COVID-19 antibodies can vanish in weeks, study says. What’s it mean for herd immunity?

A large study from Spain showed that antibodies can disappear weeks after people have tested positive, causing some to question how possible it will be to attain herd immunity.

A study published in medical journal Lancet showed 14% of people who tested positive for antibodies no longer had antibodies weeks later.

“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,” the report reads.

Herd immunity is when enough of a population becomes immune to a disease through vaccine or already getting sick to make the spread unlikely between people in the community, according to the Centers for Disease Control and Prevention. Herd immunity also protects newborns and people who can’t be vaccinated because it helps decrease person-to-person spread, the CDC said.

The study was conducted from April 27 to May 11 and involved 61,075 participants in Spain who answered a questionnaire on COVID-19 symptoms, received an antibody test, and donated a blood sample for more testing if they agreed.

The study’s author, Marina Pollán, director of the National Center for Epidemiology, told CNN that some experts think herd immunity could be reached when about 60% of the population have antibodies. “But we are very far from achieving that number.”

“Immunity can be incomplete, it can be transitory, it can last for just a short time and then disappear,” Raquel Yotti, the director of Spain’s Carlos III Health Institute, which contributed to the study, told Business Insider.

Herd immunity worked for Norway during the swine flu epidemic through natural immunity and vaccination, according to Heathline.

However, herd immunity doesn’t work against every illness and isn’t a good enough alternative to getting vaccinated, Healthline reported.

“They’re making a big assumption ... young people can get the disease and won’t die,” Natalie Dean of the University of Florida who specializes in infectious disease epidemiology, told Business Insider. “We don’t have enough data to support that. We’re seeing 30-year-olds in the ICU and we don’t know if those people aren’t going to have long-term breathing problems and lung problems.”

Spain has been hit hard by the pandemic, with more than 252,000 people testing positive for COVID-19 and more than 28,000 people dying from the virus as of July 8, according to Johns Hopkins University.