Over de mRNA-vaccins tegen COVID-19 wordt doorgaans gediscussieerd alsof er maar één ding te zeggen was, terwijl er meerdere aspecten zijn; deze pagina stelt elk van die aspecten voor met het gewicht dat het bewijs ondersteunt. In twee grote placebo-gecontroleerde trials waren ze ongeveer 95% effectief tegen symptomatische COVID-19, en tijdens de vroege landelijke uitrol verminderden ze hospitalisaties en sterfte met circa 97% bij ouderen en mensen met een verhoogd risico. Bescherming tegen het oplopen van het virus en het doorgeven ervan was aanvankelijk aanwezig, maar nam binnen enkele maanden af; daarom hield de boodschap uit 2021 dat vaccinatie betrouwbare overdracht zou voorkomen niet stand.
De vaccins gaan ook gepaard met specifieke risico's: myocarditis, geconcentreerd bij jonge mannen en het hoogst na de tweede dosis, meestal mild; zeldzame anafylaxie; en een heranalyse van de eigen trials van de fabrikanten die ongeveer 1 op de 800 extra ernstige bijwerkingen aantoonde. Twee veel gedeelde alarmberichten — namelijk dat het spike-eiwit van het vaccin in de hersenen doordringt en schade veroorzaakt, en dat lijkbezorgers een nieuw, door het vaccin veroorzaakt bloedstolsel vinden — zijn niet bevestigd; deze pagina toont precies hoe tot die conclusie wordt gekomen. Dit is educatie over het bewijs, geen medisch advies noch een aanbeveling voor of tegen.
Findings & Outcomes
What an mRNA Vaccine Is
An mRNA vaccine is a strand of messenger RNA wrapped in a protective lipid nanoparticle. It carries a set of instructions, not a piece of the virus. Those instructions tell a person's own cells to make one part of SARS-CoV-2, the spike protein. The mRNA is short-lived. The body breaks it down within days, and it never enters the cell nucleus or alters DNA. The approach grew out of about 20 years of research before the pandemic.
What the Trials Found
The Pfizer-BioNTech trial enrolled about 43,000 people. Eight cases of COVID-19 appeared in the vaccine group against 162 in the placebo group, a 95.0% efficacy against symptomatic disease from the original virus (Polack 2020). The Moderna trial enrolled about 30,000 people. Eleven cases appeared in the vaccine group against 185 in placebo, a 94.1% efficacy.
When the vaccines reached the whole of Israel in early 2021, two doses cut hospitalization by about 97%. They cut severe or critical disease by 97.5% and death by 96.7% in that early period. The benefit fell most heavily on older and higher-risk people.
Protection against catching the virus did not last. Against symptomatic Omicron, two doses were about 65.5% effective at 2 to 4 weeks, then dropped below 10% by around 25 weeks (Andrews 2022). A booster restored protection to about two thirds before it too declined. The 2021 message that vaccination would reliably stop transmission did not hold.
Immunity from a prior infection is real. It gave about 74.6% protection against hospitalization or severe disease at one year, though protection against catching the virus again waned to around 24.7%. Hybrid immunity, infection plus vaccination, proved the most durable, at about 97.4% against severe disease over a year.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
How it works
mRNA vertelt je cellen om de spike te maken en wordt daarna binnen enkele dagen afgebroken zonder het DNA te veranderen
Het vaccin is een set instructies, geen stukje van het virus. Het vertelt je cellen om één onderdeel van het virus te maken, de spike, zodat je immuunsysteem dit vooraf leert herkennen. De instructies zijn kortstondig en veranderen je DNA niet.
De messenger-RNA-vaccintechnologie werd gedurende ongeveer twee decennia voor de pandemie ontwikkeld. Een streng mRNA die codeert voor het spike-eiwit van SARS-CoV-2 wordt ingekapseld in een lipide-nanodeeltje dat het beschermt en helpt het cellen binnen te dringen. Ribosomen in het cytoplasma vertalen het mRNA naar spike-eiwit, dat aan het immuunsysteem wordt getoond, wat antilichaam- en T-celreacties opwekt. Het mRNA werkt in het cytoplasma, wordt in dit platform niet omgezet in DNA en teruggeschreven in het genoom, en wordt binnen enkele dagen afgebroken door normale cellulaire processen. Pardi en collega's bespreken het platform, de geschiedenis ervan en de immunologie.
The study · 1
Pardi et al., mRNA vaccines: a new era in vaccinology · Nat Rev Drug Discov 2018;17(4):261-279
Vaccine spike antigen shows up within a day and clears as antibodies rise
The spike protein the vaccine makes does not stick around. In a small study, it showed up in the blood within a day and then cleared as the body built antibodies. This argues against the idea that vaccine spike lingers and circulates for a long time.
Ogata and colleagues measured SARS-CoV-2 proteins in longitudinal plasma samples from 13 recipients of two doses of mRNA-1273. Eleven of 13 had detectable SARS-CoV-2 antigen as early as day 1 after the first injection, and clearance of detectable antigen correlated with the production of IgG and IgA. The study is small and measures antigen presence and kinetics, not any clinical outcome, but it is direct human evidence that vaccine-produced spike antigen is transient. It is given no direction because it is a biodistribution finding, not a benefit or a harm.
The study · 1
Ogata et al., circulating SARS-CoV-2 vaccine antigen detected in the plasma of mRNA-1273 recipients · Clin Infect Dis 2022;74(4):715-718
Spike crossing the blood-brain barrier is shown in mice, not in vaccinated people
The worry that the vaccine spike gets into the brain and causes damage is not established in humans. The study behind it used the virus's spike protein injected into mice, showing it can cross into a mouse brain. That is about the virus in an animal, not about vaccination causing brain harm in people.
Rhea and colleagues showed that radioiodinated S1, the S1 subunit of the SARS-CoV-2 spike protein, injected intravenously into mice, readily crossed the blood-brain barrier and entered brain tissue, and was also taken up by lung, spleen, kidney and liver. This is legitimate mechanistic work about the virus's protein in a mouse model. It does not measure vaccination, it does not measure humans, and it does not establish a clinical neurological injury from vaccination. It is graded preliminary and given no direction because it neither demonstrates harm from vaccination nor rules it out.
The study · 1
Rhea et al., the S1 protein of SARS-CoV-2 crosses the blood-brain barrier in mice · Nat Neurosci 2021;24(3):368-378
Respiratory Infection
Ongeveer 95% effectief tegen symptomatisch COVID-19 in de cruciale onderzoeken
In de grote onderzoeken verlaagden de vaccins de kans om ziek te worden van COVID-19 door het oorspronkelijke virus met ongeveer 95%. Dit waren grote, placebogecontroleerde studies met elk tienduizenden deelnemers.
Polack en collega's randomiseerden ongeveer 43,548 deelnemers naar twee doses BNT162b2 of placebo en rapporteerden 95.0% effectiviteit tegen symptomatisch, PCR-bevestigd COVID-19 (95% BI 90.3 tot 97.6), met 8 gevallen in de vaccingroep tegenover 162 in de placebogroep. Baden en collega's randomiseerden ongeveer 30,420 deelnemers naar mRNA-1273 of placebo en rapporteerden 94.1% effectiviteit (95% BI 89.3 tot 96.8), met 11 tegenover 185 gevallen. Beide onderzoeken maten een vooraf gespecificeerde harde uitkomst tegen de oorspronkelijke stam over een periode van weken tot enkele maanden; geen van beide kon de duurzaamheid op lange termijn of de bescherming tegen nog niet ontstane varianten meten.
The studies · 2
Polack et al., safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine · N Engl J Med 2020;383(27):2603-2615
Baden et al., efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine · N Engl J Med 2021;384(5):403-416
Ongeveer 97% minder ziekenhuisopname en overlijden tijdens de vroege uitrol in Israël
Toen het vaccin in een vroeg stadium in een heel land werd uitgerold, hadden volledig gevaccineerde mensen een veel kleinere kans om gehospitaliseerd te worden of te overlijden aan COVID-19, met ongeveer 97%. Deze bescherming tegen ernstige ziekte is het sterkste deel van het pleidooi voor de vaccins.
Haas en collega's gebruikten landelijke surveillancegegevens van het Israëlische ministerie van Volksgezondheid over de eerste vier maanden van de BNT162b2-campagne. Zeven dagen of langer na de tweede dosis waren de effectiviteitsschattingen 95.3% tegen infectie, 97.0% tegen symptomatisch COVID-19, 97.2% tegen ziekenhuisopname, 97.5% tegen ernstige of kritieke ziekenhuisopname en 96.7% tegen overlijden. Het voordeel was het grootst bij oudere en hoogrisicogroepen, die het grootste deel van de last van ernstige ziekte dragen. Dit is een observationele, praktijkgerichte schatting uit een periode die werd gedomineerd door de Alpha-variant, geen gerandomiseerd onderzoek.
The study · 1
Haas et al., impact and effectiveness of BNT162b2 following a nationwide campaign in Israel · Lancet 2021;397(10287):1819-1829
Bescherming tegen infectie daalde van ongeveer 65% tot onder de 10% na 25 weken
De vaccins verminderden aanvankelijk infectie, maar die bescherming nam binnen enkele maanden af en daalde sterk zodra Omicron opdook. De vroege boodschap dat vaccinatie betrouwbaar zou voorkomen dat je het virus opliep of verspreidde, hield op de lange termijn geen stand.
Andrews en collega's gebruikten een test-negatief case-control-ontwerp in Engeland om de effectiviteit tegen symptomatische ziekte door de Omicron-variant te schatten. Na twee doses BNT162b2 was de effectiviteit tegen symptomatische Omicron ongeveer 65.5% na 2 tot 4 weken, afnemend tot onder de 10% na 25 weken of langer. Een boosterprik verhoogde dit tot ongeveer 67% na 2 tot 4 weken, wat vervolgens in de daaropvolgende weken weer afnam. De effectiviteit tegen ernstige uitkomsten hield aanzienlijk beter stand dan tegen symptomatische infectie. De bevinding hier gaat specifiek over de duurzame preventie van infectie en transmissie, die niet werd bereikt, in tegenstelling tot de bescherming tegen ernstige ziekte.
The study · 1
Andrews et al., Covid-19 vaccine effectiveness against the Omicron variant · N Engl J Med 2022;386(16):1532-1546
Eerdere infectie ongeveer 74.6% tegen ernstige ziekte; hybride immuniteit het meest duurzaam met 97.4%
Immuniteit door het doormaken van COVID is reëel en aanzienlijk, vooral tegen ernstige ziekte, en houdt redelijk goed stand. Bescherming tegen herinfectie neemt sneller af. De sterkste, meest duurzame bescherming ontstond uit een combinatie van zowel infectie als vaccinatie.
Bobrovitz en collega's voerden een systematische review en meta-analyse uit van studies naar bescherming door eerdere SARS-CoV-2-infectie en door hybride immuniteit, grotendeels tegen de Omicron-variant. Eerdere infectie alleen bood na 12 maanden ongeveer 74.6% bescherming tegen ziekenhuisopname of ernstige ziekte en 24.7% tegen herinfectie na 12 maanden. Hybride immuniteit bood na 12 maanden ongeveer 97.4% bescherming tegen ernstige ziekte. Dit is opgenomen omdat de sterkte van door infectie verworven immuniteit relevant was voor het vertrouwensverhaal, waarbij de rol ervan in publieke communicatie kritiek opriep.
The study · 1
Bobrovitz et al., protective effectiveness of previous infection and hybrid immunity against Omicron and severe disease · Lancet Infect Dis 2023;23(5):556-567
Evidence And Methods
VAERS captures fewer than 1% of adverse events, so counts are a floor
VAERS is a passive system that relies on someone noticing an event and filing a report, so it misses most of what happens. An AHRQ-funded project estimated that fewer than 1% of vaccine adverse events are reported to it, which means the raw counts are a floor, not the true number.
The ESP:VAERS project (Lazarus, Klompas and colleagues, AHRQ Grant Final Report R18 HS 017045, Harvard Pilgrim Health Care, 2010) built an automated electronic system to detect and report vaccine adverse events across a large patient population. The report states that fewer than 1% of vaccine adverse events are reported to VAERS, framing the passive system's low sensitivity as the problem the automated tool was meant to solve. The specific fewer-than-1% figure is an estimate and the automated system was not ultimately adopted for routine use. What is well established, and what this row carries, is directional: passive spontaneous-reporting systems substantially undercount adverse events, so raw VAERS totals are a floor, not a full census. This row is given no direction because it describes a measurement limitation, not a benefit or a harm.
The study · 1
Lazarus, Klompas et al., electronic support for public health, vaccine adverse event reporting system (ESP:VAERS), AHRQ Grant Final Report R18 HS 017045 · Agency for Healthcare Research and Quality, 2010
Myocarditis in Young Men
Myocarditis, inflammation of the heart muscle, sits at the top of the documented harms, acknowledged by regulators including the CDC and FDA. It concentrates in young males and peaks after the second dose, somewhat more often after Moderna than Pfizer-BioNTech. US surveillance confirmed 1,626 cases at a median age of 21, most of them male. Reporting rates ran highest in males 16 to 17, at about 105.9 per million second doses of the Pfizer-BioNTech vaccine (Oster 2022).
Israeli active surveillance put the risk in young men at several times the expected background rate. A Nordic cohort of about 23 million residents of Denmark, Finland, Norway and Sweden placed the excess squarely in young men after a second Moderna or Pfizer-BioNTech dose. It ran higher after Moderna. In October 2021, before that evidence was in, Sweden, Denmark, Finland and Norway paused or restricted the Moderna vaccine for younger age groups.
The reassuring part is real. The great majority of cases were mild and resolved, and most patients under 30 went home after a short admission.
The Global Vaccine Data Network followed about 99 million vaccinated people across eight countries. It confirmed the myocarditis and pericarditis signals after mRNA vaccines, and flagged a rare inflammatory brain condition, acute disseminated encephalomyelitis, after a first Moderna dose. The same study's signals for Guillain-Barre syndrome and cerebral venous sinus thrombosis followed the ChAdOx1 adenovirus-vector vaccine, a different technology and not an mRNA product.
Anaphylaxis stays rare and treatable. One careful study put it on the order of a few per 10,000 vaccinations, with the affected people recovering.
The Excess of Serious Adverse Events in the Trials
Fraiman and colleagues, writing in Vaccine in 2022, pooled the serious adverse events that manufacturers had prespecified as events of special interest, drawn from their own randomized trial data. That watch-list showed an excess of about 12.5 per 10,000, roughly 1 in 800 (95% CI 2.1 to 22.9, risk ratio 1.43). Put plainly, about 12 to 13 more people per 10,000 vaccinated had a serious event of that kind than in placebo. The authors called for formal harm-benefit analyses tied to a person's actual risk of severe COVID-19, not one figure for everyone.
What Passive Reporting Can and Cannot Tell You
VAERS works passively: someone must notice an event, connect it to the vaccine, and file a report. An analysis funded by the Agency for Healthcare Research and Quality, run at Harvard Pilgrim Health Care, estimated that fewer than 1% of vaccine adverse events reach VAERS. Raw counts are therefore only a floor. The under-reporting factor is uncertain and shifts with how serious and how recognizable an event is. Multiplying a count by 100 and calling the result a fact is not supported.
The Spike-in-the-Brain Claim
The claim that the vaccine's spike protein crosses into the brain and does harm is not established in people. The research behind it is mechanistic and mostly about the virus. Purified viral spike protein injected into mice can cross the mouse blood-brain barrier, an animal model that does not show vaccination injuring a human brain. On the vaccine side, a small study of people given an mRNA vaccine found spike antigen in the blood within about 24 hours. It then cleared as antibodies rose, arguing against the vaccine spike lingering for long periods.
The Embalmer-Clot Claim
Some embalmers, one of them public since 2021, report finding unusual large white fibrous clots and attribute them to vaccination. The 2022 film Died Suddenly amplified the idea and drew wide criticism for its footage and data. No peer-reviewed study has established a new clot phenomenon or tied one to vaccination at population scale. Pale, fibrin-rich clots that form after death, long called chicken-fat clots, are a well-documented normal finding in forensic pathology, described before the pandemic and reviewed systematically since. The reports remain uninvestigated anecdotes with no denominator and no comparison group.
An observation that has not been systematically studied is not the same as one a study has ruled out.
Reading the Evidence With the Incentives in View
Two companion pages bear on how this story was handled: COVID-19 treatments and how industry shapes science. Remdesivir became a patented, expensive standard of care on trial evidence that did not support a survival benefit, and the WHO recommended against it weeks later. A cheaper generic was dismissed before its own trials were run. What becomes standard, and what gets the benefit of the doubt, tracks incentives as much as outcomes.
Guidance shifted on masks and transmission through 2020 and 2021, mandates were introduced, and prior-infection immunity and the lab-leak possibility were marginalized early, then treated as more plausible later. A question being called settled was not the same as its being settled.
Go Deeper
- Ivermectin: the pandemic's other contested drug, promoted as a miracle and dismissed as a veterinary product, and a model for holding both directions of a story at once.
- Expectancy and belief: how conviction and a compelling narrative shape what people feel a treatment did, on all sides of a debate.
- The biology of aging: another field where solid science sits alongside claims that outrun the evidence.
Common Questions
Does the vaccine contain the virus, and can it give me COVID-19?
No. It carries instructions for a single viral protein, not the virus, so nothing in it can reproduce or start an infection. Your immune system learns to recognize that one protein before the real virus, the thing that causes COVID-19, ever arrives.
How do I weigh the myocarditis risk against the risk from COVID-19 itself?
It depends on the person. A healthy young man and an older, higher-risk adult face very different balances of harm and benefit. That is the balance Fraiman's reanalysis pointed to, arguing the calculation be made per person rather than as a single number.
The vaccine arrived fast, so was the science rushed?
The mRNA delivery platform was not invented in 2020; it grew out of research stretching back well before the pandemic. What moved quickly that year was large-scale testing and manufacturing, run in parallel instead of one stage after another. Those trials still enrolled tens of thousands of people before the authorizations at the end of 2020.
Documented Harms and Contested Safety Claims
Everything to be aware of is here, in one place. This practice suits most healthy people; a few situations call for real care.
Myocarditis in young men after the second dose, about 105.9 per million in males 16 to 17
Oster and colleagues reviewed reports to the US Vaccine Adverse Event Reporting System, confirming 1,626 myocarditis cases among people over 12 (median age 21, median onset 2 days, 82% male among cases with sex reported). Crude reporting rates within 7 days exceeded expected rates in multiple young age and sex strata, highest in males 16 to 17 (about 105.9 per million second BNT162b2 doses) and 12 to 15 (about 70.7 per million). About 96% of confirmed cases were hospitalized, and about 87% of those hospitalized had resolution of symptoms by discharge. Mevorach and colleagues, in Israeli active surveillance, found a standardized incidence ratio of 5.34 (95% CI 4.48 to 6.40) overall after the second dose, highest in males aged 16 to 19 (rate ratio about 8.96), with a clinical course that was generally mild. Regulators including the CDC and FDA acknowledge the signal.Oster et al., myocarditis cases reported after mRNA-based COVID-19 vaccination in the USMevorach et al., myocarditis after BNT162b2 mRNA vaccine against Covid-19 in IsraelKarlstad et al., SARS-CoV-2 vaccination and myocarditis in a Nordic cohort study of 23 million residents
A study of 99 million confirmed the myocarditis and pericarditis signals
Faksova and colleagues, in the Global Vaccine Data Network cohort, analyzed adverse events of special interest up to 42 days after vaccination across 99,068,901 people and 23.2 million person-years, using observed-versus-expected ratios. The analysis confirmed pre-established signals for myocarditis and pericarditis after mRNA vaccines and flagged acute disseminated encephalomyelitis after a first mRNA-1273 dose (observed-to-expected ratio 3.78). The Guillain-Barré and cerebral venous sinus thrombosis signals it reported followed the ChAdOx1 adenovirus-vector vaccine, not the mRNA vaccines. Signals with a lower confidence bound above 1.5 were treated as warranting further investigation.Faksova et al., COVID-19 vaccines and adverse events of special interest: a Global Vaccine Data Network cohort of 99 million
Anaphylaxis is rare and treatable, about 2.5 per 10,000 vaccinations
Blumenthal and colleagues examined acute allergic reactions to mRNA COVID-19 vaccines among 64,900 employees in a Massachusetts health-care system. Acute allergic reactions were self-reported in about 2.1% of vaccinations, and 16 cases met criteria for anaphylaxis, roughly 2.47 per 10,000, all of whom recovered. This single-system rate is higher than the few-per-million figures from national passive surveillance, a difference typical of active versus passive monitoring, but both agree the event is rare and manageable.Blumenthal et al., acute allergic reactions to mRNA COVID-19 vaccines
A reanalysis of the trials found about 1 in 800 excess serious adverse events
Fraiman and colleagues reanalyzed serious adverse events of special interest (a Brighton Collaboration priority list) from the phase III randomized trials of the Pfizer-BioNTech and Moderna mRNA vaccines. Across both, the excess risk of serious adverse events of special interest was 10.1 per 10,000 for Pfizer-BioNTech and 15.1 per 10,000 for Moderna, combined 12.5 per 10,000 (95% CI 2.1 to 22.9), a risk ratio of 1.43 (95% CI 1.07 to 1.92). The authors noted the confidence intervals are wide and the analysis is a secondary reanalysis of trial data with its own limits, and called for formal harm-benefit analyzes stratified by an individual's risk of severe COVID-19, not a single population figure. This is graded moderate: it rests on randomized-trial data, but as a post-hoc pooled reanalysis with wide intervals it is a signal to weigh, not a settled effect size.Fraiman et al., serious adverse events of special interest following mRNA COVID-19 vaccination in randomized trials in adults
The embalmer clot reports are anecdotes, not a studied new phenomenon
The claim traces to embalmer reports circulating since 2021 and the 2022 film Died Suddenly, which was widely criticized for how it presented footage and data. A search of the peer-reviewed literature finds no systematic investigation establishing a new clot phenomenon or a vaccine link at population scale. By contrast, pale, fibrin-rich clots forming after death, described as chicken-fat clots, are a recognized entity in forensic pathology: medico-legal case studies characterized them well before the pandemic (2008), and a 2025 systematic review of cadaver clots catalogues the antemortem, agonal and postmortem categories while noting that comparative science distinguishing them remains incomplete. The most parsimonious reading is that the embalmer observations describe a mundane, long-known postmortem process. The reports are uncontrolled anecdotes with no denominator, so they establish neither harm nor its absence.Solarino et al., cadaver clots: a systematic review of the literatureUekita et al., medico-legal investigation of chicken-fat clot in forensic cases
The safety findings are gathered here so the rest of the page can read plainly.
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 17 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 10, 2026.
Evidence strength
How confidently the research supports a claim. Strength describes the evidence, not our endorsement.