Immunity to coronavirus may only last for a few months after infection, according to new research findings that point to another obstacle to rolling out a vaccine.
The percentage of the UK population who have developed Covid antibodies had fallen by a more than a quarter since June to fewer than one in 20 people in the UK as of last month, the Imperial College London (ICL) study suggests.
The researchers say the “rapid” deterioration in immunity means that any successful vaccine may need to be administered twice a year unless the jab proves more powerful than natural immunity, The Telegraph reports.
The new research was commissioned by the Department of Health and was based on an analysis of home fingerprick test samples from 365,000 adults to establish “detectable antibody levels” over three months.
In June, shortly after the first coronavirus wave, 6% of the population had developed antibodies. But by September, the figure had fallen to 4.4%, “with most of the decline happening within just six weeks”, says The Telegraph.
The steepest fall “was seen in those most in need of protection”, adds the newspaper, with a 39% drop in people over the age of 75. The age group account for around three-quarters of Covid-related deaths in the UK.
By contrast, antibody levels fell by 15% among people aged between 18 and 24.
Professor Wendy Barclay, head of the Department of Infectious Disease at ICL, said the declines in antibody rates show that the UK is “miles off” achieving herd immunity.
“When you think that 95 out of 100 people are unlikely to be immune, and therefore likely to be susceptible, then we are a long, long way from anything resembling a population level protection against transmission,” said lead study researcher Helen Ward, a professor of public health.
Echoing that warning, fellow researcher Barclay cautioned that Covid herd immunity is unlikely to emerge and that the coronavirus is more likely to work like a common cold.
“Seasonal coronaviruses that circulate every winter and cause common colds can reinfect people after six to 12 months – and we suspect that the way that the body reacts to infection with this new coronavirus is rather similar to that,” she said.
“We don’t yet know what level of antibody is needed in a person’s blood to protect them from infection or reinfection,” added Barclay, but “most of the vaccine strategies are aiming to produce that level, and that level will feed into whether or not a population becomes immune or has any level of immunity”.
Barclay told The Guardian that the “results do not necessarily mean that immunity arising from vaccination would be short-lived”.
“A good vaccine may well be better than natural immunity,” she explained.
However, the results do suggest that the UK will have to wait for a vaccine before measures to control infections can be eased.
Graham Cooke, a professor of infectious diseases at ICL, said that “the need for a vaccine is still very large if you want to try and get a large level of protection in the population. People are starting to think about what we will need to do to boost vaccines periodically to keep levels of protection high.”
The ICL team point out that their study did not look into other forms of natural immunity. Several other research projects are currently examining whether T-cells, a type of white blood cell that forms part of the human immune system, could form part of a natural protection against the virus.
T-cells “thwart infections in two different ways”, says Science magazine: by encouraging other cells to produce antibodies and by destroying infected cells.
Some of this other research has “raised the possibility” that “T-cells, which can kill infected cells, or B memory cells, which can rapidly produce new antibodies”, may be another route towards gaining some protection against Covid, The Guardian reports.
However, the ICL scientists “said it is too soon to know if that is the case, or for how long that protection might last, while it is difficult to measure levels of such T-cells”, the paper adds.
“The fact that people get reinfected regularly throughout their lives with seasonal coronaviruses [that cause some common colds] suggests that the immunity, whether or not it is antibody mediated and/or T-cell mediated, probably isn’t very long-lasting,” said Barclay, who added that the team suspect the body reacts to infection with the new coronavirus in a similar way.
As research into immunity continues alongside the race to find a vaccine, study co-author Cooke says that adhering to Covid restrictions is the best line of defence for the time being.
“The big picture here is that after the first wave, still the great majority of the country didn’t have evidence of protective immunity,” he said.