I was invited to a dinner party a week ago. The host was an old friend, now a senior doctor at a busy London hospital. When this pandemic started, he feared the worst. Though he didn’t say so, he thought his own number might be up. Over the next few weeks, as he and his colleagues battled to save lives, the surge in admissions threatened to overwhelm his hospital’s critical care units. By early April, fears of the virus were so intense that some victims were dying in isolation. Staff lent mobile phones to patients on their deathbeds, so they could say goodbye to people they loved.

Last weekend couldn’t have felt more different. As we traded lockdown tales in the garden – a conversational bargain, from my point of view – it became almost possible to forget that a cataclysm’s still in progress. And when I wondered what the coronavirus was going to do next, my friend, who always seems pretty buoyant, looked elated. He’s recently had an antibody test, and though he doesn’t recall suffering any illness worse than a chill this year, it showed he’d had COVID-19. As if astonishing himself, he held out clenched fists and opened them slowly. ‘Obviously it’s not just me’, he said. ‘Who knows exactly what it means? But in London, I’m pretty sure herd immunity’s been achieved.’

That says a lot more about my friend’s confidence than demonstrable reality. Though government serology testing suggests that at least 17% of the capital’s residents had COVID-19 antibodies by mid May (compared to 5% elsewhere), it’s not clear yet how – or if – they protect against re-infection. Insofar as there might be heightened resistance in London, it’s certainly not total. But the exchange got me recalling how contentious the hope for universal immunity has become – and how weird that is.

The controversies began with an appearance by Boris Johnson on ITV’s This Morning on 5 March. The prime minister told Holly and Phil that all the scientists he was talking to were ‘brilliant’, and that one of their many clever suggestions was that the population could maximise its resistance to COVID-19 by ‘taking it on the chin’. That was enough to convince some critics that the Tories were cooking up a plan to cull the weak and murder the old. But in the uneasy, apprehensive days of early March, a more common reaction was stunned surprise. A prime minister who’d built his career on levity was wondering whether the best way of tackling a lethal pathogen might be to spread it around. Many foreigners were just amazed, unsure if Britain under Bojo was more sacrificial or suicidal. My favourite response was a popular joke on the Chinese social media site Weibo: ‘After leaving Europe, they now want to leave the world.’

I was definitely among the stunned. Call me an apologist for genocide, but the hidden agenda struck me even then as more panic-stricken than sinister. Ministers and advisers weren’t being ruthless; they were in disarray. When Johnson took control of pandemic management at a COBRA meeting on 2 March – after delegating the job to Health Secretary Matt Hancock for a month – his priority was apparently to cling to boffins: claims to be ‘guided by the science’ quickly become a mantra among ministers. And though the government’s chief scientific adviser Patrick Vallance said on 13 March that ‘herd immunity’ was one of ‘our aims’, the prime minister promptly lurched in favour of a strict lockdown – again, ‘on scientific advice’ – after a team of Imperial College epidemiologists under Professor Neil Ferguson published an urgent forecast. It warned that a failure to check COVID-19 would probably lead to hundreds of thousands of deaths.

That’s all history (except insofar as the machinations will one day be evidence in an inquiry) but neither the science nor the politics is settled. Ferguson proposed last week that locking down a week earlier would have halved this country’s death toll. The Swedish scientist most closely associated with an alternative policy, who advised his government to go easy on restrictions, has just said that in hindsight he’d have favoured stricter measures. Neither Patrick Vallance nor the government’s chief medical officer, Chris Whitty, are prepared to admit past mistakes, but both insisted on Wednesday that they were monitoring events carefully, because we’re ‘not at the end of this pandemic, not by a long shot’. And with shops and zoos preparing to open, school gates staying closed, and political protests multiplying, there’ll be plenty of events to monitor. While the scientists gather data, we’re living the experiment.

And even if government interventions should have been earlier or firmer, an alternative argument remains strong. In the absence of a vaccine, widespread immunity offers many countries their best hope of getting through this pandemic. Though right-wing extremists like Brazilian president Jair Bolsonaro have yoked cynical political agendas to this claim, credible science also justifies it. The reasoning has been vocalised best by an academic who co-authored a paper published at Oxford University a week after Ferguson’s Imperial report. Professor Sunetra Gupta maintains that at least half the British population are already immune to COVID-19, and that the coronavirus is ‘on the way out’. Natural resistance or antibody acquisition explains why the disease has ‘grown, turned around and died away’ all over the world, ‘almost like clockwork’.

Gupta isn’t a fascist any more than Neil Ferguson is a snowflake. She objects to the ‘libertarian harangue’ that’s been ‘hitched’ to the scientific modelling of her Oxford team, she firmly supports enhanced protection for vulnerable people, and (as befits a scientist who’s also a prize-winning novelist) her stance is both nuanced and empathetic. Lockdowns aren’t just hindering the acquisition of immunity, in her view. ‘The truth is that lockdown is a luxury. And it’s a luxury that the middle classes are enjoying, and higher income countries are enjoying, at the expense of the poor, the vulnerable and less developed countries. To think of it simply in terms of “is this epidemic going to be over or not?” is really unconscionable.’ Personal factors might also explain her differences with Imperial – but if they do, Gupta isn’t entirely at fault. Her career was almost nobbled by false allegations in 1999 that she was sleeping her way up the career ladder – and though the man who slandered her duly lost his Oxford professorship, Roy Anderson took a team of 70 loyal epidemiologists with him to Imperial College. One of them was Neil Ferguson, who relied directly on a recent Lancet article by Anderson for the structure of the Imperial lockdown paper.

Scientists’ likeability and their rivalries don’t say much about the reliability of any particular piece of work, but the contrasting approaches of the Imperial and Oxford analyses still illustrate an important truth. Data is meaningless until it’s interpreted, and no one yet knows which interpretations of COVID-19’s spread are going to end up most accurate. Every epidemiological model in use at the moment draws heavily on what happened during the Spanish Flu pandemic a century ago (Neil Ferguson, like Anthony Fauci in the United States, has written influentially about what it might teach), but history only offers signposts. Though social distancing, school closures and the prevention of mass gatherings reduced fatalities back then, many deaths were delayed by months, not staved off for years – and that’s bound to be even truer of a coronavirus that disproportionately hits the old and sick. Spanish Flu also mutated far faster than COVID-19, and its vicious second spike can’t say much about what recurrent waves of infections will do today. In any event, lowering casualties by slowing down the world threatens collateral damage that’s simply unknowable. According to one guesstimate, global lockdowns could cause 1.4 million extra deaths before 2025 from tuberculosis alone.

No one’s necessarily to blame if epidemiological guidance turns out to be wrong: science does that sometimes, and politicians are elected to decide between options and put advice into practice. But judgments aren’t immune from criticism either – and even as I’ve been writing this post, a strategy to pretend otherwise has been on show. At last Wednesday’s Downing Street press briefing, Patrick Vallance and Chris Whitty flanked the prime minister, and all three batted away journalists’ questions about whether they had made any mistakes. The scientists said it was too early to know, while Johnson deferred to their expertise. It was a smooth circle of excuses, for fixed decisions with final consequences. Key workers and health professionals were lethally under-supplied when they needed protective equipment most. Broken promises to ‘cocoon’ and ‘shield’ the vulnerable contributed to a care home catastrophe and a per capita death rate that might well end up the highest in the world. Though everyone’s able to shift responsibility for now, there’ll come a time when the political buck won’t be as easy to pass around . . .

Along with quite a few people I know, I’m vacillating between optimism and despondency at the moment, and last week’s dinner party kept me teetering. My upbeat friend was echoing hopes I share, but the risks from COVID-19 still feel very real. Holding back from an instinctive hug and handshake, he was entirely sympathetic. ‘You’re sensible’, he nodded. ‘That’s wise. Completely understandable. You’ve got mild panphobia.’ That came as news to me, and I turned over the diagnosis in my mouth as I cycled homewards. When I reached Battersea Bridge, curiosity got the better of me. Pausing to look at the river and absorb the nocturnal hush that’ll soon become unimaginable again, I keyed ‘panphobia’ into my phone. It turned out I’d been displaying symptoms of an ‘abnormal, vague, persistent dread of everything’. That sounded about right. But as I wobbled on, a tinge of irrational exuberance was added to the dread. Doctors know their stuff. Perhaps antibodies really are widespread? Even I might have picked up a few. I definitely remember a cough in February.