GUWonder

AstraZ's vaccine is being reported as being something like 60% effective and 90% effective depending on which of the two research arms is examined. Not as highly effective as Pfizer-B's vaccine or the Moderna vaccine, but still effective enough to be very helpful.

I do have to wonder if some people will choose to get two different types of vaccines for this and how that will play out.

fransknorge

AstraZenecca vaccine also is one jab and does not need anything special for storage as opposed to the two other needing -80 degrees Celsius. It has more potential for certain countries and can be distributed quicker.

GUWonder

The Pfizer-B and Moderna vaccines require a sequence of two vaccine shots per patient, and those mRNA vaccines do indeed have much more costly handling needs due to the hyper-specialized freezer needs. The AstraZ vaccine was developed with a different approach than the mRNA ones.

dorisrpas

This article suggests it requires two doses, or am I reading something wrong?

https://www.cnn.com/2020/11/23/europ...ntl/index.html

GUWonder

That article does indeed suggest AstraZ is also two shots: one approach involving half a dose shot followed by a full dose; alternative approach one full dose shot followed by another full dose shot some weeks later.

fransknorge

Correct. I misread.

corporate-wage-slave

All of Oxford-AZN Phase 3 was done with 2 injections, the second injection 21 to 30 days after the first. There were two main subgoups here, one group (the larger one) got two full doses. The other group got a half dose and then a full dose for the second injection. This group was arranged because the immunity response to different dosing levels is a well known phenomena. The half + full group got 90% efficacy. the full + full doses group had 62%, the overall figure thus being 70%. That 70% figure may not be useful since there isn't an implementation method that would get you to 70%, the choices are 62% or 90%. Since 90% will require less vaccine while it is still under manufacture, then this is a good outcome in that it nearly doubles the first round of potential recipients.

ryman554

Of course, the stupid question is:

Which one was 90% effective, and which one was 62%?

I could always assume, but you know what that makes out of me. But, if the half dose is really that much less effective, that does tell you something about reinfection probabilities as compared to severity of the illness, yes?

TTT

I've read a hypothesis on the 0.5+1 dosing vs the 1+1 dosing being more effective because of an immune response to the adenovirus vector. Essentially, the 1+1 dosing generates a too strong immune response to viral vector in the full first does so that the second booster is less effective.

Is that an issue with other viral vector vaccines?

corporate-wage-slave

Potentially yes, but there are only 2 other viral vector vaccines in Phase 3 at the moment, Johnson & Johnson and, um, Sputnik V. These two are non-replicating, whereas Oxford-AZN is a replication-deficient viral vector vaccine. Pfizer and Moderna are messenger RNA so have a different approach. There are more viral vector vaccines in Phase 1.

TTT

I'm more curious about experience from vaccines for other diseases. Does viral vector immunity impact those?

GUWonder

The half-dose+full dose came off as being significantly more effective (i.e. c. 90% effectiveness) than full dose+full dose (i.e. c 62% effectiveness).

corporate-wage-slave

Yes, the similar vaccine for pulmonary tuberculosis has shown in trials that different - and often lower - doses can improve efficacy. The idea is to mimic how natural immunity works, which is sometimes compared to waves of different strengths, ebbing and flowing.

TTT

Thanks - that's a good explanation.

cockpitvisit

According to the AstraZeneca press release, about 2,700 persons got half dose+full dose. Not sure what the infection rate of the control group was, but with the Pfizer trial, it was less than 0.5%. This would mean 13 infected persons out of 2,700. A 90% effective vaccine would mean one infection per 2,700 people, a 70% effective vaccine would mean 4 infections. Doesn't seem statistically significant to me... looks more like a fluke.