GENEVA, Switzerland — The chief of the World Health Organization (WHO) said on Monday that herd immunity against COVID-19 is “scientifically and ethically problematic.”
Speaking at a press briefing, WHO Director-General Tedros Adhanom Ghebreyesus said that herd immunity is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached.
“For example, herd immunity against measles requires about 95 percent of a population to be vaccinated. The remaining five percent will be protected by the fact that measles will not spread among those who are vaccinated. For polio, the threshold is about 80 percent,” he said.
“Herd immunity is achieved by protecting people from a virus, not by exposing them to it,” he said, adding that “it has never been used as a strategy for responding to an outbreak.”
As for the ongoing COVID-19 pandemic, he noted that the world still doesn’t know enough about immunity to COVID-19, including how strong or lasting that immune response is, or how it differs for different people, let alone some examples of people being infected for a second time.
“We have some clues, but we don’t have the complete picture,” he said.
Additionally, the vast majority of people in most countries remain susceptible to this virus, meaning, letting the virus circulate unchecked could lead to unnecessary infections, suffering, and death.
He said the world is only beginning to understand the long-term health impacts among people with COVID-19 and it’s simply “unethical” to allow a dangerous virus that is not fully understood to run free.
Instead of herd immunity, the WHO chief urged countries to stick to measures already implemented and proven effective to control transmission and save lives, such as preventing amplifying events, protect the vulnerable, as well as empowering, educating, and engaging communities, in addition to finding, isolating, testing, and caring for cases, and tracing and quarantining their contacts.
“There are no shortcuts and no silver bullets. The answer is a comprehensive approach, using every tool in the toolbox,” Ghebreyesus said.
As the world is struggling to control the pandemic, countries across the globe – among them European Union nations, China, Russia, the United Kingdom and the United States – are racing to find a vaccine.
According to the website of the WHO, as of Oct. 2, there were 193 COVID-19 candidate vaccines being developed worldwide, and 42 of them were in clinical trials.
COVID-19 patients may experience more severe symptoms the second time they are infected, according to research released Tuesday confirming it is possible to catch the potentially deadly disease more than once.
A study published in The Lancet Infectious Diseases journal charts the first confirmed case of COVID-19 reinfection in the United States – the country worst hit by the pandemic – and indicates that exposure to the virus may not guarantee future immunity.
The patient, a 25-year-old Nevada man, was infected with two distinct variants of SARS-CoV-2, the virus that causes Covid-19, within a 48-day time frame. The second infection was more severe than the first, resulting in the patient being hospitalized with oxygen support.
The paper noted four other cases of reinfection confirmed globally, with one patient each in Belgium, the Netherlands, Hong Kong, and Ecuador.
Experts said the prospect of reinfection could have a profound impact on how the world battles through the pandemic. In particular, it could influence the hunt for a vaccine – the currently Holy Grail of pharmaceutical research.
“The possibility of reinfections could have significant implications for our understanding of COVID-19 immunity, especially in the absence of an effective vaccine,’’ said Mark Pandori, for the Nevada State Public Health Laboratory and lead study author.
“We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some of these second infections, while rare, are presenting as more severe.”
Vaccines work by triggering the body’s natural immune response to a certain pathogen, arming it with antibodies it to fight off future waves of infection. But it is not at all clear how long COVID-19 antibodies last.
For some diseases, such as measles, infection confers lifelong immunity. For other pathogens, immunity may be fleeting at best.
The authors said the US patient could have been exposed to a very high dose of the virus the second time around, triggering a more acute reaction.
Alternatively, it may have been a more virulent strain of the virus.
Another hypothesis is a mechanism known as antibody dependent enhancement – that is, when antibodies actually make subsequent infections worse, such as with dengue fever.