As COVID-19 has spread around the globe, it appears that high transmission rates have been partly caused by a large number of people contracting the virus, who have no symptoms and then transmit it without knowing it.
Despite this, the screening of asymptomatic people to identify signs of infection has not been done much, due to the costs and limitations of testing capacity. Therefore, we have only a limited understanding of the role that asymptomatic people play in the spread of the disease.
We know that the production of protective antibodies following an infection forms the basis of immunity. But while it is clear that coronavirus infection results in the production of antibodies, we are not sure how much antibodies are produced, how long it lasts, or whether it protects people from getting the virus again.
Due to a lack of knowledge about these points, the researchers decided to test asymptomatic staff at Cardiff Metropolitan University in July 2020 for the presence of COVID-19 antibodies. Besides the fact that this study helped to find out how common asymptomatic infections were during the first wave, this showed more about how long COVID-19 antibodies can last and whether there are differences in how people’s immune systems respond to the virus. Here’s what the researchers found.
What the study showed
To run the screening program, they used a side-load “pregnancy” test strip that gave a result of a single drop of blood within ten minutes. These results were then compared with two independent methods used by public health laboratories to test COVID-19 antibodies. The study looked at the same people three months apart.
At the time of their first test in July 2020, all participants were feeling well, had not previously received a diagnosis of COVID-19, and had no obvious symptoms of the disease, although some reported mild symptoms of COVID in the past three months.
Of the 739 people examined, 3.65% had COVID-19 antibodies, which was slightly less than the national average suggested by the UK REACT study (4-6%) at that time. This is probably surprising, given that Cardiff is an urban area and therefore could be expected to have higher rates of infection.
The lower rate in this study could be explained by the fact that most university staff worked from home between March and September 2020 and were therefore largely protected from infections.
Men have more COVID-19 antibodies than women after asymptomatic infection
The study did not find a statistically significant difference in the number of men and women who had antibodies, although the prevalence of antibodies was highest in men over 40 years of age. A key difference: the levels of male participants were three times higher than those of female participants. This was despite the fact that there was no difference in previous COVID-related symptoms reported by men and women – suggesting no difference in the severity of infections.
When a second test followed three months later, another key difference was found. Of those who had previously had antibodies against COVID-19, 21.7% did not give positive results, which means that one in five asymptomatic people who generate antibodies against COVID-19 lose them after six months.
Interestingly, 80% of those who lost their antibodies in the study were women. Women who lost antibodies were also on average ten years older than women who retained antibodies. This may be related to an altered immune response in women who are approaching menopause or are post-menopausal, similar to that seen in the flu.
Overall, the results of the study suggest that as we assess immunity to COVID-19 – and its longevity – we need to be prepared for it not to be uniform. Age and gender could lead to significant differences.
–
