Have you ever heard of the “HPV virus” or Human Papillomavirus? This is a very common virus that spreads through sexual contact—whether vaginal, anal, or even oral. Once inside the body, HPV can enter cells and disrupt their normal function, causing abnormal cell growth that may spread to surrounding tissues. If left untreated, it can eventually lead to serious diseases such as cancer.

There are more than 100 types of HPV, but around 30–40 of them are associated with diseases in humans. These are divided into two main groups. The first group includes low-risk types, such as types 6 and 11, which typically cause genital warts, as well as warts in the mouth, anus, or urethra. Although not usually dangerous, chronic infections with these types may still increase the risk of developing cancer.

The second group includes high-risk types, such as types 16 and 18, which are responsible for about 70% of cervical cancer cases. According to Thailand’s National Cancer Institute (2010), cervical cancer is the second most common cancer among Thai women, after breast cancer, and claims an average of 14 lives per day.

The best way to prevent HPV-related diseases is to reduce risky behaviors such as having multiple sexual partners and to use condoms consistently. Another highly effective preventive measure is the HPV vaccine, which can protect against up to 90% of infections. Cervical cancer is currently the only type of cancer that can be prevented with a vaccine.

The HPV vaccine works by using a harmless viral protein to stimulate the body’s immune system to produce antibodies against HPV. This helps significantly reduce the risk of infection and cancer development. Since HPV vaccination was first introduced in 2006, HPV infection rates have dropped by 88% among teenage girls and by 81% among adult women.

Currently, there are three types of HPV vaccines available: 9-valent, 4-valent, and 2-valent. All of them protect against types 16 and 18, the main culprits behind cervical cancer. Long-term studies have shown that immunity remains strong for at least 10 years after vaccination and may last a lifetime without the need for booster doses.

In Thailand, HPV vaccines are approved for both women and men. The 2-valent vaccine is for women aged 10–25, the 4-valent vaccine for women aged 9–45 and men aged 9–26, and the 9-valent vaccine for broader coverage. The Pediatric Infectious Disease Society of Thailand and the Subcommittee on Gynecologic Oncology recommend vaccination between ages 9–26, with the ideal age being 11–12, when the immune response is strongest and before sexual debut.

Even those who are already sexually active can still benefit from vaccination, though it may be less effective than in individuals who have never been exposed to HPV. Vaccination is also recommended for people with weakened immune systems, such as those with HIV, or women with precancerous cervical lesions, abnormal Pap smear results, or positive HPV tests. For women aged 26–45 or those already sexually active, a doctor’s consultation is advised to weigh the risks and benefits.

Importantly, HPV vaccination is not just for women. Men can also contract HPV, often without symptoms, making them silent carriers who unknowingly transmit the virus to others. Vaccinating men helps protect not only themselves but also reduces the spread to their partners.

As for side effects, HPV vaccines are generally safe. The most common reactions include mild pain or swelling at the injection site, low-grade fever, dizziness, or fatigue—all of which resolve within a few days. Severe allergic reactions are extremely rare. The vaccine should not be given to individuals with a known allergy to vaccine components (such as yeast) or those who have experienced severe allergic reactions in the past. It is also not recommended during pregnancy, but women planning pregnancy may receive the vaccine beforehand with at least one month of contraception.

Even after vaccination, regular cervical cancer screening (Pap smears or HPV testing) remains essential, since the vaccine does not cover all HPV types. Routine screening ensures that any abnormalities are detected early, when treatment is most effective, preventing the progression to cancer.