It's 'a concern': Bavarian Nordic flags worrying COVID-19 vaccine result ahead of phase 3 data drop

Bavarian Nordic has identified a “concern” with its investigational COVID-19 vaccine. With phase 3 data imminent, the Danish drugmaker has reported weakened immune responses against the omicron variant XBB.1.1 in a midstage study.

Copenhagen-based Bavarian Nordic moved its viruslike particle COVID-19 candidate into a phase 3 trial in September in the belief it can provide broader, longer-lasting protection than existing products and thereby eliminate the need to keep adapting vaccines in response to new SARS-CoV-2 variants. The trial is comparing the candidate, ABNCoV2, to Pfizer and BioNTech’s Comirnaty when given as a booster.

Bavarian Nordic expects to report initial results around mid-2023. Ahead of the data drop, the vaccine developer has shared 12-month results from a phase 2 study, including an analysis of neutralizing antibody levels against the XBB.1.1 form of omicron.

The most recent data available show that an XBB variant called XBB.1.5 accounted for an estimated 92.9% of cases of COVID-19 in Europe over the second half of May. 

Recognizing the importance of efficacy against the XBB variants, Bavarian Nordic analyzed samples taken from subjects two weeks after they received the ABNCoV2 booster. The analysis found neutralizing antibodies against XBB.1.1 were induced in 43% of the 40 subjects “at levels associated with a reduced level of efficacy (78%) compared to the original Wuhan strain,” the company said. 

“While it is believed that the currently circulating XBB variants are less virulent, the weakened immune responses against this more distant variant is a concern and needs to be carefully evaluated in the ongoing phase 3 trial,” CEO Paul Chaplin said in a statement.

The 12-month results are more encouraging, although their significance for ABNCoV2 are questionable given the variants that are currently circulating. One year after receiving a ABNCoV2 booster, neutralizing antibodies against the Wuhan strain and the beta, delta and omicron BA.4/5 variants “remained at levels known to be associated with a high level of protection (>90%).”

If the neutralizing antibody levels translate into protection from infection or severe COVID-19, Bavarian Nordic could deliver on its goal of creating a durable vaccine. But the XBB.1.1 results raise doubts about whether the vaccine can end the need for variant-specific adaptations.