Herd immunity threshold percentages explained: how the concept works, how it's calculated, and where vaccine-induced immunity may fall short of the theory.
"Herd immunity" (also called "community immunity") refers to the epidemiological principle that widespread immunity within a population — whether through natural infection or vaccination — can reduce pathogen transmission below the threshold needed to sustain outbreaks. According to Siri, the claim that vaccines can create herd immunity is only true for a narrow subset of vaccines — and is outright false for most vaccines currently mandated for school attendance in the United States.
Herd immunity requires a vaccine (or natural infection) to prevent transmission of the pathogen. Many vaccines reduce symptoms in the vaccinated individual but do not prevent the pathogen from replicating in or being shed by that person. For such vaccines, the concept of vaccine-induced herd immunity does not apply — by definition.
Siri argues that the entire mandate framework — expelling unvaccinated children from school to protect community health — collapses once the transmission question is examined vaccine by vaccine.
The only polio vaccine used in the United States since 2000. The CDC states on its own website that IPV "does not stop transmission of the virus" and "does not prevent intestinal infection and therefore does not prevent poliovirus transmission."
IPV is injected into the arm and creates IgG antibodies in the blood — not IgA antibodies in the intestinal tract where the polio virus replicates. An IPV-vaccinated child who encounters the polio virus can still be infected and still shed the virus in feces. The vaccine only prevents the virus from traveling from the gut into the bloodstream and spinal column.
Siri's conclusion: vaccinated children, having fewer or no symptoms, may be more likely to socialize while infectious — potentially spreading polio more than unvaccinated symptomatic children.
2013 FDA Baboon Study: FDA scientists divided baboons into three groups: (1) natural immunity (prior infection), (2) DTaP vaccinated, (3) naïve (no prior exposure). All were then exposed to pertussis bacteria. Results: the natural immunity group shed zero pertussis bacteria. The vaccinated group and the naïve group shed at comparable levels — in fact, vaccinated baboons shed for 42 days vs. 38 days for the naïve group.
2018 World Consensus Conference: Sixteen world-leading pertussis experts (including Kathryn Edwards and Tina Tan, both with documented financial ties to Sanofi and GSK) issued a consensus paper stating explicitly:
> "aPV pertussis vaccines do not prevent colonization. Consequently, they do not reduce the circulation of B. pertussis and do not exert any herd immunity effect."
The paper also noted: "the lack of mucosal immune responses after aPV administration favor infection, persistent colonization, and transmission of the pathogen."
GSK "Big Bad Cough" Campaign: GSK ran an advertising campaign depicting grandmothers as wolves who would harm their grandchildren by not being vaccinated for pertussis. ICAN's firm brought a class action lawsuit against GSK for consumer fraud and false advertising. The entire campaign was pulled by mid-September 2020 following service of the lawsuit. GSK's website had previously told adults to "receive a booster at least 2 weeks before having close contact with an infant" — this statement was scrubbed after the lawsuit.
The CDC states: "Tetanus is not contagious from person-to-person." The tetanus vaccine is a toxoid — it creates antibodies only to the toxin sometimes released by the tetanus bacterium, not to the bacterium itself. Therefore, the tetanus vaccine cannot prevent transmission (the bacterium doesn't transmit person-to-person) and also cannot prevent colonization by the bacterium.
Also a toxoid vaccine — creates antibodies only to the diphtheria toxin, not to the diphtheria bacterium. Does not prevent colonization or transmission of the bacterium.
CDC states: "Much of the decline [in meningococcal disease] occurred before the routine use of MenACWY vaccines. … Data suggest MenACWY vaccines have provided protection to those vaccinated, but probably not to the larger, unvaccinated community (population or herd immunity)." Protection wanes in most adolescents within 5 years; CDC does not recommend routine adult administration.
Hep B is transmitted primarily through sexual contact and contaminated needles — not school-based activities. ICAN submitted a FOIA request to CDC for "documentation sufficient to reflect any case(s) of transmission of Hepatitis B in an elementary, middle, or high school setting." CDC's response: it could not identify a single such case.
These vaccines can prevent transmission (at least in some people for some period). However, eliminating these childhood infections may have caused more deaths (from cardiovascular disease, cancer) than they prevented.
Ontario, Canada: Starting December 2021, Ontario's health dashboard showed the fully vaccinated had higher case rates per 100,000 than the unvaccinated. As the gap widened (vaccinated far more likely to be infected), Ontario changed the chart's categories — replacing "unvaccinated" with "Not fully vaccinated" (which included partially vaccinated). By April 2022, the data showed the fully vaccinated had the highest case rates, boosted had the second highest, and "Not fully vaccinated" the lowest.
Scotland: Scotland's health authority published data showing vaccinated individuals (2-dose) had 2–3x higher case rates than the unvaccinated in December 2021 – January 2022. Scotland subsequently stopped publishing these reports.
Siri's conclusion: "when the data doesn't fit the dogma, the vaccinologists and public 'health' agencies will stop collecting and/or reporting the data."
Siri argues that vaccine mandates for school attendance are unjustifiable for most mandated vaccines because:
1. Most mandated vaccines (IPV, DTaP, tetanus, diphtheria, MenACWY) do not prevent transmission
2. For pertussis specifically, vaccinated individuals may be more likely to spread the pathogen
3. Hep B is not transmissible in a school setting (per CDC's own records)
4. Mandating a vaccine that only provides personal protection — not community protection — cannot be justified on public health grounds; it becomes a matter of forcing compliance with a belief system
If the logic of vaccine mandates were applied consistently, it would require excluding DTaP-vaccinated children from school (as they can spread pertussis) rather than unvaccinated children.
Polio History and Vaccine Narrative, Childhood Vaccine Schedule, Pre-Licensure Safety Testing, Kathryn Edwards, Tina Tan, GSK, ICAN
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