“The vast majority of people in most countries are at risk of contracting this virus. Seroprevalence (the level of a pathogen in a population, as measured in blood serum) surveys suggest that in most countries, less than 10% of the population has been infected,” Ghebreyesus detailed.
Additionally, he explained that the world does not know enough about the immunity that people who have contracted Covid-19, pointing out that some individuals have been infected once again.
“Most people infected with the virus develop an immune response in the first few weeks, but we do not know if that response is strong or long-lasting, or if it differs from person to person,” he explained.
He pointed out that the concept of herd immunity is used in vaccination campaigns and recalled that for smallpox, 95% of the population must be vaccinated for the remaining 5% to be protected. For polio, this rate is 80%.