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Alum, an aluminum-based adjuvant or immune-enhancer used in many vaccines — including inactivated-virus COVID-19 vaccines — helps protect against the targeted (homologous) virus strain.

However, alum may raise infection risk from new (heterologous) virus strains, referred to as “breakthrough” infections, according to a preprint study published on Research Square.

Of the 13.5 billion COVID-19 vaccine doses administered globally, 5 billion used inactivated coronavirus as their active ingredient. Unlike the Pfizer and Moderna vaccines, inactivated-virus COVID-19 vaccines do not use mRNA. Instead, they use killed or weakened viruses to bring about the immune response.

Examples of virus-inactivated COVID-19 vaccines include China’s CoronaVac product, which was distributed in 40 countries, and the Indian COVAXIN product.

Alum also increases the risk for vaccine-associated enhanced respiratory disease (VAERD), a potentially life-threatening complication, after infection with a new strain. However, this effect disappears when alum is replaced by a different adjuvant, according to the study.

Researchers exposed vaccinated mice to two different virus strains

Researchers led by Mark Heise, Ph.D., an immunologist at the University of North Carolina, used laboratory mice to compare the effectiveness of an inactivated, alum-containing SARS-CoV-2 vaccine (iCoV2) against two coronaviruses: the strain for which the vaccine was designed, known as the homologous strain, and a previously unencountered (“heterologous”) coronavirus.

The test animals were bred specifically for susceptibility to coronavirus-induced lung disease.

The alum-containing vaccine protected against homologous (i.e., same virus) challenges with no apparent ill effects.

But when the mice were exposed to a coronavirus that the vaccine was not designed to protect against, they developed classic symptoms of VAERD. The symptoms included delayed coronavirus clearance and decreased lung function.

This effect, which persisted for at least 10 months, appears to be related to the adjuvant because when alum was replaced with Ribi — an unapproved, research-only adjuvant — mice cleared the virus faster and did not develop VAERD.

Alum’s effect on VAERD was partially reduced by re-immunizing the animals with a Ribi-based adjuvant vaccine.

Ribi adjuvants are emulsions of salt water, a detergent, two bacterial products and the approved adjuvant squalene. Ribi interacts with immune cells to enhance the release of cytokines (immune molecules) and antigen processing.

COVID vaccine-induced VAEDS detected by summer 2020

VAERD is a type of vaccine-associated enhanced disease (VAED) that affects the lower respiratory tract, primarily the lungs. The letter “E” in VAERD and VAED refers to “enhanced” — or atypical cases of a viral disease after vaccination against it.

A 2021 analysis recognized VAED as “a serious barrier to attaining successful virus vaccines.”

Post-vaccination VAERD and related “enhancements” of both infection and respiratory complications have been known since at least the 1960s. Heise cited three examples from prior vaccination campaigns.

In one example, large numbers of breakthrough pediatric measles cases occurred years after vaccination. These were “atypical” in that the children had all measles symptoms, including rash, but the measles virus could not be isolated from them.

In the second example, infants who received the respiratory syncytial virus (RSV) vaccine were later infected by RSV and developed VAERD. Both of these studies were from the 1960s.

The third case, from 2020, involved severe dengue disease outbreaks in dengue-vaccinated children who had previously taken a dengue vaccine.

COVID-19 vaccination-induced VAEDS was already recognized as a complication by the summer of 2020, while the vaccines were still under evaluation. However, a later paper claimed the immunologic changes signifying VAERD were “associated with antiviral protection without disease enhancement” following mRNA-based vaccination.

That is because mRNA COVID-19 vaccines do not use conventional adjuvants. Instead, they rely on “self-adjuventing” from the included genes, their protein expression products or the delivery components (e.g., lipids or fats that carry mRNA into cells).

The immunogenicity of Pfizer’s BNT162b2 mRNA COVID-19 vaccine, for example, results from immune recognition of modified mRNA, the adjuvant properties of lipid nanoparticles and mostly unidentified gene and protein products left over from the vaccine manufacturing process.

Aluminum associated with many ill effects

Adjuvants are chemical irritants that prime the immune system to respond strongly and durably to antigens in vaccines.

Compared with “unadjuvanted” vaccines, vaccines containing an adjuvant are more powerful (thus reducing required doses), enable more rapid immune responses, protect against more antigens and variants, recruit a broader array of immune responses and induce otherwise inaccessible T-cell immune responses.

Although early vaccines — for example, a rabies product used since 1885 and a typhoid vaccine introduced in 1911 — contained irritants that functioned as adjuvants, the formal use of adjuvants as additives did not begin until the 1920s.

Alum, an aluminum-based adjuvant discovered in 1920, has been a mainstay ingredient in vaccines for a century.

Live-attenuated vaccines, such as rotavirus, smallpox and chickenpox, and inactivated-virus vaccines, such as hepatitis A, flu and polio, contain whole viruses, virus fragments and many undefined substances that act as adjuvants.

However, the inactivated-virus COVID-19 vaccines use highly purified antigens so they require extra help to be effective.

That is why alum adjuvants are used in vaccines like hepatitis A, hepatitis B, diphtheria, tetanus, Haemophilus influenzae and pneumococcal disease but not in live viral vaccines, such as measles, mumps, rubella, varicella and rotavirus.

Aluminum, the main ingredient in alum, is associated with many ill effects including injection site inflammation, endocrine disruption, and damage to the digested, cardiovascular and pulmonary systems.

No discussion of the aluminum-containing vaccines

Although mouse study results often do not apply to humans, the authors noted the clinical and immunologic similarities between vaccine-induced illness in mice and VAERD in people.

Both involve type 2 inflammation and the infiltration of immune system cells into the lungs.

Heise’s mouse model was engineered for susceptibility to strong type 2 inflammatory responses, which likely increased their reported immune effects. Mouse models are standard in studies on cancer, HIV infection heart failure and other conditions.

Heise et al. reported that similar vaccine-induced conditions occur in other species and in mice not specifically bred to develop VAERD. Moreover many humans, through either genetics or coronavirus exposure, have developed similar susceptibility.

Because vaccine-induced VAERD occurs after infection with a previously unencountered virus the authors were concerned with novel variants crossing from wild animals to humans, specifically mentioning bats, deer, mink and the “re-emergence of existing SARS-CoV-2 variants from zoonotic [wild animal] reservoirs.”

Yet no evidence links wild animals to COVID-19-causing coronaviruses in the first place.

Because Heise’s study was undertaken to explore connections between alum and VAERD, the absence of any discussion of the aluminum-containing vaccines was surprising. One might assume that each vial or dose contains the same quantities of aluminum but the actual concentrations may vary significantly.

A 2021 study on the aluminum content of 13 common childhood vaccines found that only three contained quantities of alum indicated by the manufacturer. Six had (statistically) significantly more alum and four had less.