Trivalent hepatitis B vaccine appears more effective than existing options

18 Oct 2019 Liz Highleyman
Originally published on

Sci-B-Vac, an investigational vaccine that contains three different hepatitis B virus (HBV) proteins, may offer more protection, especially for older adults, than widely used existing vaccine options, according to late-breaking study results presented at the recent IDWeek 2019 conference in Washington, DC.

Hepatitis B vaccination has led to a dramatic drop in new infections worldwide. Immunisation is recommended in many countries for all infants, as well as for at-risk adults not vaccinated as children, including people living with HIV, gay and bisexual men, people who inject drugs, people with chronic liver or kidney disease and those at risk for HBV exposure through work or travel.

However, some adults who receive the standard three-dose HBV vaccine series do not achieve full protection, meaning they do not produce adequate levels of antibodies against the virus. This is more likely among older individuals and people with weakened immune systems. Further, protection has been shown to wane over time, leaving some people vulnerable years after they were immunised.

HBV vaccines currently approved for adults in the United Kingdom, including Engerix-B and HBVaxPro, are monovalent (single-target) vaccines containing a recombinant version of the hepatitis B surface antigen (HBsAg) known as small S. This antigen is also a component of the Twinrix dual hepatitis A and B vaccine as well as the Infanrix Hexa 6-in-1 vaccine for infants.

Sci-B-Vac, from VBI Vaccines, is a trivalent vaccine containing three HBV antigens: small S plus two larger viral surface proteins known as pre-S1 and pre-S2. Studies to date have shown that the combination induces more rapid and more complete protection, especially for people at risk for poor response to monovalent vaccines, and it may do so at a lower dose.

Prof Joanne Langley of Dalhousie University in Halifax, Canada, and colleagues conducted a multicentre randomised trial comparing a 10mcg dose of Sci-B-Vac versus a 20mcg dose of Engerix-B administered in three doses at the start of the study, on day 28 (about a month later) and on day 168 (about six months later).

The phase III PROTECT study included 1607 adults, including 42% in Europe, 42% in the US and 16% in Canada. About 60% were women, 19% were age 18 to 44, 45% were age 45 to 64 and 37% were over 65 years.

The study showed that Sci-B-Vac was non-inferior to Engerix-B, or matched its efficacy, among people age 18 and older, with 91.4% versus 76.5%, respectively, achieving immune protection when evaluated four weeks after the final vaccine dose (day 196). The seroprotection rate remained higher in the Sci-B-Vac group at day 336 (89.0% versus 68.8%, respectively).

Among participants age 45 and older, Sci-B-Vac reached the study's threshold for superiority at day 196 compared with Engerix-B, with seroprotection rates of 89.4% versus 73.1%, respectively.

Along with older individuals, response rates were also significantly higher with Sci-B-Vac among people with obesity (89.2% versus 68.1%), people with diabetes (83.3% versus 58.3%) and smokers.

Both vaccines were generally well tolerated with no notable safety problems, Langley reported. Adverse events were consistent with the known safety profiles of the vaccines from prior studies.

However, as VBI Vaccines announced earlier this year, the PROTECT trial did not meet a secondary endpoint of showing that two doses of Sci-B-Vac worked as well as three doses of Engerix-B.

Based on the results of this and the phase III CONSTANT trial, the company indicated that it plans to submit a request for approval of Sci-B-Vac to the European Medicines Agency and the US Food and Drug Administration by mid-2020. The new trivalent vaccine is already approved in Israel and ten other countries.

"Hepatitis B is one of the most serious global infectious disease burdens, and successful vaccination of both adults and infants is critical to controlling and, hopefully someday, eradicating the disease," study investigator Dr Timo Vesikari of the University of Tampere Medical School in Finland said in a VBI Vaccines press release. "If approved, this vaccine could play an important role in the prevention of hepatitis B, addressing a significant unmet medical need in the adult population."