Antibody response to the SARS-CoV-2 virus wanes over time, latest research has suggested.
An ongoing study led by Imperial College London (ICL) found that the proportion of people testing positive for COVID-19 antibodies dropped by 26.5% over a 3-month period between June and September.
The findings from a non–peer reviewed preprint suggested that infection with SARS-CoV-2 confers only limited protection against reinfection.
Professor Paul Elliott, director of the REACT-2 programme at ICL, said: “Testing positive for antibodies does not mean you are immune to COVID-19.
“It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts.”
Experts said that, while the findings suggested that immunity might fade over time, the severity of illness from further infections could be reduced.
Antibody prevalence declined in all adults
Results from cross-sectional studies over the 3-month period involved 365,104 adults who self-administered a lateral flow immunoassay test.
There were 17,576 positive tests over the three rounds.
Antibody prevalence, adjusted for test characteristics and weighted to the adult population of England, declined from 6.0% to 4.4%, a reduction of 26.5% over the 3 months.
The decline was seen in all age groups. However, the lowest prevalence of a positive test, and the largest fall, was seen in those aged 75 years and older.
No change was seen in positive antibody tests in health care workers over the 3 months.
The results suggested that people who did not show symptoms of COVID-19 were more likely to lose detectable antibodies sooner than those who did show symptoms.
Prof Helen Ward, one of the lead authors of the report said that, while it was clear that the proportion of people with antibodies was falling over time, “We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes COVID-19, but it is essential that everyone continues to follow guidance to reduce the risk to themselves and others.”
Results ‘weaken argument for herd immunity’
Commenting on the results to the Science Media Centre, Rowland Kao, professor of veterinary epidemiology and data science at the University of Edinburgh, warned that, if the results were correct, “any strategy that relies on ‘herd immunity’ lacks credibility.”
However, he added that, “while the decline is substantial, nevertheless substantial proportions of the population do retain some immune response, over 4 months after the peak of the epidemic”.
Eleanor Riley, professor of immunology and infectious disease, also from the University of Edinburgh, said it was too early to assume that immunity to SARS-CoV-2 did not last because “the study does not look at antibody concentrations, antibody function, or other aspects of immunity such as T-cell immunity and does not look at the trajectory of antibody levels in the same individuals over time”.
However, she said the findings did not mean that a vaccine would be ineffective because vaccines contained adjuvants that could induce durable immune responses, particularly with multiple immunizations.
“What is not clear is how quickly antibody levels would rise again if a person encounters the SARS-CoV-2 virus a second time. It is possible they will still rapidly respond, and either have a milder illness, or remain protected through immune memory,” commented Dr. Alexander Edwards, associate professor in biomedical technology at the University of Reading.
Health Minister Lord Bethell said: “Regardless of the result of an antibody test, everyone must continue to comply with government guidelines including social distancing, self-isolating, and getting a test if you have symptoms, and always remember: hands, face, space.”
This article first appeared on Medscape.com.