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While the political and economic consequences of Covid-19 continue to hang over the world like an autumnal mist, scientists are making progress in understanding the effects of the virus and

how we can fight it. Unfortunately, not all their results are encouraging: it sometimes feels as though humanity takes two steps forwards, then one step back. Yet even when research appears

to close off one avenue, another opens. This week three major studies have shone new light on the pandemic. First, the bad news: according to a joint study by brain scientists at Imperial

College and King’s College, London, Cambridge and Chicago Universities, those who recover from Covid are likely to experience long-term cognitive impairment. “Long Covid” or “brain fog”, of

which there is anecdotal evidence months after recovery, is real. In the worst cases — those who require intensive care, often on ventilators — the mental decline can be the equivalent of

ageing ten years, or an 8.5 point fall in IQ. Even those who experienced no breathing difficulties and recovered at home averaged a deficit equivalent to ageing five years or an IQ drop of

four points. Two important caveats should be mentioned here. Covid-19 has not been with us for long enough for scientists to be able to predict whether the mental decline it causes in

sufferers is temporary or permanent. And time spent in intensive care or on a ventilator for any disease affects cognitive function. More than 84,000 people took part in the study, but only

60 were cared for on a ventilator and 147 were hospitalised; 176 were treated at home while 3,466 recovered at home from breathing difficulties without medical aid. A much larger number —

9,201 — were ill but had no respiratory problems. The initial study took place in May and further work is needed to assess the long term impact. But the implication of this research is that

allowing the population to catch Covid-19 could impose too great a cost in mental health. A second major study suggests that “herd immunity” to Covid-19 may not in practice be achievable

because antibodies and immunity decline rapidly after recovery. Scientists at Imperial College screened 365,000 people over three months from June to September. They found that when lockdown

was eased in late June and early July, 6 per cent of the population had antibodies. But by the time the second wave began in September, just 4.4 per cent were found to have antibodies. This

suggests that the human body reacts to Covid-19 as it does to other coronaviruses, including the common cold. We are regularly reinfected with these viruses, rather than building up

long-term immunity. Both these studies are a blow for the minority of scientists who propose that we should allow more than half of the population to be infected, while shielding the most

vulnerable, in order to create herd immunity. Nevertheless, Professor Sunetra Gupta of Oxford and other signatories of the “Great Barrington Declaration” deserve to be given a chance to take

both studies into account in adapting their proposals, which aim to avoid the damage caused by lockdowns to health and the economy. The third study to be announced this week has better news

for us all. Preliminary results from trials for the promising new vaccine being developed at Oxford suggest both that the vaccine is safe and that even the over-70s display a strong immune

response to it. Elderly people often respond poorly to vaccines, but in the Oxford case they were found to produce both antibody and T-cell immunity. The study, which has yet to be

published, was conducted on patients over 56 to test the vaccine’s impact on those most likely to develop serious Covid symptoms. Scientists were at pains to emphasise that it is too soon to

say for certain whether the vaccine protects against Covid-19, or indeed that it is safe for everyone. They will have to wait for results from much larger field trials to be confident. But

these results are undoubtedly encouraging. They hold out the prospect of an end to the nightmare of successive waves of Covid and prophylactic measures that do as much or more damage than

the disease. Too much should probably not be made of any one piece of academic research; after all, the pandemic has prompted many hundreds of studies all over the world. But the

implications for politicians who claim to be “following the science” are important. The Prime Minister has tried to steer a middle course between lockdown sceptics, mainly on his own

backbenches, who want to open up the economy and those such as the Labour Opposition or the Scottish and Welsh administrations who want to shut it down, albeit as a “circuit breaker”. This

week’s scientific evidence tends to support the Government’s _via media_ rather than either radical alternative. Most of England is still living under the relatively mild regime of Tiers 1

and 2; even Tier 3 is a long way short of full lockdown. He will get no credit for his moderation from those who are determined to paint him either as a Scrooge or as a Steerforth, but by

keeping restrictions on business and social life within bounds, Boris Johnson holds out some hope that the UK will end the year in better shape than was feared over the summer. There is even

the prospect that the nation may not spend  2021 engaged in damage limitation, but — with the help of an effective vaccine — be able to get the country back on track. This won’t exactly be

the most festive season we can remember. Still: with any luck we should have good reason to think of our glasses as half-full as we wish each other a (moderately) merry Christmas.