Some of the results of the 1st interim assessment of the protective efficacy and safety of the Oxford vaccine ( AZD1222 ) against COVID-19 have been released today . So far, the information is far from complete and the picture is ambiguous. Three estimates of protective effectiveness have been published : 62%, 70% and 90%. The fact is that the structure of Phase 3 clinical trials of this vaccine is more complex than in the case of similar trials of other vaccines. This trial has been launched in several countries (United Kingdom, Brazil, USA, Russia, South Africa, Kenya), but the test protocols in different countries are not identical, and even within the same country, different immunization options are being tested. The released 1st Interim Analysis concerns only Phase 3 clinical trials in the United Kingdom (Project COV002) and Brazil (Project COV002).
In the COV002 trial, two immunization regimens were used, which differed in the dose of the vaccine in the first injection – half or full . The dose of the vaccine in the second injection was full for all and the interval between the 1st and 2nd injections was the same – 1 month. A licensed meningitis vaccine was used as a placebo in this trial.
The COV003 trial used one immunization regimen – the full dose of vaccine in both injections . The interval between injections was also 1 month. But placebo control was different: 1st injection – meningococcal vaccine, and 2nd injection – saline .
In total, at the time of the 1st interim analysis within the framework of the COV002 and COV003 trials, 131 cases of confirmed COVID-19 were registered among the subjects . Three calculations of protective efficacy were made , based on the distribution of these cases between the vaccine and placebo groups: the total and the two subgroups differing in the immunization schedule. The general calculation gave a modest, but formally acceptable value of protective efficacy – 70% (in this group at the time of assessment there were 11,636 subjects). But in the subgroups, the result was unexpected – the protective efficacy when using the half-dose immunization scheme in the first injection was significantly higher – 90% (in this subgroup at the time of the assessment there were 2741 subjects). A n rotektivnaya effectiveness two full doses was the lowest – 62% (in this subgroup, at the time of evaluation of the test was 8895).
This is definitely a surprise. On the one hand, it is a good surprise – half-dose immunization saves vaccine and reduces the cost of vaccination. On the other hand, this immunization regimen seems to be used only in the UK part of the trial. At least in the US portion of the trial, two full doses are used and this is likely to be the case in other countries where the trial is conducted. A difficult question arises – is it necessary to urgently change the test protocols in all these countries and switch to half the dose at the first injection? After all, the recruitment of volunteers has not yet been completed. Another question: who should make the decision – the ethics committee for this trial, located in the United Kingdom, or some national structure in the countries where the trial is taking place?
As for the safety of the AZD1222 vaccine, its assessment in the framework of Phase 3, in a period of 14 or more days after the second injection, did not reveal any serious problems . This analysis was carried out by an independent committee to monitor the safety of the trial.
The AZD1222 vaccine is less demanding on the transportation conditions (+2 – +8 degrees Celsius) and can be stored for up to six months in a regular refrigerator. The estimated price of this vaccine is $ 2.5 / dose, which is significantly lower than the estimated price of the Pfizer -BNT ($ 25 / dose) and Moderna ($ 15-25 / dose) vaccines .
In the near future, AstraZenaka is going to publish in a scientific journal the full data of the 1st preliminary evaluation of the effectiveness of their vaccine and apply for a temporary authorization for the use of the vaccine in emergency situations.
Supplement 25-11-2020. New information about the “half first dose of vaccine” subgroup – the age of the subjects in this subgroup was 55 years and younger, which introduces an additional unknown in the interpretation of the increased value of protective efficacy (90% in this subgroup). However, it should be taken into account that comparison of the immunogenicity of the AZD1222 vaccine in different age groups (18-55, 56-69, over 70) did not reveal a significant difference.