Vaccine enhanced disease (VED)

Immune enhancement response describes a situation where the person vaccinated against a disease becomes ill immediately following vaccination.  It is not understood whether this is because of contaminants in the vaccine (including contamination by residues of non-target organisms), or effects of prior vaccines given to the individual ("cross-reaction") or an unintended stimulation of the immune system (such as re-activation of a "silent" retrovirus in the individual) or by some other mechanism or combination of effects.  Official government agencies which regulate, authorize and promote vaccines have made little attempt to clarify such issues.  In part, this unwillingness has raised a distrust of vaccination.

Paradoxical immune enhancement (aka pathological priming, antibody dependent enhancement (ADE) and several other names) is a term used when a vaccine enhances susceptibility to severe illness and death, which expresses when the person is subsequently infected with the actual disease-causing virus.  In other words, the disease is enhanced by the prior vaccination. It has something to do with the stimulation of "binding antibodies", as opposed to "neutralizing antibodies". This "as yet unexplained" phenomenon, also known as vaccine enhanced disease (VED), produces an immune system overreaction -- a "cytokine storm" --  when the test subjects (in past trials both children or animals) that previously responded well to the vaccination were then exposed to the wild version of the virus.

Cell-based enhancement is a different category of paradoxical immune enhancement in which the vaccine-primed immune system launches a shoddy response to a subsequent natural infection caused by Th2 immunopathology: a faulty T cell response triggers allergic inflammation and poorly functional antibodies that form immune complexes, activating the complement system and potentially damaging the airways. In some cases, the enhancement processes might overlap. Th2 immunopathology is less well studied and may be more serious in the case of vaccine injury by vaccinations for SARS Cov-2, especially among the elderly.

Since the 1960s, tests of vaccine candidates for diseases such as dengue, respiratory syncytial virus (RSV) and severe acute respiratory syndrome (SARS) have shown a paradoxical phenomenon: Some animals or people who received the vaccine and were later exposed to the virus developed more severe disease than those who had not been vaccinated.  In animal studies of SARS, aged mice were found to have particularly high risks of life-threatening Th2 immunopathology.

Clinical trials in 2014 of the dengue fever vaccine Dengvaxia elicited a very positive, favourable, antibody response in several hundred thousand children in the Philippines.  On this basis, the vaccine was affirmed as part of a national campaign to eliminate dengue.  However, when the vaccinated children subsequently actually contracted dengue, many got very sick and 600 died. The vaccine manufacturer, Sanofi, disclosed in 2017 that it was aware that the vaccine could cause more serious cases if given to patients without a prior dengue infection, at which point the Filipino government cancelled the campaign, sought a refund of costs from the vaccine manufacturer and is prosecuting criminally the local agencies and individuals involved in the decision-making.