With recent studies in the U.S., Spain, Switzerland, Sweden and China all revealing a low rate of nationwide seroprevalence, scientists are speaking out against the herd immunity technique touted by some politicians.
“In light of these findings, any proposed approach to achieve herd immunity through natural infection is not only highly unethical, but also unachievable,” Swiss researchers Isabelle Eckerle and Benjamin Meyer write in a commentary published this week in The Lancet.
The commentary comes the same day as the publication of a seroepidemiological study conducted in Spain that found 95% of the population does not have antibodies that would protect them from COVID-19. In other words, only 5% of the population may be immune to COVID-19, including those who have already contracted the virus. The study, which included more than 61,000 participants, also found that 14% of people who tested positive for COVID-19 antibodies in the first round of testing no longer tested positive in follow-up tests conducted weeks later. This hints at the idea that—as has been suggested by other studies—immunity to COVID-19 is especially short-lived in people who experience mild or no symptoms. The research team used two IgG antibody tests aimed at different SARS-CoV-2 antigens to test a random, representative sample of Spaniards in what is believed to be the largest seroprevalence study in Europe.
The results are particularly concerning as Spain was one of the hardest-hit COVID-19 countries, with over 28,000 recorded deaths. That being said, the researchers did find higher levels of antibody prevalence in Spain’s most densely populated cities—including a 10% rate in Madrid and a 7% rate in Barcelona. However, they also found that at least a third of individuals who were asymptomatic did indeed have antibodies against SARS-CoV-2—a fact that supports public health initiatives such as mask-wearing and social distancing even if a person has no virus symptoms.
A smaller Swiss study of 2,766 participants conducted throughout April and May revealed that almost 11% of those living in Geneva had developed antibodies to COVID-19. Since herd immunity is generally established around 60%, that number is still very low—even if it is double what was detected in Spain.
“At what appears to be the tail end of the first wave of the pandemic in Switzerland, about 1 in 10 people have developed detectable antibodies against SARS-CoV-2, despite the fact that it was one of the more heavily affected areas in Europe,” the authors write in the paper. “Thus, assuming that the presence of the IgG antibodies measured in this study is, at least in the short term, associated with protection, these results highlight that the vast majority of the population is still immunologically naive to this new virus.”
In a Swedish study of 1,000 participants, 7% of Stockholm residents developed COVID-19 antibodies by the end of April. Additionally, a study conducted in Wuhan, China about 4 to 8 weeks after the peak of infection reported an incredibly low seroprevalence between 3 and 4%—even in high-risk health care workers and other hospital employees.
“The key finding from these representative cohorts is that most of the population appears to have remained unexposed to SARS-CoV-2, even in areas with widespread virus circulation. These findings are further supported by the observation that even countries without strict lockdown measures have reported similarly low seroprevalence…leaving them far from reaching natural herd immunity in the population,” said Eckerle and Meyer.
Photo: A May 2020 photo of cafes in Malaga, Spain reopening for business.