Despite its advantages over other vaccine technologies for Covid-19, adenovirus vector vaccines are likely to be tripped up by pre-existing antibodies to the vectors used and the need for a second injection to boost protection.

CanSino Biologics’ Ad5-nCoV and Johnson & Johnson’s AdVac platform-based vaccine use a human adenovirus vector, but a significant chunk of people may already have neutralising antibodies against the vector, decreasing efficacy prospects. Phase I Ad5-nCoV data is also underwhelming, adding credence to the issue of pre-existing antibodies.

AstraZeneca’s AZD1222 and Rome-based ReiThera’s Covid-19 vaccines are also adenovirus vectored but use nonhuman vectors. However, AZD1222’s recent animal data also leave questions about its utility to prevent virus spread. A possible way to improve efficacy is to add a booster shot down the line, perhaps using a different adenovirus vector or even a different vaccine technology. Perhaps AZD1222 only carrying SARS-CoV-2’s spike protein may not be enough.

There are at least 38 companies or universities with a recombinant adenovirus-derived vaccine asset for Covid-19 from preclinical to Phase II/III stages, according to GlobalData. AstraZeneca partnered with Oxford University on 30 April to further develop AZD1222, and on 3 June, the US Federal Government’s vaccine initiative, Operation Warp Speed, named it as one of five finalists along with Johnson & Johnson’s (J&J) candidate. Phase I/II AZD1222 trial (NCT04324606) data are expected shortly, while J&J’s Phase I/IIa will start in July. ReiThera will also begin a clinical investigation in the summer. CanSino is the only company that has released clinical trial data, with Ad5-nCoV already in a Phase II trial (NCT04341389) that has a primary completion date of January 2021.

AZD1222 is concurrently in Phase II/III trial (NCT04400838), with data timelines dependent on community viral transmission rates, the Oxford University website states. A registrational field trial expected to start in the summer is likely to require around 25,000–30,000 volunteers if the annualised incidence rate is 1.5%, this news service reported on 14 May. While a challenge trial design could be considered to quickly gather protection data, such a trial design also has its own operational and ethical issues.

Image Credit: Envato/ Amanda Scott

Read the whole article

News This Week

A DNA-based nanogel for targeted chemotherapy

Current chemotherapy regimens slow cancer progression and save lives, but these powerful drugs affect both healthy and cancerous cells. Now, researchers reporting in ACS' Nano Letters have designed DNA-based nanogels that only break down and [...]