I will never forget the pain of my colposcopy.
I was in my early twenties. A routine pap smear had come back with what the doctor called "abnormal cells." HPV. Human papillomavirus. The next step was for a gynecologist to take a hole puncher to my cervix and send the tissue off to find out whether I had cancer.
The pain was searing. I went into a vasovagal tailspin on the table. They handed me a pad, told me what to expect over the next few days, and sent me home to my grad school apartment to wait.
A few days later, the result came back: pre-cancerous. A sigh of relief, sort of.
Of course, what I went through was nothing compared to the pain of someone hearing, "You have cancer." My experience was a scare; the thing the HPV vaccine prevents is not a scare.
How could the HPV vaccine be controversial?
Rewind to my teenage years: There was no HPV vaccine. By the time it did become available, I was 20, already sexually active, and had no idea I was a candidate. If I had a time machine, I would go back and get it without hesitation. While I don’t have a time machine, I do have a son scheduled for his first dose at his upcoming well visit, and a daughter who will be eligible next year. That is how I get to reap the benefits of this vaccine now.
I will never understand how the HPV vaccine, a cancer prevention tool, became controversial. We have a way to prevent the big C. The big C. The thing every family I know fears. We have a vaccine that prevents it, and one of the biggest fumbles in modern public health was not branding it that way from the start. Not as a shot for a sexually transmitted infection. As a cancer vaccine. Because that is what it is.
Australia figured this out early. Officials there began universal HPV vaccination in 2007, achieved some of the highest coverage rates in the world, and are now on track to be the first country to eliminate cervical cancer as a public health problem by 2035. Cervical cancer incidence there is already among the lowest globally. That is what high uptake of this vaccine looks like at the population level: disappearing cancer.
In the United States, we are moving in the opposite direction.
In January, the Department of Health and Human Services (HHS) changed the childhood immunization schedule. While the HPV vaccine remained on the schedule, its recommendation changed from a two-dose schedule to a single dose between ages 11 and 12. Unlike some other changes to the childhood immunization schedule, the shift to one dose had international precedent. Preliminary evidence suggests that one dose may provide comparable protection against certain key cervical outcomes in females. Globally, several other countries have shifted to the one-dose schedule already. The shift is justifiable on financial and programmatic grounds: lower vaccine costs, simpler delivery, and the ability to reach more girls with limited vaccine supply.
That is what high uptake of this vaccine looks like at the population level: disappearing cancer.
However, the reasons those countries shifted are not the reasons HHS cited, and the context is different. Significant gaps remain in the evidence base that informs US HPV vaccine policy, particularly regarding non-cervical cancers, effectiveness in males, and the long-term durability of single-dose protection.
None of those gaps were addressed before the schedule change was made. HHS pointed to what other "comparable" countries were doing, but the comparison does not hold. Countries that have driven cervical cancer incidence down through nearly two decades of high two-dose coverage are in a different position than the United States, where uptake is uneven and HPV-associated cancer rates remain substantial. The shift was made without an updated evidence review, an ACIP discussion, or anything resembling the standard process. A federal judge in March struck the change down on procedural grounds.
The American Academy of Pediatrics has held the line on two doses until the evidence supports a change. That is what professional medical bodies are for.
Sound data from new evidence review
And this is where the Vaccine Integrity Project (VIP) at the Center for Infectious Disease Research and Policy (CIDRAP) comes in. VIP does not make clinical recommendations. Its researchers synthesize the evidence so the recommending bodies can work from a rigorous foundation. The VIP’s new systematic review and meta-analysis on HPV vaccine safety, effectiveness, and immunogenicity was recently released, and it tells the story you would expect after two decades of post-licensure surveillance.
The headline on safety is reassuring. Across 274 studies, there is no credible evidence linking HPV vaccination to serious adverse events, Guillain-Barré syndrome, chronic fatigue syndrome, complex regional pain syndrome, infertility, premature ovarian failure, paralysis, or adverse pregnancy outcomes. Two small recent studies suggested a possible association with postural orthostatic tachycardia syndrome (POTS), a condition affecting heart rate and blood flow, but the larger body of evidence does not support a link.
The headline on effectiveness is that this vaccine works extraordinarily well. Vaccinated girls and women have a 66% lower risk of invasive cervical cancer and an 80% lower risk when vaccination starts at or before age 16. Randomized trials show an 84% to 90% reduction in persistent infection with HPV-16 and HPV-18, the two strains responsible for most cervical cancers. There is strong protection against the high-grade precancerous lesions that put women like me on that table. And there is emerging evidence of protection against oropharyngeal, vulvar, vaginal, and anal precancers and cancers, too.
Vaccinated girls and women have a 66% lower risk of invasive cervical cancer and an 80% lower risk when vaccination starts at or before age 16.
On the dose question specifically, the review found that a single dose may offer comparable protection to two- or three-dose regimens for some key outcomes in females. It also flagged the exact gaps that HHS skipped over. Limited evidence in males. Limited data on non-cervical cancers. Not enough long-term follow-up to know how durable single-dose protection truly is.
Getting the process right
The question of whether one dose is enough is legitimate. How HHS answered it was not. What should have come first is exactly what VIP has now done: a systematic mapping of what is known, what is plausible, and what evidence is still needed, with policy decisions left to the bodies that make them.
These updated findings should reassure people, not unsettle them. Public health authorities don't set out to maximize the number of shots a child receives; their goal is to recommend a schedule that maximizes protection against preventable diseases. The bottom line for the public health process is getting the recommendation right.
The HPV vaccine is itself proof that this process works. The original recommendation was three doses. In 2016, after evidence accumulated showing that two doses produced an immune response in 9- to 14-year-olds equivalent to or better than three doses in older adolescents, ACIP went through a formal evidence review and updated the recommendation accordingly. Same vaccine. Fewer shots. No drama. That is the model.
If the evidence on a single dose eventually supports another reduction, the recommendation will change accordingly. That will not mean the two-dose recommendation was wrong. It means the evidence base grew, and the recommendations were nimble and responsive to the evidence. That is how this is supposed to work.
This is not a vaccine where we are squinting at the data. We know the vaccine works. The ongoing debate is whether one dose is enough.
The need for uncomfortable conversations
And yet, the conversation around this vaccine still gets uncomfortable in ways the conversations around other vaccines do not. Parents who do not blink at the measles, mumps, and rubella or meningococcal shot get tense when HPV comes up. Pediatricians describe a kind of conversational tax they pay every time they bring it up at the 11-year-old well visit, because the parent in the chair is hearing "sex" and not "cancer."
I understand the discomfort. It is not easy to think about your child as a future sexual being. I have two children. I get it.
But is that conversation really harder than the one a parent has when their adult child calls and says, "stage 2 cervical cancer"? Or "anal cancer"? Or "throat cancer"? Australia responded to that question almost two decades ago when it decided the harder conversation was the second one and built a national program to ensure fewer families ever have to have it.
I understand the discomfort. It is not easy to think about your child as a future sexual being. I have two children. I get it.
The HPV vaccine prevents cancer. That is what 274 studies, taken together, are telling us. We have spent two decades accumulating evidence that the worst thing the vaccine does, for the overwhelming majority of people who get it, is make their arm sore for a day.
My son's appointment is soon. My daughter's will follow next year. Neither of them will remember it. That is the point.
Dr. Steier is a public health scientist and scientific communicator. She is the founder of Unbiased Science, an organization that uses data visualizations, real-world analogies, and human voice to communicate complex scientific concepts for public understanding via multiple media modalities.
The opinions voiced in CIDRAP Op-Ed pieces are the authors' own and do not necessarily represent the official position of CIDRAP.
