Tag Archives: mRNA

more on vaccines

nice image showing the storage requirements of the two vaccines soon to be available in Australia – filched from the ABC

While I’m on vaccines, the Oxford vaccine is another. A friend sent me a link to an article in The Independent, a UK newspaper, headed ‘Oxford scientists preparing to design new versions of Covid vaccine in response to variants’. Variants are cropping up around the world at the moment, the UK variant (called B117) being followed by a South African and Brazilian variant. That’s unlikely to be the last of them. However the three leading lights re covid19 vaccines, Oxford/AstraZeneca, Pfizer/BioNTech and Moderna, all say they’ve got B117 covered, and presumably are confident about other variants. Of course the key is whether adjusted vaccines can be produced rapidly in sufficient quantities.

However, there are other issues. The possible proliferation of variants raises the question of whether we can successfully vaccinate our way out of this pandemic. The South African variant (501Y.V2) is particularly concerning, as some patients’ antibodies, after treatment, are not recognising it. It isn’t yet clear how significant this development is.

So while we await developments, I want to look at the Oxford/AstraZeneca vaccine (ChAdOx1) in a bit more detail. A few basic facts. It has been developed from a chimpanzee adenovirus, a type of DNA virus that causes relatively mild symptoms in chimps (we know of over 60 adenovirus types, many of which cause cold and flu-like symptoms in humans). It’s the vaccine of choice of the British government, unsurprisingly, and some 100 million doses have been ordered so far. It’s also cheaper (at $3 to $4US a dose) and easier to store than the two other major vaccines, which makes it the best option for poorer nations. AstraZeneca has promised to always sell the vaccine at cost to those nations.

The adenovirus has been altered to include genetic material from SARS-CoV2, so as to evoke an effective antibody and T-cell response to that virus – which has presumably been tested in clinical trials. The vaccine is described as up to 90% effective, depending on dosage, a lower percentage than the other two more expensive vaccines I’ve mentioned. Other vaccines, including Russia’s Sputnik-V and the Johnson & Johnson vaccine, have been developed from adenoviruses. Oxford researchers have found, unexpectedly, that giving a half-dose, followed weeks later by a full dose, improved efficacy by up to 90%, compared to 62% for two full doses. The reason for this result remains a mystery – further research required. It should be noted that vaccines with 60-70% efficacy are generally regarded as successful.

As I write, I’ve heard that Australia’s medical regulator, the Therapeutic Goods Administration (TGA) has approved the Pfizer vaccine for use here. Ten million doses will be rolled out in late February, after batch testing by the TGA. Why did they approve this version first? That will require further investigation, but I suspect that the greater flexibility of this new mRNA technology – all they need is the genetic sequence of a new SARS-CoV2 variant to create a vaccine to cover it – might have been a deciding factor.

However, it may well be that the Oxford/AstraZeneca vaccine, which should be approved soon, and which has been put on order, will be the most widely available, due to ease of storage and a cheaper price tag. Australia is able to manufacture this vaccine locally, so that supply shouldn’t be a problem.

Other issues – which authorities are not so willing to discuss given the need to protect high-risk individuals at the outset – are the vaccination of children, and how to deal with vaccine reluctance, or hesitancy, the new buzz-terms for anti-vaxxers. This leads to the issue of herd immunity, which I’ll discuss in my next post.