Double COVID-19 Vaccine Doses May Be Needed for Guaranteed Protection from Novel Coronavirus

A two-shot vaccine will be tougher to distribute widely and put developing nations at a particular disadvantage. There could be even more challenges if the vaccine’s efficacy reduces over time and annual inoculation is required, as suggested by some experts.

The latest results from clinical studies of COVID-19 vaccine candidates being developed by the University of Oxford (Oxford, UK) in collaboration with AstraZeneca (Cambridgeshire, England) and by Moderna, Inc. (Cambridge, MA, USA) appear to suggest the need for a double-shot vaccine regimen. Both the COVID-19 vaccine candidates are undergoing final-stage testing with two doses, as per the Bloomberg report. However, Oxford researchers believe that some recipients may acquire protection from a single dose and the results could indicate that a single shot could provide protection for the majority of people. AstraZeneca is exploring other regimens, although the company appears to be following a two-dose strategy and the first readout of its final-stage tests is most likely to be from two doses. On the other hand, Merck (Kenilworth, NJ, USA) has been focusing purely on one-dose shots as they can be deployed more easily and seamlessly across the world in a global vaccination campaign.

Similarly, CanSino Biologics Inc.’s (Tianjin, China) fast-moving COVID-19 vaccine candidate appears to prioritize a two-dose regimen as it seems to have failed to generate a strong response in people with pre-existing immunity to the novel coronavirus used as the vector, with researchers considering the use of a booster shot three to six months after vaccination. Following the news that 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, said, “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.”

“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,” added Rosenbaum.

Related Links:
University of Oxford
AstraZeneca
Moderna, Inc.
Merck
CanSino Biologics Inc.