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I marked a grim anniversary in an unexpected manner last week. On 18 January last year, I wrote my first story about a mysterious disease that had struck Wuhan, in China, and which was now spreading around the world. More than two million individuals have since died of Covid-19, almost 100,000 of them in the UK.
Remarkably, 12 months to the day that the Observer published my story, I was given my first dose of Covid-19 vaccine, allowing me to follow nearly six million other newly immunised UK residents who are set to gain protection against a disease that has brought the planet to a standstill. It was a rare, comforting experience after a year of unremitting sadness and gloom.
Not that the vaccine frees me up to have wild times. I am 70 after all. More to the point I have another two weeks until my first jab fully arms my immune system, before waiting for a second dose to seal the deal. And, even then, my continued risk of transmitting the virus – although unaffected by symptoms – means, quite rightly, that I am still subject to rules governing lockdown, mask-wearing and social distancing.
On the other hand, the vaccine has made me feel more secure. And by protecting people over the age of 70 – who account for vast numbers of Covid deaths in the UK – this should free up hospital beds and get our health service back on its feet. Normality might then return, albeit slowly.
Covid vaccines are a triumph of modern medical science, and the one beacon of hope we have in these dark days. But how, exactly, do they work?
My vaccine, made by Pfizer-BioNTech, contains genetic material that is known as messenger RNA or simply mRNA. These pieces are synthetic copies of mRNA found in Covid-19 viruses and are put in a protective chemical coat called a lipid. Injected into the muscle of my left arm, these pieces of mRNA were then swept up by tiny entities in my body called antigen-presenting cells.
The virus’s mRNA will then have been incorporated into these presenting cells’ own genetic material causing them to make pieces of viral protein. The cells, bearing viral protein, would then have been carried to my lymph glands in my armpits where my immune system should now be swinging into action. “The cells carrying viral protein tell your immune system there is something foreign invading your body and it is time it did something about it,” Professor Adam Finn, of Bristol University, told me. “This is done by switching on entities called killer T-cells. Only a small number among millions are chosen, however: the ones that are perfectly suited to tackle cells carrying the offending pieces of foreign viral protein that is presented to them. These few cells have been circulating in your body just waiting to be called into action. They are instructed to start dividing and to grow until millions of copies are made in a few days.”
This cellular armada of tiny killer T-cells will then sweep through my body to hunt out cells carrying offending virus particles, destroying them by issuing chemical instructions telling them to self-destruct. At the same time, another set of immune cells, known as B-cells, will start manufacturing antibodies specifically designed to latch on to pieces of viral protein and so block their action.
“This whole process takes two or three weeks to get under way,” added Finn. “If it were a real viral attack you might not have enough time to mount a defence and you could be swamped by invading viruses.”
However, by mimicking the Covid-19 virus, the vaccine is now preparing my immune system for an impending attack should I become infected one day.
Other vaccines, such as the Oxford-AstraZeneca version, operate in slightly different ways but are also designed to achieve the same goal – to stop Covid from gaining a beachhead in a person’s tissue before an all-out invasion. Dozens of other vaccines designed to trigger our antibody and killer T-cells are now in development. As government chief scientist Patrick Vallance put it last week: “We now have more vaccines than we could ever have dreamt of a year ago.”
But one question still concerns me about my Pfizer vaccine: just how well will I be protected against Covid-19? I ask because some reports say my first jab should give me at least 90% protection against serious illness; others say only 52%. Which is right? Vaccine efficacy is a critically important issue. It will determine how quickly and efficiently we get out of national lockdown and return to normality. The efficacy of a vaccine is calculated by comparing two groups of people: those who get the vaccine and those who get a placebo.
Infection rates for the two groups are measured daily. At first, there are no differences in case numbers because the vaccine needs time to take effect. This picture changes quickly, however. Slowly, infection rates decline in the first group as the vaccine takes effect, until, after three weeks, there are 90% fewer cases in the vaccinated group compared with the placebo group – hence the UK Joint Committee on Vaccination and Immunity’s statement that “vaccine efficacy from the first dose of the Pfizer-BioNTech vaccine is around 90%.”
By contrast, Pfizer takes the distinctly cautious approach of calculating efficacy from the day the first dose is given – when the vaccine has had no chance to provide protection and efficacy is zero. This process produces an average figure for vaccine efficacy of 52%.
The disadvantage of this approach is stressed by many scientists including UK vaccine expert Peter English. “If you include people who have not had time to respond to the vaccine then its efficacy obviously appears to be much lower. However, it is more appropriate to exclude them, as you wouldn’t have expected the vaccine to have worked yet.”
Why Pfizer takes this approach is a matter of some conjecture but the message is clear as far as I am concerned. I will have 90% protection against Covid-19 in another couple of weeks. So am I concerned that I will have to wait a couple of months more to get my second dose? No, I’m not. My existing protection should last well beyond that time.
Not everything will be plain sailing, of course. New variants of the Covid-19 virus are appearing. At present, there is no evidence that existing vaccines will fail to neutralise the variants observed so far in the UK. But scientists are concerned that a new strain could evolve in future and evade current immunisations.
“It is a genuine concern,” said Finn. “A new variant could start to avoid antibodies triggered by your vaccine. However, you will still have T-cells to mount a defence, and that means that the immunity provided by the vaccine you got last week is very unlikely to become completely useless should such a variant appear.”
It is not a blanket reassurance. But given what we have all endured over the past year, I am going to accept, with considerable gratitude, what Covid vaccines will do for my health, and for the wellbeing of others.
Source: The Guardian
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