The third and final round of a coronavirus prevalence study has confirmed that 5.2% of residents of Spain have developed antibodies for the virus. But according to the results of the survey, which was presented on Monday by the Spanish Health Ministry, not all sectors of the population have been affected in the same way depending on their occupation.
Ten percent of healthcare workers, for example, tested positive for antibodies, while police and fire crews also saw higher than average incidences, with 6.3%. Employees of senior residences – which have been a focal point of the pandemic in Spain – registered a 7% rate of antibodies.
The prevalence study was carried out to determine how many people in Spain have developed antibodies after exposure to the virus. The eight-week study was conducted by the Carlos III public health institute, which took blood samples from nearly 70,000 participants.
According to the results of the third and final round, only four provinces in Spain have prevalence rates above 10%: Soria (14.4%), Segovia (12.4%), Madrid (11.7%) Cuenca (11.4%) and Albacete (10.8%).
On the other end of the spectrum, the North African exclave cities of Ceuta and Murcia, as well as the regions of Asturias, Galicia, the Balearic Islands and the Canary Islands, reported prevalence levels equal to or below 2%.
These numbers indicate how many people have IgG antibodies, which take longer to show up in the body and which mean that the person has been exposed to the virus but does not have an active infection. The serology test also detects IgM antibodies, made earlier by the immune system in response to the virus – around six to seven days after the onset of symptoms.
The Spanish overall figure of 5% is in line with studies in other European countries that showed a prevalence of 4% to 5%, far below the rate that would provide the population with so-called herd immunity, and which experts place at 60% at the very least.
The director of the Carlos III institute, Raquel Yotti, and the general secretary of the Health Ministry, Faustino Blanco, called for the population of Spain to not lower its guard, given that 95% of the population is still vulnerable. “We cannot relax,” said Yotti, adding that there is still a lot of uncertainty as to the protection that having antibodies offers to someone who has been infected. In fact, the survey revealed that between the first and second wave of testing, 7% of subjects no longer tested positive for antibodies. Between the first and the third, this rate rose to 14%.
“Not being able to detect antibodies does not mean that these people are not immunologically protected,” explained the director of Spain’s National Epidemiological Center, Marina Pollán, given that people can also have cellular immunity, something that has not yet been so closely studied in this coronavirus. Serological tests detect the production of antibodies, but not cellular immunity, which could explain why people who have tested positive in a PCR test (which detects an active infection) then later test negative in antibody tests.
The results of the final round of testing showed that there was no significant difference in how the coronavirus affects men and women, or people of different nationalities. Children reported the lowest prevalence levels in the first round of testing, but these differences were less evident in the final wave.
Education level, disabilities and the number of people in a household were also not found to have any bearing on antibody levels.