Date Published: 06/07/2020
ARCHIVED - Spanish study suggests immunity against covid diminishes with time
ARCHIVED ARTICLE
14% of those tested had lost covid antibodies after six weeks, ruling out the possibility of herd immunity
On Monday Dr. Marina Pollán, director of the National Center for Epidemiology in Spain, presented study data which confirms that only 5.2% of the Spanish population has developed antibodies against the covid virus, the same result as in the second study carried out before the state of emergency concluded.
Doubts about the duration of immunity against the coronavirus persist and have in fact increased after data from the third round of the seroprevalence study carried out by the Ministry of Health was processed, indicating that 14.4% of the cases that tested positive in the first round no longer had detectable antibodies six weeks later.
"Not having antibodies does not mean that these people are not immunologically protected," said Pollán, who admitted that "the tools we are using to detect antibodies are not perfect."
54,858 indivisuals from across Spain participated in the three stages of the study, with 186,908 rapid tests carried out (plus 9,755 in an island-specific study) and 165,176 blood samples were collected. In addition, more than 62,000 people were monitored telephonically during the study.
Seronegativization - the loss of antibodies after testing positive in previous weeks - was more frequent in asymptomatic people (those who didn´t actually show any symptoms but tested positive) and much less frequent in participants with a positive CRP ( C-reactive protein (CRP) is a blood test marker for inflammation in the body. CRP is produced in the liver and its level is measured by testing the blood. CRP is classified as an acute phase reactant, which means that its levels will rise in response to inflammation) and in those who described a sudden loss of smell or taste, according to the study.
Raquel Yotti, director of the Carlos III Health Institute, says that the results are a "warning message" to those who have contracted the virus and believe that they now have immunity so no longer have to follow health recommendations and observe social distancing.
"The data highlights this uncertainty. I want to send a message of warning to those people who have overcome the virus and who may think they already have full immunity," she said.
A study developed by researchers from the Chongqing University of Medicine and recently published in Nature Medicine reinforced this argument by concluding that the antibodies generated naturally by the body against Covid-19 begin to decrease two to three months after contagion.
Dr. Pollán stressed that not having detectable antibodies was not synonymous with not having immunity to the coronavirus, given that "we know of diseases such as hepatitis in which the antibodies disappear but the cells that produce these antibodies have an immunological memory."
Otherwise, the data from the third round of the study confirms the results of the previous two sets of data, ruling out the possibility that natural group immunity (herd immunity) may be effective long-term in overcoming the pandemic, the principal conclusion being that 5.2% of the population has been infected with Covid-19.
In conclusion the report states; "The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas. Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic. These results emphasise the need for maintaining public health measures to avoid a new epidemic wave".
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