--- title: Genetics Played a Role in Blood Clots Linked to COVID-19 Shots description: Rare but deadly blood clots tied to J&J and AstraZeneca's vaccines were caused by an autoimmune reaction that some people are predisposed to, researchers found. canonical: https://time.com/6978677/covid-vaccines-blood-clots-genetics/ author: TIME article:opinion: false article:content_tier: free article:published_time: 2024-05-16T04:15:00.000Z article:modified_time: 2026-02-24T17:37:55.431Z article:section: Health og:title: Genetics Played a Role in Blood Clots Linked to COVID-19 Shots og:description: Rare but deadly blood clots tied to J&J and AstraZeneca's vaccines were caused by an autoimmune reaction that some people are predisposed to, researchers found. og:url: https://time.com/6978677/covid-vaccines-blood-clots-genetics/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt646c597f698ee76b/698a56e20116820283985cc5/covid19-vaccine.jpg?branch=production&width=1024&quality=75&auto=webp&crop=16:9 og:image:width: 1024 og:image:height: 576 og:image:alt: COVID-19 vaccine og:type: article twitter:card: summary_large_image twitter:title: Genetics Played a Role in Blood Clots Linked to COVID-19 Shots twitter:description: Rare but deadly blood clots tied to J&J and AstraZeneca's vaccines were caused by an autoimmune reaction that some people are predisposed to, researchers found. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt646c597f698ee76b/698a56e20116820283985cc5/covid19-vaccine.jpg?branch=production&width=1024&quality=75&auto=webp&crop=16:9 ---  # Genetics Played Role in Rare Blood Clots Linked to COVID-19 Vaccines, Researchers Find > Sponsored content. 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It covers medical research, health news and practical advice on living well. #### Where can I get reliable health news by email? Health Matters is TIME's weekday health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free weekday newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-health-2026q3/newsletters?i=1c0f6dcf-0da3-4b1a-baa8-d45a7ddac836&cr=time-nl-health-2026q3-v1) by [Jason Gale / Bloomberg](https://time.com/author/bloomberg/) ## Jason Gale / Bloomberg Contributor May 16, 2024 4:15 AM UTC  A health worker administers a dose of the Janssen COVID-19 vaccine to a homeless person during a vaccination campaign in Bangladesh. A health worker administers a dose of the Janssen COVID-19 vaccine to a homeless person during a vaccination campaign in Bangladesh. Sazzad Hossain—SOPA/LightRocket/Getty Images by [Jason Gale / Bloomberg](https://time.com/author/bloomberg/) ## Jason Gale / Bloomberg Contributor May 16, 2024 4:15 AM UTC Rare but deadly blood clots tied to Johnson & Johnson and AstraZeneca Plc’s Covid-19 shots were caused by an autoimmune reaction that some people are predisposed to, researchers found, a discovery that they say will shape development of future vaccines. Adenovirus-based vaccines, like the J&J and AstraZeneca shots that were later pulled from the market, contain a component that, in genetically susceptible people, can trigger the production of unusually structured antibodies against a protein involved in blood clotting, scientists said Wednesday in a letter to the New England Journal of Medicine. Researchers plan to identify the culprit and then try to remove it using genetic engineering. **Read More:** [_How COVID-19 Vaccines and Infections Are Tweaking Our Immunity_](https://time.com/6564464/covid-19-changing-immune-system/) An extremely similar deleterious antibody response occurs in susceptible patients after infection with [adenoviruses](https://www.cdc.gov/adenovirus/symptoms.html), which often infect the airways and lead to cold-like symptoms, the study found. It’s not known how many people may be susceptible to the complication, said Tom Gordon, head of immunology at Flinders University in South Australia, whose molecular sleuthing led to the [finding](https://www.nejm.org/doi/full/10.1056/NEJMc2402592). The immune reaction linked to the shot is “a new disease,” he said in an interview. Hematologists and intensive care specialists are likely to spot more cases as they become familiar with it, he said. “It’s a kind of autoimmunity where we know the trigger,” said immunologist James McCluskey, assistant vice chancellor of the University of Melbourne, who wasn’t involved in the research. “That’s unusual. In most cases we never get a handle on the trigger.” ## **Vaccines withdrawn** Out of more than 18 million people who received the single-dose J&J vaccine, [60 cases](https://www.yalemedicine.org/news/coronavirus-vaccine-blood-clots) of the clotting disorder were reported and nine people died, according to the Yale School of Medicine. A small number of clot-related deaths tied to the AstraZeneca vaccine led to its withdrawal or restriction in Denmark, Norway and other countries in 2021\. The complication occurred in [about 2-3 people](https://www.health.gov.au/our-work/covid-19-vaccines/advice-for-providers/clinical-guidance/tts#:~:text=There%20was%20a%20link%20between,aged%2060%20years%20or%20older) per 100,000 vaccinated with the Astra shot under age 60 in Australia, where it hasn’t been available since March 2023\. The European Commission [withdrew](https://www.ema.europa.eu/en/medicines/human/EPAR/vaxzevria-previously-covid-19-vaccine-astrazeneca) the marketing authorization for the immunization in March 2024. “AstraZeneca welcomes any further examination of the possible underlying mechanism of thrombosis with thrombocytopenia syndrome (TTS), given that, despite extensive investigation, we do not yet understand the mechanism that can in very rare cases be a trigger for TTS,” a spokesperson for the company said. J&J also said it supports research that helps guide development of safe and effective vaccines. **Read More:** [_The Miracle Workers: Vaccine Scientists Are TIME’s 2021 Heroes of the Year_](https://time.com/heroes-of-the-year-2021-vaccine-scientists/) “More data are needed to fully understand potential factors that may be associated with this rare event, including its potential relationship with adeno- and other viruses, to draw appropriate conclusions about the underlying pathogenesis,” the company said in an email. Both shots played an important role in vaccine programs during the early stages of the pandemic. One analysis found the Astra vaccine saved an estimated [6.3 million](https://www.airfinity.com/articles/astrazeneca-and-pfizer-biontech-saved-over-12-million-lives-in-the-first) lives in 2021. The [mRNA vaccines](https://time.com/5927342/mrna-covid-vaccine/) made by the Pfizer Inc.-BioNTech SE partnership and Moderna Inc. were later found to be more effective at protecting against Covid and have been updated to tackle more recent virus variants. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/6978677/covid-vaccines-blood-clots-genetics/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/6978677/covid-vaccines-blood-clots-genetics/"},"headline":"Genetics Played Role in Rare Blood Clots Linked to COVID-19 Vaccines, Researchers Find","datePublished":"2024-05-16T04:15:00.000Z","dateModified":"2026-02-24T17:37:55.431Z","description":"Rare but deadly blood clots tied to J&J and AstraZeneca's vaccines were caused by an autoimmune reaction that some people are predisposed to, researchers found.","url":"https://time.com/6978677/covid-vaccines-blood-clots-genetics/","keywords":["COVID-19","wire","overnight","News Desk"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt646c597f698ee76b/698a56e20116820283985cc5/covid19-vaccine.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Jason Gale / Bloomberg"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt646c597f698ee76b/698a56e20116820283985cc5/covid19-vaccine.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"COVID-19 vaccine","caption":"A health worker administers a dose of Janssen COVID-19 vaccine to a homeless person during a vaccination campaign for transgender community and homeless people in Central Shaheed Minar, Dhaka, Bangladesh.","creditText":"Sazzad Hossain—SOPA/LightRocket/Getty Images","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/covid-19/","name":"COVID-19"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/6978677/covid-vaccines-blood-clots-genetics/","name":"Genetics Played Role in Rare Blood Clots Linked to COVID-19 Vaccines, Researchers Find"}}]}] ```