What are the potential harms caused by Severe Acute Respiratory Syndrome (SARS) vaccines?

Potential Harms of SARS Vaccines

SARS vaccines generally have a favorable safety profile, but they may cause neurological adverse effects, exacerbate autoimmune conditions, and lead to immunopathologic responses in some individuals.

Common Adverse Effects

• SARS-CoV-2 vaccines most commonly cause neuropsychiatric, cardiovascular, and musculoskeletal/connective tissue disorders as serious adverse drug reactions (SADRs) 1
• mRNA vaccines (Pfizer-BioNTech/Comirnaty and Moderna/Spikevax) have better safety profiles with lower rates of SADRs (754-785 per million doses) compared to adenovirus-based vector vaccines (1,248-2,301 per million doses) 1
• Moderate, transient reactogenicity (local and systemic reactions) occurs more frequently with mRNA vaccines but is generally not serious 2

Neurological Concerns

• There are theoretical concerns that mRNA-based vaccines may trigger development of de novo neurodegenerative or neurologic disorders, such as demyelinating diseases or fever-induced seizures 3
• Vaccine adjuvants might be responsible for potential neurologic adverse effects 3
• Immunisation stress-related response (ISRR) manifesting as psychogenic non-epileptic seizures (PNES) has been reported 3
• Patients with multiple sclerosis may experience symptom aggravation (pseudo-relapse) following vaccination, although there is a low probability of acute relapse 3

Autoimmune Conditions

• Vaccination against SARS-CoV-2 may exacerbate certain autoimmune conditions by inducing immunological responses and triggering immunological reactions 3
• There have been observational reports of new onset immune-mediated disease and/or disease flares after SARS-CoV-2 vaccination 3
• Specific adverse events reported include cases of uveitis, pericarditis, herpes zoster, and herpes labialis 3
• Thrombocytopenic purpura and myocarditis/pericarditis have been reported after vaccination 3

Immunopathological Concerns

• Animal studies with early SARS coronavirus vaccines showed that while they induced protection against infection, challenged animals exhibited an immunopathologic-type lung disease 4
• In mouse models, SARS-CoV vaccines induced Th2-type immunopathology with prominent eosinophil infiltration upon challenge with live virus, suggesting hypersensitivity to SARS-CoV components 4
• This immunopathological response occurred with multiple vaccine types including inactivated whole virus, virus-like-particle, and recombinant S protein vaccines 4

Special Populations

• Patients on immunosuppressive therapies may have impaired vaccine-induced immune responses, potentially reducing vaccine effectiveness 3
• The effect of corticosteroids on vaccine-induced antibody production is dose-dependent, with higher doses (>10 mg prednisolone daily or equivalent) impairing vaccine response 3
• Patients with autoimmune renal diseases undergoing anti-CD20 therapy (e.g., rituximab) may need to replace their immunosuppressive treatment with another non-interfering regimen until a few weeks after vaccination 3
• Disease-modifying therapies (DMTs) used to treat multiple sclerosis could reduce antibody response following vaccination 3

Risk-Benefit Assessment

• Despite potential adverse effects, the risk of SADRs to any SARS-CoV-2 vaccine appears to be outweighed by the benefits of active immunization against the virus 1
• Serious adverse events in clinical trials were rare, with similar incidence between vaccine and placebo groups 2
• The European Alliance of Associations for Rheumatology (EULAR) supports vaccination for patients with rheumatic and musculoskeletal diseases, taking a "better safe than sorry approach" 3

Monitoring and Precautions

• Vaccination risks and adverse events must be carefully monitored, especially in populations with neurological disorders 3
• Patients with a history of Guillain-Barré syndrome and autoimmune conditions should receive mRNA Covid-19 vaccines if not contraindicated 3
• For patients on certain immunosuppressive medications, timing of vaccination may need to be adjusted relative to treatment schedules 3
• Long-term monitoring is important as the reporting of SADRs tends to be delayed and occurs over a longer time period 1