In 2006, a vaccine called Gardasil made its debut. Its ability to protect against two of the most widespread strains of human papillomavirus (HPV) means that it doesn’t just protect against an infectious disease — it protects against cancer, too. A persistent HPV infection can trigger cell changes that could lead to cancers of the mouth, throat, cervix, vulva, anus, or penis. Gardasil also protects against two additional strains of HPV that cause most genital warts.

The most common Gardasil side effects are fainting, dizziness, nausea, headache, fever, and hives, as well as possible pain, redness, or swelling at the injection site.

Cervical cancer is not as common in the developed world as it once was, thanks to an effective screening test. The Pap test catches “precancerous” cell changes, allowing the precancer to be treated before it develops into full-fledged cancer. So, while HPV vaccines have the potential to save hundreds of thousands of lives if they can be distributed in countries without widespread access to Pap testing, they have utility in the United States, too. Gardasil has spurred declines in high-risk HPV infections and genital wart incidence among American girls — which means less “precancer” and all the invasive, possibly expensive or painful, treatments that they entail, and a lot fewer genital warts. What’s not to like about that?

Despite this, a lot of people are curious about Gardasil’s side effects. If you enter a few key search terms into Google, you can easily find all kinds of websites warning you of Gardasil’s alleged dangers. So, you might be wondering: Is Gardasil safe?

What are Gardasil’s side effects?

Despite Gardasil’s relatively recent debut, many studies have already been conducted to evaluate its safety — and research continues so that we can consistently reassess its risks and benefits. So far, the consensus is that Gardasil is safe, with very few side effects. According to the Centers for Disease Control and Prevention, the most common Gardasil side effects are fainting, dizziness, nausea, headache, fever, and hives, as well as possible pain, redness, or swelling at the injection site. These reactions are not considered to be serious, some people don’t experience any of them, and they are only temporary.

Many large studies have investigated whether Gardasil increases risk for more serious side effects. While all of these studies were large, one examined the medical records of nearly 1 million girls in order to compare those who received Gardasil with their unvaccinated counterparts. Such huge numbers are more likely to reveal rare side effects, if they exist. However, these studies all found that vaccination doesn’t increase risk of developing serious conditions like Guillan–Barré syndrome, stroke, venous thromboembolism (VTE), appendicitis, seizures, allergic reactions, anaphylaxis, or other autoimmune or neurological diseases.

One study of 189,629 female Gardasil recipients found only two risks associated with Gardasil: skin infections within two weeks after receiving the injection, and fainting the same day of being vaccinated. These risks were very small. For example, only 23 people fainted after receiving Gardasil — that’s 0.0001 percent of all vaccine recipients! (The increased risk of skin infections might raise the old eyebrows — with proper injection practices, such infections should be minimized.)

A 2011 meta-analysis pooled the results of seven clinical trials of HPV vaccines (including Gardasil, as well as a less-utilized HPV vaccine called Cervarix), which were conducted on a total of 44,142 females, some of whom received the HPV vaccine and some of whom received a placebo shot. The risk of serious side effects was not found to be different between people receiving the vaccine and the people receiving a placebo. The most common side effect was pain at the injection site, as well as headache and fatigue — all of which were experienced by people receiving the vaccine as well as those receiving the placebo.

But maybe you’re not worried about a headache or a little dizziness. Maybe you’ve heard horror stories about way scarier side effects, like infertility or even death! What should you know about these claims?

Does Gardasil cause infertility?

There are a couple of case studies in medical journals describing ovarian failure in teenage girls after receiving the HPV vaccine. When put into context, in which millions of Gardasil doses have been administered, these occurrences seem much more likely to be coincidental. In the United States, 1 out of 1,000 females experiences ovarian failure before turning 30, and the overlap between this group and the Gardasil-receiving population makes it possible to cherry-pick cases and assert a cause-and-effect relationship.

The origins of this myth are surprising — one of the case reports originated from researchers whose anti-vaccination views are well outside of the mainstream. The other case report was authored by an anti-abortion activist affiliated with an organization that opposes many sexual and reproductive health services. It’s important to point out that, while there is no evidence that Gardasil interferes with fertility, it does protect against HPV infections — which themselves can lead to infertility.

Can Gardasil kill you?

Forty confirmed deaths have occurred among the tens of millions of U.S. Gardasil recipients. These deaths didn’t necessarily occur immediately after vaccination, either, but could have happened weeks or months afterward. Most important, not one of these deaths was found to have been caused by vaccination — causes of death included bacterial infection, prescription drug abuse, influenza, heart problems, and suicide. Of course it’s always tragic when a young person dies, but investigators did not see any red flags that might indicate that deaths following vaccination were due to anything other than coincidence.

At last count, about 57 million doses of HPV vaccines have been given in the United States. All vaccines can have side effects, but severe side effects are rare, and the more common side effects aren’t as serious as the diseases these injections prevent. For example, most people would probably rather be dizzy for a few minutes than have to follow up an abnormal Pap test with a colposcopy, or ask a dermatologist to remove warts from their genitals.

Planned Parenthood health centers offer Gardasil. More information is available from Planned Parenthood, the National Cancer Institute, and the CDC.

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