CanSino first with Phase II COVID-19 vaccine results, but one shot might not be enough, says GlobalData

Following the news that Chinese biotech CanSino published Phase II results of its COVID-19 vaccine candidate Ad5-nCoV;

Philipp Rosenbaum, PhD, Senior Infectious Diseases Analyst at GlobalData, a leading data and analytics company, offers his view:

“With one dose, CanSino’s human adenovirus vector-based vaccine elicited receptor-binding and neutralizing antibodies in 508 patients peaking after 28 days. However, in the 52% of study participants that had a high pre-existing immunity to the viral vector, both types of antibodies were only at half the level than in the group with low-pre-existing immunity. A second dose of the vaccine might solve this issue, but on the other hand reduce the number of people who can be vaccinated.

“Furthermore, trial participants older than 55 years of age showed lower antibody responses than younger participants, possibly correlated with higher pre-existing Ad5 immunity, which is a serious issue since older people are particularly vulnerable to SARS-CoV-2 infections. Additionally, the percentage of trial participants who produced neutralizing antibodies was low with 48% in the low-dose and 52% in the high dose group.

“Higher vaccine doses usually lead to more adverse events, so one solution might be for the elderly to generally receive two doses of the vaccine and younger people only one dose, to measure pre-existing Ad5-vector antibodies and then decide how many doses will be needed, or to add an adjuvant to boost the immune response.

“Nevertheless, the results are promising and warrant studies with more participants, longer observation of antibody levels and multiple vaccine doses – given the urgent need for a COVID-19 vaccine. Since CanSino is the first company to publish Phase II results, it has to been seen how the level of antibodies and T-cells will compare to results of COVID-19 vaccine candidates from other companies. However, it is still unclear which antibody levels will provide protection against SARS-CoV-2 and for how long this protection will last.”

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