A patient having blood drawn for a Covid-19 antibody test
Even in areas hard-hit by Covid-19, few people test positive for antibodies, meaning that hopes for herd immunity against the disease may be futile without a vaccine, according to a new Spanish study.
Conducted by researchers at the Carlos III Health Institute in Madrid and published in The Lancet Monday, the study included 61,075 people in 35,883 randomly selected households throughout the country. After completing a questionnaire between April 27 and May 11 on Covid-19 symptoms, participants received a point-of-care antibody test, followed by a blood draw for a laboratory immunoassay test if they agreed to it. Overall, the study found that only 5% of participants showed a positive result on the point-of-care test, while 4.6% showed a positive result on the lab test. Results varied considerably by region, with residents of Madrid showing a prevalence greater than 10%, while residents of coastal areas showed a prevalence of less than 3%.
Among 195 participants who had received a positive RT-PCR test for Covid-19 more than two weeks prior, positive tests for antibodies ranged from around 88-92%. In 7,273 individuals who had lost their sense of smell or showed at least three symptoms, 15.3-19.3% tested positive for antibodies, while 21.9-35.8% of those who were asymptomatic did as well, meaning that about one-third of infected people did not show symptoms.
“The relatively low seroprevalence observed in the context of an intense epidemic in Spain might serve as a reference to other countries,” the researchers wrote. “At present, herd immunity is difficult to achieve without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems.”
With 250,545 confirmed cases and 28,385 deaths as of Monday, Spain has the third-highest prevalence of Covid-19 cases in Europe, after Russia and the U.K. The U.S. leads by far, with 2.9 million of the world’s 11.5 million cases and 130,007 of its 535,185 deaths. Spain issued new lockdown orders in its Galicia and Catalonia regions amid renewed outbreaks of Covid-19 in those areas, though Europe in general has managed to get the outbreak largely under control. By contrast, the U.S. has seen record spikes in states that reopened prematurely, and it is among those countries whose failure to control the outbreak has resulted in its citizens being mostly barred from traveling to the European Union.
Absent a vaccine being proven safe and effective – which may not become available until next year – there was some hope early on among some experts that herd immunity could provide protection against the disease. However, it remains unclear how protective antibodies against SARS-CoV-2 are or for how long. Moreover, countries that attempted to use herd immunity, such as the U.K. and Sweden, have been among those experiencing the most difficulty getting the outbreak under control.
A Deep-dive Into Specialty Pharma
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