Aiming to achieve herd immunity naturally is ‘dangerous’, WH
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Dr. Mike Ryan, the executive director of the World Health Organization (WHO) health emergency program, said the concept of herd immunity is “dangerous.”

“This idea that maybe countries that had lax measures and haven’t done anything will all of a sudden magically reach some herd immunity – and so what if we lose a few old people along the way? This is a really dangerous, dangerous calculation," Ryan said at a news briefing.

• The term herd immunity is taken from_veterinary epidemiology, here people are “concerned with the overall health of the herd, and individual animals in that sense, doesn’t matter,” Ryan said. “Humans are not herds.”

• Challenges
While antibodies (IgG and IgM) against coronavirus generally develop in one–three weeks after infection, some people do not seem to develop a humoral immune response, as reflected by detectable antibodies. It is unclear why this happens.

• Durability of response
Also, how long neutralizing antibodies against the virus would last is currently not known, though one study found that they persist for up to 40 days from_symptom onset. In the case of the 2002 SARS, levels of IgG remained high for nearly four-five months before declining during the next two-three years. For MERS, the antibodies persisted for up to 34 months.

• Reinfections possible
Reinfection is mightily possible with at least three of the four coronaviruses which cause the common cold. "Evidence suggests that possibilities include both short-lived protective immunity and re-exposure to genetically distinct forms of the same viral strain,” they write.

• Cautions
But WHO cautions that “there is currently no evidence that people who have recovered COVID-19 and have antibodies are protected from_a second infection”.

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