Over 60,000 people have been studied by Spanish researchers (Representation)
New Delhi:
A Spanish study published in The Lancet has questioned the feasibility of collective immunity – when enough people are infected with a virus to stop its spread – as a way to fight the COVID-19 pandemic.
For collective immunity to work, at least 70% of the population must be immunized to protect uninfected people, experts say.
The study of more than 60,000 people estimates that only around 5% of the Spanish population has developed antibodies, according to researchers, including those from the National Center for Epidemiology in Spain.
The objective of the population-based study was to estimate the seroprevalence – the level of a pathogen in a population, as measured in blood serum – of SARS-CoV-2 infection in Spain at the level national and regional.
About 35,883 households were selected from municipal lists using two-stage random sampling stratified by province and size of municipality, the researchers said.
From April 27 to May 11, 61,075 participants responded to a questionnaire on the history of symptoms compatible with COVID-19 and risk factors, among others.
“The prevalence of IgG antibodies was adjusted using sampling weights and post-stratification to account for differences in non-response rates by age group, sex and census tract income” , wrote the researchers in the medical journal.
“Using the results of the two tests, we calculated a range of seroprevalence maximizing either the specificity (positive for both tests) or the sensitivity (positive for either test),” they said.
The researchers noted that the seroprevalence was 5% by the point of care test and 4.6% by immunoassay, with no difference by sex and a lower seroprevalence in children under 10 years of age.
There was substantial geographic variability, with a higher prevalence around Madrid (more than 10%) and lower in the coastal areas (less than 3%), they said.
The results suggest that the majority of the Spanish population is HIV negative for SARS-CoV-2 infection, even in hotspot areas, according to the researchers.
“Most of the cases confirmed by PCR have detectable antibodies, but a significant proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of the infections determined by serology were asymptomatic”, wrote the researchers in the journal.
“These results underscore the need to maintain public health measures to avoid a new epidemic wave,” they said.
(With the exception of the title, this story was not edited by GalacticGaming staff and is published from a syndicated feed.)
