Covid-19 antibody response wanes over time: UK study

The antibody response to Covid-19 virus wanes over time, said a new analysis released on Tuesday based on finger-prick tests on more than 365,000 randomly selected people in England.

The tests carried out at home between June 20 and September 28 found that the number of people testing positive dropped by 26.5% across the study period, said the researchers led by Imperial College London.

The downward trend was observed in all areas and age groups, but not in health workers, which could indicate repeated or higher initial exposure to the virus, the authors suggested.

The decline was largest in people aged 75 and above compared to younger people, and also in people with suspected rather than confirmed infection, indicating that the antibody response varies by age and with the severity of illness, the college said.

Paul Elliott, director of the programme at Imperial College, said: “Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies. 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. If someone tests positive for antibodies, they still need to follow national guidelines including social distancing measures, getting a swab test if they have symptoms and wearing face coverings where required,” he added.

The study used finger-prick testing to detect coronavirus antibodies in the blood. When present, they indicate that a person has been previously infected with the virus. The testing kits, called Lateral Flow Tests, detect antibodies above a particular concentration in the blood, and do not measure the amount of antibodies in a particular person.

The conclusions include findings from three rounds of testing carried out over a three-month period. There were 17,576 positive results across all three rounds, around 30% of whom did not report any symptoms.

After accounting for the accuracy of the test, confirmed by laboratory evaluation, and England’s population characteristics, the study found that antibody prevalence declined from 6.0% to 4.8% and then 4.4% over the three months.

This was found across all ages but the smallest drop was found in the youngest age group, aged 18-24, falling from 7.9% to 6.7% (14.9%, while the largest was found in the oldest group, aged 75 and above, declining from 3.3% to 2.0% (39%.

Helen Ward, one of the lead authors of the research report, said: “This very large study has shown that the proportion of people with detectable antibodies is 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.”

Covid-19 antibody response wanes over time: UK study