Another half a million or so people will today bare their shoulder and have a vaccine against COVID-19.

It’s a triumph of science and logistics. But will it end the pandemic?

Just a few weeks ago the answer would have been an unqualified “yes”. But the evolving virus has knocked the confidence of many scientists.

The clinical trial of the AstraZeneca/Oxford vaccine in South Africa underlines why they are concerned.

Up until the end of October the jab was proving to be 75% effective after a single dose.

But since then a new variant of the virus has led to a surge of cases.

Results from the trial show that the vaccine is now just 10% effective at preventing mild or moderate disease in the South Africa variant.

It’s a dramatic fall in the vaccine’s efficacy.

But it’s not mild or moderate infections that put people in hospital, so does it matter?

The researchers in South Africa don’t yet have direct evidence of how effective the vaccine is in preventing severe cases.

Instead they point to a clinical trial of the up-and-coming Johnson & Johnson vaccine which was also done in South Africa while the new version of the virus was spreading.

It uses very similar vaccine technology as the Oxford jab, so it’s a good comparison.

The results showed that it prevented 89% of severe disease, so nine out of 10 cases that are likely to lead to hospital admission.

If that was also true of the Oxford jab it would be an enormous relief.

The problem of variants isn’t unique to the Oxford vaccine. All the jabs target the same spike protein on the virus.

The Pfizer/BioNTech jab has yet to be tested against the South African virus in a clinical trial, but small-scale lab tests showed people produced far fewer antibodies that were able to kill the virus. The belief is that the vaccine would still be protective, but it’s impossible to say for certain.

Here in the UK there are just 147 known cases of the South African variant. Most are travellers from southern Africa, or their close contacts.

But the virus is now starting to spread in a number of locations around England, in people with no travel history.

And the mutation that reduces the effect of the vaccines, called E484K, has spontaneously evolved in the original version of the virus in Liverpool, and in the Kent or UK variant in Bristol.

There are only a small number of people identified with the newly mutated viruses so far, but there are likely to be many more cases going undetected.

That’s why so much effort is going into surge testing in areas where the viruses are known to be spreading.

I’m not making an argument for giving up on immunisation.

The vaccine is highly effective against the dominant strains spreading in the UK.

And the faster the number of cases come down the lower the opportunity for the virus to mutate further.

So the vaccine is well-worth having.

But all the pharmaceutical companies will have to update their jabs to stop the virus getting away.

It’s straightforward to do. But it will take time.

Even if minimal additional testing is needed for the vaccine to be approved by the regulatory authorities, it still takes two months from start to finish to make the Oxford jab.

And there is an element of crystal ball gazing required. Who is to say that the South African variant is still the one to watch next winter? Will it be overtaken by another variant?

So it may be prudent to think again about our vaccines. Is it enough to base protection on the genetic blueprint for one protein from one virus?

Should the manufacturers think about covering a range of mutated variants, in a similar way to the flu jab?

Or maybe they should build in the insurance of another target in the virus that doesn’t mutate as fast as the spike protein.

In the meantime, if you are due to have your jab, line up with confidence.

But expect to be baring your shoulder again come the autumn for a booster against the shape-shifting virus.

Over three nights Sky News will host a series of special programmes examining the UK’s response to the pandemic.

Watch COVID Crisis: Learning the Lessons at 8pm on 9, 10 and 11 February

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