ge brings few benefits, as far as I can see: not wisdom, not virtue, nor serenity. But what a bonus to find yourself among the ranks of septuagenarians lining up for the Covid-19 vaccine. This gift of life arrives via an automated NHS text message, amid the hospital horror-show of the TV news. Whoops of relief spread among senior friends who are due for the jab shortly: how sublimely lucky, how good to be old, as the angel of death passes over. “Cry freedom!” said the health secretary, Matt Hancock, wooing Spectator-reading libertarians with a promise of imminent release from lockdown, once society’s most vulnerable people have been vaccinated. He’s overpromising yet again, and it’s not the official message: even Boris Johnson has managed to warn that there will be no “open sesame with a big bang”. The message for vaccinated people is to change nothing: stay home, mask up, no travel, no indoor meetings beyond your household, obey lockdown rules. No one can be 100% sure you might not still contract it, or more likely, you might not still unknowingly spread it. So there will be no oldies’ raves, at which they flaunt their privileged vaccine freedom. That’s a good, simple public health message, one that’s easy to communicate – or it would be if all messaging hadn’t been crippled by 64 different changes to science-ignoring rules imposed too late and Dominic Cummings’ eyesight test. But what about the sudden decision to offer just one dose, with a second 12 weeks later (probably)? Immunologists describe their visceral shock when the one-dose edict came down out of the blue from the chief medical officers and the Joint Committee on Vaccination and Immunisation. Prof Deborah Dunn-Walters, chair of the British Society of Immunology’s expert advisory panel on Covid-19, says her committee was stunned: “As scientists we felt offended: after gazillions had been spent on vaccine trials, why throw it all away?” These scientists balked at approving a single dose without thorough trials and peer-reviewed results – and some still privately object. But in this deadly emergency, “I said we just have to get over ourselves” and by a narrow margin, the committee agreed to back the single dose. The government’s official pronouncement sounds rather more scientifically fire-proof: “Short-term vaccine efficacy from the first dose of the Pfizer-BioNTech vaccine is calculated at around 90%. Short-term vaccine efficacy from the first dose of the AstraZeneca vaccine is calculated at around 70%, with high protection against severe disease.” But here’s the kicker, an essentially political, pragmatic, even moral decision: “Given the high level of protection afforded by the first dose, models suggest that initially vaccinating a greater number of people with a single dose will prevent more deaths and hospitalisations than vaccinating a smaller number of people with two doses.” That makes good sense to me. With deaths soaring again to new highs, priority goes to staunching the flow of older and vulnerable people into overflowing hospital ICU units with shattered NHS staff. Early rationing might have prioritised all essential workers – NHS, teachers, supermarket staff, post and delivery drivers and so on. The over-70s are rarely essential (except Joe Biden, 78). But that would have caused the NHS to collapse, unless all over-70s were denied hospital beds and left to die gasping for air, a horror from which society and the NHS would never recover. As it is, there will be inquests into why care home deaths are rapidly rising again, as the government fails to vaccinate half of them. Surely, they should be easy enough people to find and jab. However, the official public health messaging is contradictory. Even the obedient among those who have been newly vaccinated will ponder why, if a single dose is so effective, they can’t sneak out and visit other vaccinated or post-Covid family and friends. Professor Dunn-Walters tells me she is unaware of reports of hospitalisation from Covid in people who have received a single dose of the vaccine: she expects that any subsequent infections would likely be mild. Yes, that risk of infection and transmission is there – the vaccine isn’t a guarantee against either. And some might have been alarmed at the new Israeli evidence this week showing thousands of single-dosers had become infected. It is perhaps too early to draw conclusions. But Dunn-Walters seems sanguine, suggesting that many in Israel could have had it already when injected, or might have gone out and mixed with people before waiting for the vaccine to begin to take effect over three weeks. Perhaps those people hadn’t been told about that absolutely crucial three-week isolation time: no one in Britain is handed that information in the leaflet given out with the vaccination. Why not? “The public health message is that everyone has to behave exactly the same as before, no change,” she says. The fear is that people who are over-confident after being vaccinated will behave like the Israelis may have: even if they don’t catch it themselves they could be spreaders – and above all, they will change the culture. Seeing gangs of old people doing the wrong thing would break the communal endeavour to stay home, and younger people would rebel. Off the record, some immunologists say all the facts should always be given out. One tells me, “I couldn’t possibly say it in public, but yes, all public health messages should be honest or eventually none of them will be believed.” Besides, the facts may change with some frightening new variant. The problem for public health messaging is that some people never hear it: maybe a quarter never hear or read what Guardian readers might recognise as news, relying on family and friends. So only shouting loud, clear and simple messages will ever reach enough of the population to establish a Covid-safe norm. But vaccinated older people ought to observe the precautionary principle when much is unknown. And they had better behave themselves, in gratitude for this life-saver. Polly Toynbee is a Guardian columnist