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Hopes that the population will become immune to COVID-19 have been dashed by new research showing that antibodies decline rapidly after recovering from the disease.
So-called group immunity has been proposed by some scientists as a better alternative to blockages to address the coronavirus pandemic.
Around 50-60% of the population would be required to have protection against the virus so that it could no longer transmit efficiently.
The number of people with antibodies decreased since the blocking measures were eased
However, a major UK study has found that instead of developing immunity over time, the number of people with antibodies has dropped by 26% since the blockage eased over the summer.
Researchers from Imperial College London examined 365,000 people during three rounds of tests between June and September.
Results from the REACT-2 study showed that 6% of people had antibodies to the virus at the time the blockage was relieved in late June and early July.
But at the start of the second wave last month, this fell to just 4.4%.
Professor Helen Ward, one of the researchers, said the new results strongly suggest that herd immunity is unattainable.
“When you think that 95 out of 100 people are likely to remain susceptible, we are very, very far from anything that looks like protection at the population level against progressive transmission,” he said.
“It’s not something you can use as an infection control strategy [for COVID-19] in the population “.
New research suggests that herd immunity cannot be achieved
The finding is another blow to the scientists behind the controversial Great Barrington Declaration, who suggested that vulnerable people could protect themselves at home while the virus spreads through the young and healthy to build herd immunity.
The proposal has been heavily criticized by many other scientists.
The researchers found that younger people, those from Black, Asian and Ethnic Minority Communities (BAME), and healthcare workers had higher levels of antibodies, possibly because they were in regular contact with infected people.
The drop in antibodies suggests that people will be re-infected regularly, as with related coronaviruses that cause the common cold.
Professor Wendy Barclay, an infectious disease specialist and one of the researchers, said antibodies peak three to four weeks after symptoms and then disappear, as do related viruses.
She said: “Seasonal coronaviruses that circulate each winter and cause common colds can re-infect people after six to 12 months.
“We suspect that the way the body reacts to infection with this new coronavirus is similar.”
So far there have only been a handful of documented cases of reinfection.
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Dr Alexander Edwards, associate professor of biomedical technology at the University of Reading, said: “What is not clear is how quickly antibody levels would rise if a person were to encounter the virus a second time.
“They may still respond quickly and have milder disease or remain protected through immune memory.
“So even if the rapid antibody test is no longer positive, the person may still be protected against reinfection.”
The study, which has not yet been peer-reviewed, only measured antibodies.
Another arm of the immune system, called T cells, may remain active, but there is currently no test available for them.
Scientists are cautious about using the results to predict the protection a vaccine provides.
They say that immunizations can lead to a stronger antibody response.
Health Minister Lord Bethell said the study “is a critical piece of research, helping us understand the nature of COVID-19 antibodies over time and improving our understanding of the virus itself.”
He added: “We rely on this kind of important research to inform our continued response to disease so that we can continue to take the right action at the right time.
“It’s also important for everyone to know what this means to them – this study will help in our fight against the virus, but testing positive for antibodies does not mean that you are immune to COVID-19.”
