5.2% of residents in Spain have developed antibodies for the coronavirus after the last round of a nationwide study. The presence of antibodies does not mean that the people are immune to Coronavirus.
An eight-week study was carried out by the Carlos III Public Health Institute to determine how many people in Spain developed antibodies after being exposed to the coronavirus. The final round of this coronavirus prevalence study revealed that only 5.2% of Spain’s residents have developed antibodies for the coronavirus (or SARS-CoV-2).
Spain has been one of the hardest-hit European countries by the pandemic. This finding strikes people around the world, who believe that antibodies throughout populations could provide group protection against the coronavirus, a phenomenon called herd immunity. Given the often asymptomatic nature of this virus and limited diagnostic tests, this study reveals the extent of the COVID-19 epidemic by detecting antibodies.
The study published in the Lancet journal says, “at least a third of infections determined by serology were asymptomatic.”
Design of Study
The Seroepidemiological Survey of SARS-CoV-2 Virus Infection in Spain (Encuesta Seroepidemiológica de la Infección por el Virus SARS-CoV-2 en España; ENE-COVID) was a nationwide population-based study. The first round was conducted from April 27 to May 11, 2020, and each round of testing took two weeks. In participants, the serum sample was collected every 2 to 4 weeks apart.
About 70,000 participants took serology tests, a blood test that detects microorganisms like the coronavirus. While the confirmation of IgG antibodies would indicate that “the person has been exposed [to the coronavirus] but does not have an active infection,” the detection of IgM antibodies confirms an active infection. IgM antibodies are formed by the immune system in response to the virus and are detectable in the blood around six to seven days after the onset of coronavirus symptoms.
This study’s statistical design is carefully representative of Spain’s residents. The published investigation says, “A key strength of our study is the random selection of households from the national municipal register (updated on January 1, 2020), which allowed us to contact a representative sample of the non-institutionalized Spanish population.”
This decision to collect a representative sample came hand-in-hand with disadvantages and extra effort. The study explained, “Young adults have proven to be more difficult to find, probably due to their higher mobility, with many of them officially registered at their parents’ home but living elsewhere. Also, some potential participants were staying at their second residences, leaving an empty house whose members could not be included.”
Additionally, the household selection excluded nursing home residents who could account for around 6% of Spaniards older than 75 years, according to the study. However, this investigation took that demographic into consideration as well.
It elucidated, “Even though care homes have been a hotspot of infection and death in the country, most Spanish elders reside in households, and they are adequately represented in our study.”
Why do we test for antibodies?
Antigens are things that cause an immune response in the body, including viruses such as the coronavirus. In response to the unwanted antigen, large Y-shaped proteins develop to neutralize the virus and counteract it. Their shape supports their function as they have two antigen-binding sites. These proteins are called antibodies, or specifically immunoglobulin (or Ig).
Antibodies form an essential line of defense and may offer protection against the novel coronavirus. Immunoglobulin G, or IgG, is the most common type of antibody circulating in our blood. Immunoglobulin M, or IgM, is the first antibody that forms in response to an antigen. Vaccines take advantage of this immune response and produce antibodies that recognize the vaccine’s antigen at their next encounter.
The use of two IgG antibody tests aimed at different SARS-CoV-2 antigens allows us to specify a range of seroprevalence between 3·7% and 6·2%, depending on whether we favour greater specificity (ie, a positive result in both tests), which might be preferred when prevalence is low,20 or greater sensitivity (ie, a positive result in either test).
Results of Study by Regions in Spain
The Spain peninsula is right above the North African countries, Morocco and Algeria. In epidemiology, prevalence is the proportion of a given population that has been affected by a medical condition. In this study, called Prevalence of SARS-CoV-2 in Spain: a nationwide, population-based seroepidemiological study, prevalence refers to how many people developed IgG antibodies after being exposed to the coronavirus. The more, the better.
Just South from Spain, the North African exclave cities, Ceuta and Murcia, including the regions of Asturias, Galicia, the Balearic Islands, and the Canary Islands, had minimal prevalence levels of 2% or less.
In Spain, the first round of testing was conducted during the lockdown.
In the first and second waves of testing, 5% of citizens had contracted the virus, and 5.2% had recovered from it. In the third and final round, four provinces in Spain had prevalence levels above 10%. The results showed: Soria (14.4%), Segovia (12.4%), Madrid (11.7%) Cuenca (11.4%) and Albacete (10.8%).
Herd Immunity Is Not Attainable
Spain’s nationwide prevalence of 5% positive antibody tests is similar to that of other European countries, 4-5%. Experts confess that herd immunity is not achievable unless the rate of confirmed antibodies within the population is at least 60%. Even though 70,000 participants took serology tests to determine whether they had developed antibodies from exposure to the coronavirus, only a meager population of 5% had developed antibodies.
However, the antibodies disappeared after a few weeks. The survey revealed that between the first and second rounds of testing, 7% of subjects no longer tested positive for antibodies. Between the first and final rounds, this velocity of the loss of antibodies rose to 14%, suggesting that temporary antibody immunity only lingers up to a range of several weeks to a few months.
Furthermore, it is uncertain whether the presence of antibodies protects people from reinfection.
“Not being able to detect antibodies does not mean that these people are not immunologically protected,” explained Marina Pollán, the director of Spain’s National Epidemiological Center.
The director of the Carlos III Institute, Raquel Yotti, said that 95% of the population is still vulnerable. “We cannot relax,” she said, explaining that we don’t know the exact extent to which antibodies protect from reinfection, if at all.
More studies need to be done about whether, and if so, how long and well, antibodies that act as natural vaccines can protect the body against the coronavirus.