After a difficult nine months, we are naturally all sick of lockdowns and other Covid restrictions. Everyone misses parts of their pre-coronavirus lives, from seeing friends and family, to pubs and restaurants, to the theatre and concerts and, yes, even our workplaces. It was therefore no surprise that this week’s news of a vaccine breakthrough was widely applauded. It is human nature, after all, to cling on to things that give us hope. Hope that was encouraged by leading scientists such as Sir John Bell. After the Pfizer news broke, the Oxford professor was asked on BBC radio whether we would be returning to normal by spring. His response? ‘Yes, yes, yes.’ This was a When Harry Met Sally moment that proved to be music to the ears of millions of Britons.

However, as a microbiologist who has worked on vaccine discovery, I struggle to see how, despite this very welcome leap, we can possibly be back to normal by spring.

For starters, what quantity of vaccine is needed to return life to normal? Well, ‘we don’t know’, according to Matt Hancock. He is right to be cautious, because we still don’t know how effective the vaccine will be for its initial target demographic: care-home residents and staff. All we know so far is that it can protect some people for seven days after the second ‘shot’. There is no evidence yet of long-term immunity.

It is unlikely to fall at the safety hurdle, but there are major questions over how it will be delivered. We need to be ready for the very real possibility that it could throw up surprises, such as how it might be tolerated by the elderly. Because this particular type of vaccine (of which we know relatively little) has never been licensed before, we cannot simply assume it will be ready to be rolled out in a matter of weeks, as is being breathlessly reported in much of the media. The challenges that will shortly become apparent won’t be insurmountable, but they will be time-consuming and will very probably slow the rollout.

There is a strand of wishful thinking that coronavirus is an issue only for the old. The refrain that we can ‘shield those at risk and return to our normal lives’ will only get louder as we approach the Christmas season. But even if we vaccinate the elderly in care homes, the stark fact remains that millions of us remain at risk. Just look at the data on those who died in April: proportionately, the death of someone in England and Wales in the 45-64 age group is more likely to be due to Covid-19 than the death of someone aged 85 and over.

In the UK, more than half a million of us have undiagnosed diabetes and five million are unaware of our high blood pressure. Why does this matter? Because these significantly elevate the risk of complications if you catch Covid-19. We also have a considerable overweight population, many of whom suffer from both aforementioned conditions: some 63 per cent of our adult population are believed to be overweight. Boris Johnson, for instance, pointed to his weight as a factor in his near-death experience with the virus. (‘Don’t be a fatty in your fifties,’ he warned.)

To be blunt: walking among us are millions of working-age adults, living productive lives, who are at real risk from Covid-19. The Office for National Statistics calculated that in England and Wales when the epidemic was gathering momentum from late February to lockdown on 23 March, the coronavirus infected 3,839 working-age adults whom it then killed in the weeks that followed.

A sizable number of Britons are inclined to reject any vaccine when it is ready to be fully rolled out. Talk of speedy development unnerves some people, while others believe it is pointless because the virus does not threaten them. One study from King’s College London this summer showed that only 53 per cent of Britons would be ‘certain’ or ‘very likely’ to get vaccinated.

Pfizer’s press release states the vaccine leads to a 90 per cent reduction in the disease. Another big question remains unanswered: does the vaccine stop you becoming infected by the virus in the first place or just from becoming sick when you do? The former is needed to confer herd immunity, something particularly useful to care-home and healthcare workers, as it would prevent them from passing on the virus to those they care for. But if it just represses symptoms, there will be no protection for other people. It is worth remembering that in the Oxford trials, they found that in monkeys the vaccine only elicited protection against the symptoms, as opposed to stopping asymptomatic carriage of the virus.

Vaccine trials can — and regularly do — fall at the final fence. I once worked on a project to identify potential vaccines for the MRSA ‘superbug’. A major pharmaceutical company took forward one of the candidates and it all went well until it was discovered that the vaccine (which had been intended to reduce the risk of post-surgical infection) increased the likelihood of death by a factor of five. It should not be forgotten that no Covid vaccine has actually completed its trials yet, let alone provided any data on longevity of protection.

Of course the Pfizer vaccine is a big conceptual leap and it should be applauded. We now know that it is possible to generate protection against Covid-19. Given the scale of economic damage wrought by this disease, that’s been humanity’s biggest endeavour for the best part of a year; at no point was it ever a certainty. But we must not kid ourselves into thinking that it is a short-term silver bullet and life will return to normal any day now. We will probably need to maintain social distancing and mask-wearing, and carry out mass testing, for much of next year. The vaccine announcement is good news, but we must not blow it out of proportion. We are still some distance away from the end of this crisis.