The findings from a surveillance study of 365,000 people raise a terrifying prospect – one of Britain as some sort of Narnia, where it is always winter but never Christmas.
Research by Imperial College London has been key to Government policy-making on the pandemic from the off. Most famously, it was behind the modelling that persuaded Boris Johnson to order the country into full lockdown in March.
The study being published now is no less significant.
For months, the Government's approach to the pandemic has been predicated on the assumption that a vaccine will ultimately come to the rescue.
Until then, measures can only "buy time". If successful, restrictions on liberty can push down the 'R' rate, reducing levels of infection, saving lives and preventing the NHS from becoming overwhelmed.
All of this is, of course, a short-term measure with colossal costs, not just to the economy but also in lives lost from diseases other than Covid-19.
Falling antibody rates
But the research suggests a still more fatal flaw in the strategy – that such policies could be counting on a breakthrough that may never come.
Imperial's scientists analysed the results of finger prick tests on hundreds of thousands of people to establish antibody levels in communities across England between late June and September.
They found that across the country, antibody prevalence – which only reached six per cent in June – than saw a significant decline. Overall, it fell to 4.4 per cent within three months, a fall of more than one quarter.
However, scientists are wrestling with major uncertainties when it comes to Covid-19. An antibody response suggests some protection against future disease, but no one knows how much.
The purpose of vaccines is to create this response in those who have not been infected with Covid-19, thus creating herd immunity.
If such protection only lasts a matter of weeks, or months, how effective could any vaccine be? And would it have to be administered so often that the scale of the challenge defeats us?
Here, yet more unknowns come into play. Scientists do not know what level of antibody response is required to protect against Covid-19.
Low levels, perhaps even undetectable by current testing, could be enough to offer some protection.
Antibodies are not the body's only defence. There is significant interest in the part played by T-cells, a type of white blood cell that helps the immune system fight off viruses, which some believe may be even more important in fighting off Covid.
Such an immune response has been linked to previous exposure to common cold coronaviruses, and could explain why children are more resilient to Covid-19.
We need a vaccine
Researchers behind the study say that, in fact, their findings underline the need for an effective vaccine. They point out that a vaccine may prove far more powerful than any natural immunity.
While Covid-19 is the only coronavirus to have become a household name, scientists have a long history of other types of coronaviruses, most notably the common cold. This leads them to believe it is likely that the virus could reinfect people every six to 12 months, which could mean a vaccine programme would have to be boosted very regularly.
The hope is that an effective vaccine would be strong enough that it could be administered annually, like a flu jab. If it needs to be given more often than that, the logistical hurdles ahead get still more difficult.
Monday's findings will give the Government a new set of questions, headaches, and trade-offs to consider. And they are likely to be used to support a range of arguments, many of which are in conflict.
Some will say they show the hopelessness of efforts to contain Covid-19, raising the prospect of interminable restrictions which are unsustainable.
Others will say they demonstrate the need for still more strict restrictions, while every effort is thrown into the development and mass rollout of a vaccine. The chance of the Government allowing "immunity passports" for those who have a positive antibody test appears ever more remote.
And the chance of the development of policies which rest on natural herd immunity looks slimmer still.