The updated adult immunization guidelines came out this week so now is a good time to talk about vaccines. Actually, just last week, two colleagues asked me whether or not they should recommend their young patients get the newest 9-type HPV vaccine, even though they were vaccinated with one of the older versions (2-type or 4-type HPV vaccine) in the past. Patients, or parents of patients, have been asking about this because the newest HPV vaccine (Gardacil 9) protects against more types of the virus than the older vaccines (Gardacil protects against 4 types, and Cervarix protects against 2 types). The quick answer is no. But, before I explain why, I will give you some background about HPV, particularly it’s effects on the body, the vaccines available to protect against HPV, and the recommendations regarding vaccination.
Human papillomaviruses (HPVs) are widespread throughout the population. About 100 different types of HPV have been identified and 40 of them infect the genital area.
How does HPV affect the body?
HPV infection of the genital region is transmitted by genital contact, usually through sexual intercourse. Most infections are actually asymptomatic and have no long term effects. Infections on average last about 8 months, but can last up to 2 years. Infection with some types of HPV causes warts in the genital and anal areas. Sometimes the warts persist and need to be removed medically or surgically, but in many cases, the warts go away on their own. Other types of HPV can persist in the tissues causing abnormal cells which, after decades, can progress to cancer.
99% of cancers of the cervix are associated with high risk types of HPV. However, interestingly, most women with high risk types of HPV infection will never develop cervical cancer. This tells us that along with HPV, there are other factors which affect the development of cancer. Some of these factors include cigarette smoking, increased age, the presence of other sexually transmitted infections, use of oral contraceptions for a long time, and the presence of a weakened immune system.
Worldwide, 70% of cervical cancers are associated with 2 particular types of HPV (16 and 18). Ninety percent of anogenital warts are associated with 2 other types of HPV (6 and 11). With this knowledge, scientists were able to develop vaccines to protect against these high risk types of HPV.
Who should get the HPV vaccine?
HPV vaccination is recommended for females aged 9 to 26 years old, and for males aged 9 to 21 years old. Males aged 22 to 26 years who have higher than normal risk for HPV infection (such as those with weakened immune systems) should also be vaccinated against HPV. Ideally, HPV vaccine should be administered before potential exposure to HPV through sexual contact.
How is the HPV vaccine given?
Immunization with any of the available HPV vaccines, consists of 3 shots over a 6 months period. If for some reason the vaccination schedule is not completed within 6 months, there is no need to start over. The next dose just needs to be given as soon as possible.
Now back to the question posed at the beginning – if someone got one of the two earlier versions of the HPV vaccine, should they now get the newest vaccine which protects against an additional 5 types of HPV, for a total of 9 types? There is currently no recommendation to repeat vaccination with the newest HPV vaccine, in persons who previously completed immunization with one of the older versions. This is because, the majority of all HPV associated cancers are caused by 2 specific types of HPV (16 and 18). These 2 types are present in all three HPV vaccines. The additional 5 types of HPV in the new Gardacil 9 vaccine, cause only 15% of cervical cancers and pre-cancers. These 5 types cause an even smaller percentage of cancers in males. If a person were to be revaccinated with the newest HPV vaccine, studies have shown that there would be no adverse effect, other than increased pain and swelling at the vaccine site.
If someone started the vaccine series with one of the 2 older vaccines, the latest vaccine can be used to complete the series. However, there might not be full immunity to the additional 5 types of HPV. I suspect that eventually, the older HPV vaccines will be phased out.
Don’t forget your Pap smear!
Not to be forgotten, is the need for cervical cancer screening with Pap smears, even after HPV vaccination. This is because 30% of cervical cancers are due to HPV types other than those covered by the vaccines. Furthermore, persons sexually active before getting the vaccine could have already been infected by one of the HPV types in the vaccine. The vaccine has no effect on existing HPV infection of cervical abnormalities. Women should start having Pap smears at 21 years of age and at least every 3 years thereafter.
To conclude, the latest HPV vaccine is effective in preventing infection with 9 types of HPV. These types are responsible for about 85% of cervical cancers and 90% of anogenital warts. Persons vaccinated with one of the older HPV vaccines protecting against few types of HPV, do not need to get revaccinated with the newest HPV vaccine covering 9 types, since the most dangerous HPV types are prevented by all 3 available vaccines. Routine Pap smears are still required for all women, even after HPV vaccination.