AstraZeneca and the University of Oxford are likely to conduct a further global study of their Covid-19 vaccine candidate AZD1222, which would evaluate an initial low-dose of the vaccine. Both companies have been criticized for their data earlier released in November, in which the lower dose of AZD1222, given to study participants in error, performed better than the full amount.

When AstraZeneca and the University of Oxford presented the results, they highlighted a combined interim analysis from two late-stage studies conducted in the UK and Brazil suggesting that AZD1222 had an average efficacy of 70%. However, the data showed that efficacy of the vaccine when administered as a half dose followed by a full dose in 2741 people was 90%, dropping to 62% in 8895 participants given two full doses. The parties later disclosed that the regimen in which subjects initially received a half dose of AZD1222 was in fact due to a dosing error. These omissions have sparked a storm of criticism over transparency,

According to AstraZeneca CEO, Pascal Soriot, the additional study should not delay regulatory approval of AZD1222 in the UK and Europe. Authorisation in the US should take longer as the FDA is unlikely to accept the current data.

Why does AstraZeneca-Oxford's vaccine candidate really have good chances to get to the market and to save lives, despite what may appear as disappointing results? Phase III data for the vaccine, which uses a novel chimpanzee adenovirus vector, is expected to read out before the end of the year.

Above all, there are other success factors to take into account: safety is one, with no serious side-effects reported. Storage is another one, as the Oxford vaccine can be stored in a domestic fridge, while other treatments require a storage temperature as low as -70 C. Based on viralvector, it is also cheaper, with the jab priced at about $3 to $4 per dose, much less than the other vaccines (respectively 20 and 33 dollars for Pfizer and Moderna).

Moreover, in Phase 2 trial results, the vaccine had fewer adverse effects in older people than in younger adults, and produced a similar immune response in both groups. But questions still remain about effectiveness and length of protection. The two companies said they will bring answers before the end of the year. AstraZeneca and manufacturing partners hope to produce up to 3 billion doses next year.

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