(The following is testimony presented to the U.S. Senate Permanent Subcommittee on Investigations on Sept. 9. It has been edited for style and length.)
The scientific evidence supporting vaccine safety and efficacy represents one of the most extensive and transparent bodies of medical research ever assembled. Vaccines have saved an estimated 154 million lives globally over 50 years, eliminated smallpox from the planet and reduced diseases like polio and measles by over 99% in the United States.
Anyone with internet access can read the same studies I read, examine the same data I examine and verify the same conclusions.
Since April 2025, I have co-led the development of a comprehensive public database cataloging 1,704 randomized controlled trials of vaccines spanning from 1941 to 2025, involving more than 10.5 million participants. Multiple independent U.S. surveillance systems continuously monitor vaccine safety in real time, detecting adverse events as rare as 1 per 1 million doses. Recent large-scale studies, including a Danish cohort following 1.2 million children, consistently demonstrate vaccine safety across diverse populations.
The Centers for Disease Control and Prevention estimates that vaccines given to U.S. children born between 1994 and 2023 will prevent approximately 508 million illnesses, 32 million hospitalizations and 1,129,000 deaths over their lifetimes, saving nearly $2.7 trillion in societal costs. This vast evidence base is publicly accessible, peer-reviewed and continuously updated. If vaccines caused a wave of chronic disease, our safety systems — which can detect one-in-a-million events — would have seen it. They haven’t.
I am also part of the Center for Infectious Disease Research and Policy’s Vaccine Integrity Project, where our team is conducting a systematic review and meta-analysis of respiratory virus immunizations from approximately the last two years. This ongoing analysis has examined 590 studies from over 17,000 identified references to date.
As an infectious diseases physician at Stanford University School of Medicine, I have treated many adults with vaccine-preventable diseases throughout my career. These clinical experiences, combined with my research analyzing the extensive evidence base for vaccine safety and efficacy, inform my testimony today.
I should note that I am here in my personal capacity, and the views I share reflect my own professional experience and analysis of the scientific evidence. I have received minimal payments totaling $45.62 over multiple years for food and beverage at work-related events, as documented in the federal Open Payments database. My research time is either self-funded or supported by Stanford University. I testify in my personal capacity as a physician-scientist committed to rigorous evidence and transparent science.
The safety and efficacy data for vaccines is published in peer-reviewed journals, accessible through PubMed, analyzed by independent researchers worldwide, and scrutinized by regulatory agencies whose deliberations are public record. Anyone with internet access can read the same studies I read, examine the same data I examine and verify the same conclusions.
Our international team has built a public database of randomized controlled trials of vaccines. Every entry links directly to its peer-reviewed source publication, allowing anyone to examine the methods, data and results independently. This is how science should work — open, transparent and reproducible.
The transparency of vaccine science extends throughout history. When Edward Jenner published his vaccination findings in 1798, he self-published Variolae Vaccinae for public scrutiny. The 1954 Salk polio vaccine trial involved 1.8 million children in a publicly monitored study, with results announced to the world and data published for examination. This tradition continues today with large-scale epidemiologic studies published in peer-reviewed journals for all to examine.
The United States maintains multiple independent vaccine safety monitoring systems, each operating transparently.
When real risks exist, they are detected, quantified, disclosed and incorporated into guidance. That is how a functioning safety system works.
The Vaccine Adverse Event Reporting System (VAERS) makes every report publicly accessible at vaers.hhs.gov, where anyone can search, download and analyze raw data. The Vaccine Safety Datalink (VSD) covers over 10 million Americans across nine health care organizations, with findings regularly published in peer-reviewed journals and presented at public Advisory Committee meetings. The Post-licensure Rapid Immunization Safety Monitoring (PRISM) system monitors over 190 million people, publishing results openly.
These systems have successfully detected rare adverse events — including intestinal blockage with a rotavirus vaccine in 1999, leading to its withdrawal; rare blood clots with the Johnson & Johnson Covid vaccine (3 per 1 million doses), detected within weeks; and myocarditis signals with mRNA vaccines, promptly investigated and quantified.
When real risks exist, they are detected, quantified, disclosed and incorporated into guidance. That is how a functioning safety system works.
Vaccination has historically united Americans across political lines. George Washington ordered Continental Army variolation against smallpox in 1777, declaring, “I have determined that the troops shall be inoculated.” His orders, preserved in the Library of Congress, reflect understanding that disease threatened his army more than British forces.
Throughout American history, presidents from both parties have championed vaccination as essential public health policy. President Dwight D. Eisenhower signed the Poliomyelitis Vaccination Assistance Act in 1955, stating, “We all hope that the dread disease of poliomyelitis can be eradicated from our society.” President Ronald Reagan proclaimed National Adult Immunization Awareness Week, noting that “vaccination against infectious diseases saves lives and lowers health care costs.” President George H.W. Bush mobilized CDC teams to cities during the 1991 measles resurgence, urging parents: “The vaccines are available. Please, make sure your child is immunized.” Even recently, President Donald Trump acknowledged: “Look, you have vaccines that work — they just pure and simple work. They’re not controversial at all.”
The evidence of vaccine effectiveness is documented in every health department report and mortality database. This data is not hidden — it is published by the CDC and available to anyone.
Before vaccines, measles infected 3-4 million Americans annually, killing approximately 500 children each year. After widespread vaccination led to elimination in 2000, deaths typically numbered zero to two per year. We are currently experiencing our worst outbreak in decades — 1,431 cases through September 2025, with three deaths, overwhelmingly in undervaccinated communities.
Polio paralyzed 16,000 Americans annually in the pre-vaccine era. In 1952 alone, polio caused 57,879 cases and 3,145 deaths, and paralyzed 21,269 Americans. Since 1979, there have been zero cases of wild poliovirus in the United States — a 100% reduction.
Haemophilus influenzae type b (Hib) caused 20,000 cases of severe disease in children under 5 each year, killing approximately 1,000 annually. After vaccine introduction in 1987, cases dropped by over 99%. From 2009 to 2018, only 36 total Hib cases occurred in American children under 5 — across that entire decade.
The transformation is striking: diphtheria killed 13,000-15,000 Americans annually in the early 20th century; in 2024, we had one case. Pertussis killed hundreds of infants yearly; today, typically fewer than 10. Vaccines have saved an estimated 154 million lives globally over 50 years, including 146 million children under 5 years old and 101 million infants. For every death averted, 66 years of full health were gained on average, translating to 10.2 billion years of full health gained. Vaccination has accounted for 40% of the observed decline in global infant mortality — 52% in Africa. In 2024, a child under 10 years old is 40% more likely to survive to their next birthday because of historical vaccination programs.
For respiratory virus vaccines, the primary goal and realistic expectation is to prevent severe disease and death, not infection.
During the 2023-24 influenza season, over 200 children died from flu; among vaccine-eligible children with known vaccination status, more than 80% were not fully vaccinated. Covid-19 vaccines, developed with unprecedented transparency through publicly broadcast Food and Drug Administration and CDC meetings, prevented catastrophic loss of life. A rigorous analysis estimated vaccines prevented 2.5 million deaths globally from 2020 to 2024 (with sensitivity estimates ranging from 1.4-4.0 million). Before vaccines, ICUs were overwhelmed. By mid-2021, nearly every fatal case was among the unvaccinated. During the delta surge, unvaccinated adults were 53 times more likely to die than those vaccinated and boosted.
I cared for hundreds of Covid patients and watched far too many die. I lost many unvaccinated patients across the age spectrum — from their 30s to their 90s — who I am certain would have survived had they been vaccinated. One mother in her 40s without underlying conditions declined vaccination and died, leaving her child behind. These statistics represent preventable human tragedies.
When vaccine safety is studied with robust designs — large, linked databases, matched cohorts, self-controlled methods comparing people to themselves over time — the findings are consistent: no broad increase in chronic diseases among vaccinated people.
Every medical intervention exists on a spectrum of effectiveness. Statins reduce heart attack risk by approximately 30%, not 100%. Cancer chemotherapy may help roughly 40% of patients, not all. We use these treatments because benefits outweigh limitations. Influenza vaccines, used since the 1940s, prevent an estimated 40%-60% of influenza illness in good years, perhaps 20% when the match is poor — yet still prevent thousands of deaths annually.
For respiratory virus vaccines, the primary goal and realistic expectation is to prevent severe disease and death, not infection. While vaccines cannot prevent viruses from initially entering the respiratory tract, they help our immune system recognize the pathogen and mount a rapid response that can prevent infection, transmission or severe disease, depending on the variant and vaccine match. But vaccines excel at keeping people out of the hospital, and for that critical goal, they perform remarkably well.
Our surveillance systems’ transparency was demonstrated during Covid-19 vaccine monitoring. When the possibility of an early myocarditis signal emerged, the CDC issued a Health Alert Network notice on May 27, 2021, urging clinicians to report cases to verify whether a true safety signal existed. Once confirmed through enhanced surveillance, the Advisory Committee on Immunization Practices reviewed data publicly on June 23. The FDA added warnings on June 25. The data showed rates peaked at approximately 106 per million second doses in teenage boys in 2021, mostly mild and short-lived. By 2024-25, rates with updated formulations returned to near background levels, as documented in public ACIP presentations.
Our surveillance systems can detect extremely rare adverse events — as rare as 1 event per 1 million doses or even less. These systems identified thrombosis with thrombocytopenia syndrome (blood clots and low platelets) after the J&J vaccine at a few per million doses overall. The sensitivity of these systems would make any widespread vaccine-related chronic disease impossible to miss.
We take vaccine safety extremely seriously. Vaccines are unique medicines given to large numbers of healthy people. Ensuring their safety through rigorous testing and continuous monitoring is critical.
The evidence for vaccine safety and efficacy exists in overwhelming abundance, accessible to anyone willing to examine it.
My current work exemplifies commitment to openness. Our public database is openly accessible, with search strategies available in the spreadsheets for anyone to examine and verify. The Vaccine Integrity Project team discussed our methods at a public webinar, demonstrating our commitment to transparency even before publication. Every step of our research process is designed to be reproducible and verifiable.
Beyond clinical trials, thousands of additional studies examine vaccine safety through peer-reviewed research. When concerns arise, they are investigated and results are published, whether confirming or refuting initial hypotheses.
The evidence for vaccine safety and efficacy exists in overwhelming abundance, accessible to anyone willing to examine it. From Washington’s orders to inoculate the Continental Army to today’s real-time safety monitoring systems, American vaccination policy has been built on transparency and evidence.
The data supporting vaccines is not hidden — it is reviewed by the FDA, published in peer-reviewed journals, analyzed worldwide and tracked through public surveillance systems. If vaccines caused widespread chronic disease, our safety monitoring systems would have detected it. They haven’t.
The question before this subcommittee is whether public health policy will continue to be guided by transparent, peer-reviewed evidence. As we face both emerging infectious disease threats and the return of old threats due to declining vaccination coverage — like our current measles outbreak — maintaining public confidence through evidence-based communication remains essential.
The data is public. The evidence is clear. I welcome your questions.
