Single Dose of HPV May Prevent Cervical Cancer

Just one shot of the HPV vaccine in adolescent girls may be required to prevent cervical cancer, revealed new study. However, it does not advise immediate change in the current recommendations. Cervical cancer, that is, cancer that affects the lowermost narrow part of the uterus, is a very common cancer in females. It is rated as the fourth most common cause of cancer death in the world. Women in poorer countries are more commonly affected. This cancer has been found to be associated with HPV or human papilloma virus infection. The virus spreads through sexual contact. There are several types of cancer-causing HPV viruses. HPV type 16 is responsible for about 50% of cervical cancers, while HPV-18 causes around 20% cases. The remaining cases are caused by other HPV viruses. Vaccination with HPV vaccine can thus prevent HPV-related cervical cancer.

The HPV vaccine is administered in 3 doses over a duration of 6 months to girls around the ages of 11-12 years so they can be protected before they are sexually active. There are two brands of HPV vaccine available – Gardasil and Cerivax. In Britain, a 2-dose regimen is also approved. These doses are given 6 months apart.

In a recently published study from Lancet Oncology, researchers combined and analysed data from the Costa Rica Vaccine Trial (CVT) and PATRICIA trials. Young women in the age group 15-25 years received the Cerivax vaccine. The women had to receive three doses of the vaccine, however several did not complete the vaccination schedule and therefore received only one or two doses. The number of women receiving a single dose was quite small as compared to those receiving 3 doses.

After a period of 4 years, the researchers found that the effectiveness of the vaccine was between 77 and 86%, irrespective of how many doses the women received. Though the antibody titre in those receiving one dose in the CVT trial were lower than those receiving two or three doses between months 6 and 48 of the study, it provided adequate short-term protection. In those who received 2 doses, the vaccine was more effective if the gap between the vaccines was 6 months rather than 1 month.

The effectiveness of the single dose could be due to the viral particles in the vaccine or the adjuvant, which is added to the vaccine. If it is due to the viral particles, other HPV vaccines may also have the same effect. If the effect of a single dose is due to the adjuvant, the effect will be exclusive to Cerivax.

The study is significant since it could bring more girls under the ambit of HPV vaccination. In many places, people may not be able to afford the cost of 3 doses. Thus, it would be good news to them if only one dose would suffice. However, further studies are necessary to confirm that the single dose would be effective over a longer period.