults. For instance if a young woman wishes to have children and is seen to have no immunity to rubella then a single vaccine may be appropriate for her prior to conceiving. Or if a man has no immunity and no history of infection of mumps then a vaccination may be appropriate to reduce risks of complications if he is in an area with an outbreak occurring. In addition post exposure usage of immunoglobulin can be a very cost effective treatment as well. Particularly considering that if an individual is infected then vaccination is ineffective at such time.
To finish off this article, this is a fascinating study on the evolutionary perspective of the development of long term immunity:
Evolution of the temporal persistence of immune protection
“The evolution of resistance to parasites has been the focus of numerous theoretical studies and several mechanisms, ranging from innate to acquired immune responses, have been considered. Life-history theory predicts that long-lived species should invest more resources into maintenance and immunity than short-lived species. Here, we provide further theoretical and empirical support for this hypothesis. First, an analysis of the evolution of the persistence of immune protection in a theoretical framework accounting for maternal transfer of immunity reveals that longer-lived hosts are expected to invest in more persistent intragenerational and transgenerational immune responses. Controlling for phylogenetic structure and for the confounding effect of catabolic activity, we further showed that immunoglobulin half-life and longevity are positively correlated in mammal species. Our study confirms that persistence of immunity has evolved as part of elaborate anti-parasitic defence strategies.”