[nudephil (OP)]

Here's a question from listener Dave:

With the possibility of multiple COVID-19 vaccines becoming available via different technologies, will there be an advantage in having a vaccination from different sources to improve efficacy?

[chris]

Actually, the approach of mixing vaccines of different types is an established vaccination strategy. It's called "prime boost immunisation". The rationale is that you use one vaccine to stimulate an initial response which you then broaden and consolidate with the administration of a different vaccine that features overlapping but different antigens.

Therefore, there might be merit in mixing and matching between vaccines, but for simplicity of deployment the strategy used in the first instance will be to give people the clinically tested and approved regimen of their (probably) two doses, a month or so apart.

[evan_au]

I think it will be a challenge to get a vaccine that has been through a solid phase 3 trial, in sufficient quantities to vaccinate everyone once.
- Running a significant Phase 3 trial on a combination of vaccines is not in the interests of the individual vaccine makers.
- Having the option to be vaccinated twice is a luxury that some rich individuals might buy, but is unlikely to be funded by governments.
- If they track who receives which vaccines, after a while there may be enough people who have tried 2 vaccines to be able to certify the effectiveness of the combination

However, if the immune response gets weaker over a few months, or the virus mutates sufficiently that the original vaccines are no longer effective, then multiple vaccinations may become necessary, and validating the combination of vaccines will become a essential.

[chris]

Actually, most of the vaccines being tested at the moment rely on a two-dose regimen with 3 weeks between doses. Therefore mixing and matching is not such a perverse prospect, and of the two genetic vaccines with results declared so far, most of the immune heavy-lifting appears to be arising from the first dose. Nevertheless, it would be a logistical headache to mix up vaccines, so not worth it...

C

[alancalverd]

Not a great logistic problem.

There must be some means of certification and tracking. Suppose we have 3 acceptable products available for free public vaccination. On your first appearance you will fill in a card with whatever ID is appropriate, and you can choose to join queue A, B or C. Your card will be stamped A/B/C and scanned on injection, you take it away and you will be invited to choose any queue on your second appearance, with a note that this is a clinical trial to investigate the relative effectiveness of A, B, C and all combinations of two vaccines. Scan and stamp the card again.

Result: a 100% random sample of every possible combination, at no cost or effort.

The tactical logistics of cold chains and mass vaccination  have been solved by WHO, Oxfam, MSF and  pretty well every other medical charity. The UK presents fewer problems than most.

Suppose we open three queues at the gate of a military camp, just like a ferry terminal. You printed off your card at home and were given an arrival slot. Drive in, check paperwork, get the jab, stamp the card, then drive to a holding line on the parade ground/dock/runway where you wait for 10 minutes until release if there are no allergic symptoms. No problem of isolation as each family group stays in their own vehicle. That should take care of 90% of the population, in and out in 15 - 20 minutes.   

[set fair]

A potential advantage to using different vectors is that you avoid an immune response to the vector, in the second jab, lessening spike protein production. I understand the Russians are using two different adinoviruses.