In a press release today, AstraZeneca reported its AZD1222 vaccine against SARS-CoV-2 is ready to report efficacy levels.
As the two tweets above demonstrate, the two very different figures of 70% and 90% came out by separate news agencies. The discrepancy, it turns out is related to variations in how the vaccine is administered.
The variations are summed up by AstraZeneca in the original press release:
One dosing regimen (n=2,741) showed vaccine efficacy of 90% when AZD1222 was given as a half dose, followed by a full dose at least one month apart, and another dosing regimen (n=8,895) showed 62% efficacy when given as two full doses at least one month apart. The combined analysis from both dosing regimens (n=11,636) resulted in an average efficacy of 70%.
Shortly after initial announcements, some news agencies moved to clarify the confusion in response to negative public perception of media integrity.
AstraZeneca closely follows the announcement by Pfizer who with the firm BioNTech released news of a 90%+ effective vaccine.
Following Pfizer's announcement, several members of the Trump family and administration credited the US president's Operation Warp Speed's "tireless work" to support the creation of the vaccine. However, Pfizer was only a participant in the program in terms of a conditional purchase agreement, rather than funding.