Europe is one of the hardest-hit continents across the globe, with Italy, Spain, and the United Kingdom reporting high numbers of infections and deaths caused by the coronavirus disease (COVID-19).
Meanwhile, some European countries have been successful in “flattening the curve” as they contained the spread of the virus. Switzerland has reported 31,131 confirmed cases and 1,939 deaths. The country is slowly easing restrictions and has opened its economy.
Now, a team of researchers at Geneva University Hospitals has found that less than 11 percent of the population in Geneva has contracted the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Their research is published in the journal The Lancet.
Antibody testing or serology testing can detect if a person has been infected with the coronavirus. It can help determine the extent of the outbreak and how much of the population has been exposed.
Antibodies, also known as immunoglobulins, are large Y-shaped proteins produced mainly by plasma cells. They are glycoproteins naturally produced by the body in response to foreign invaders (antigens), such as microorganisms.
The team used population-based serosurveys that measure SARS-CoV-2 antibodies to estimate infection rates and monitor the progression of the pandemic. The team estimated the weekly seroprevalence of the antibodies in Geneva, Switzerland.
“Population-based serosurveys measuring anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) antibodies provide one method for estimating infection rates and monitoring the progression of the epidemic,” the team wrote in the paper.
Called the SEROCoV-POP, the study covered former participants of the Bus Sante study and all their household members. They conducted a series of 12 consecutive weekly serosurveys among randomly selected participants from a previous survey, including their household members who are aged five years and older.
The team tested each participant for anti-SARS-CoV-2-IgG (immunoglobulin G) antibodies using a commercially available serologic test, the enzyme-linked immunosorbent assay (ELISA). Overall, the team carried the test among 2,766 people for over five weeks, between April 6 and May 9.
The results of the study, which was published in the journal The Lancet, show that at the time of the decline of the coronavirus pandemic in the country, only 10.8 percent of the population in Geneva had been infected with COVID-19. Further, compared to adults between 20 and 50 years old, children between 5 and 9 years old are three times less likely to be infected. Meanwhile, those over 65 years old had a significantly lower risk of being seropositive.
There is also a high concentration of infections within households. For instance, even if there is a low rate of seroprevalence among children, about 17.1 percent of children had at least one household member who tested positive.
In comparison, only 3 percent of participants who are more than 65 years old had a household member that tested positive for the novel coronavirus. This means that containment measures, especially among older adults, were effective. However, the team also emphasized that the elderly have a reduced ability to produce antibodies due to an aging immune system.
Effective lockdown measures
The findings suggest that only a minority of the population in Geneva had been exposed or infected during the pandemic wave, despite the high prevalence of infections in the country. This means that if being exposed would mean an immunity against the virus, the results highlight that the epidemic is far from over.
The team also noted that lockdown measures were effective in “flattening the curve” and preventing health care systems from being overwhelmed.
“This finding suggests that confinement measures were effective and that we cannot count on the reduction of susceptible individuals to play a major role in slowing transmission in the months to come,” the team concluded.
“As the world develops plans to find a new balance between minimizing the direct impacts of COVID-19 on those infected and the indirect effects on all of society, serological studies such as this are crucial for providing new insights about transmission and the otherwise hidden immunological state of the population,” they added.
Seroprevalence surveys are important tools to estimate the extent of the outbreak, helping prepare the appropriate public health response. The researchers will continue to test the population as the pandemic evolves.
The number of COVID-19 confirmed cases worldwide has topped 8 million people, with a death toll of at least 435,000.