Medical staff push a patient on a gurney to a waiting helicopter in France, to be evacuated on another hospital. AFP
In the first study of its kind, a team led by researchers from King's College London examined the levels of antibodies in more than 90 confirmed virus patients and how they changed over time.
Blood tests showed even individuals with only mild COVID-19 symptoms mounted some immune response to the virus.
Of the study group, 60 per cent showed a "potent" viral response in the first few weeks after infection.
However, after three months only 16.7 per cent had maintained high levels of COVID-19-neutralising antibodies, and after 90 days several patients had no detectable antibodies in their bloodstream.
When the body encounters an external danger such as a virus, it mobilises cells to track down and kill the culprit.
As it does so, it produces proteins known as antibodies that are programmed to target the specific antigen the body is fighting, like a key cut for a particular lock.
As long as someone has enough antibodies, they will be able to snub out new infections, giving them immunity.
But Monday's research suggests immunity cannot be taken for granted and may not last more than a few months, as is true with other viruses such as influenza.
Playing the lottery
Experts said the findings may change how governments plan for the next phase of the pandemic, including how they fund and organise vaccine research and development.
"This is an important study that starts to define the longer-term dynamics of the antibody response to SARS-CoV-2," said Lawrence Young, professor of Molecular Oncology at the University of Warwick, using the full name of the virus strain.
"It further emphasises the need for us to better understand what a protective immune response looks like if we are to develop an effective vaccine," said Young, who was not involved in the research.
James Gill, an honorary Clinical Lecturer at Warwick Medical School, said the research reiterated the need for everyone to continue taking measures to mitigate the virus spreading, particularly at the start of Europe's holiday season.
"In the same way that these patients were surprised to have antibodies to COVID19, we should NOT be surprised if any protective benefit is mild, or at least transient," he said.
"If you played the lottery and won £10, you wouldn't immediately think that you had acquired increased natural luck, and used your life savings to buy further lottery tickets.
"Even those with a positive antibody test — especially those who cannot account for where they may have been exposed — should continue to use caution, social distancing and appropriate mask use."
Women took to the streets in peaceful democracies and in countries gripped by conflict, though in far smaller numbers than last year, when the full force of the COVID-19 pandemic had yet to hit the world.
Like millions of other Britons, the prime minister will be able to have a trim and a tipple on Saturday, when the country takes its biggest step yet out of coronavirus lockdown with the reopening in England of restaurants, pubs and hairdressers, along with secular and sacred venues including cinemas and church.
The contrasting situation in Europe was highlighted on Monday when the EU Commission proposed that travellers who are fully vaccinated with EU-approved jabs be able once again to enter the bloc, if they come from countries keeping COVID-19 at bay.
It is the latest grim milestone after the novel coronavirus surfaced in central China in December 2019 and went on to infect more than 139 million people, leaving billions more under crippling lockdowns and ravaging the global economy.
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