Chinese researchers have taken a major step forward in developing a new-generation vaccine that has the potential to protect against almost all of the most potentially lethal forms of human papilloma virus (HPV).

HPV is primarily transmitted through sexual contact. More than 200 distinct HPV types have been identified, of which at least 18 are high-risk types associated with 99 percent of cervical cancers, the second most common cancer among women, after breast cancer.

Gardasil 9 is the current market-available HPV vaccine providing the broadest protection against infection from nine HPV types, seven of which can cause 90 percent of cervical cancers.

However, it remains unclear whether widespread immunization with vaccines like Gardasil 9 could lead to an increase in infection rates from the other cancer-related HPV types, responsible for the remaining 10 percent of cervical cancers.

To expand type coverage, the approach used in previous-generation vaccines was to increase the number of virus-like particles. One particle resembles one HPV type, and it can elicit immunity to one HPV type. The more particles a vaccine has, the broader protection it provides.

However, this approach is fraught with difficulties, as an increase in type coverage will dramatically enhance protein amounts and immunological agent levels per dose, which will cause side effects, such as pain, swelling and fever, and raise the manufacturing complexity and production costs.

Researchers at Xiamen University, in east China's Fujian Province, have developed a highly effective vaccine candidate that can protect against more HPV types with fewer particles.

They divided 20 major HPV types, including HPV6 and HPV11, which accounts for 90 percent of genital warts, into seven groups based on genetic relationships, and found that genetically close HPV types shared high structural similarities.

Xia Ningshao, lead researcher, compared the virus or the vaccine to a "ball". All HPV types are similar in appearance, but are significantly different in the surface of the "ball", such as veins, convex and concave areas. These structural features on the surface are called loops.

"Because of the loops, one type of vaccine can stimulate the production of antibodies only against the infection of one type of virus, and is unable to prevent the infection of other types," he said.

Using a loop swapping approach, researchers engineered a complex virus-like particle with the loops of three genetically close HPV types: HPV33, HPV58 and HPV52.