What is herd immunity and could it work with COVID-19?
Herd immunity is when a virus can no longer spread easily because enough people are immune to it. That
lowers the chances of the virus jumping from person to person and reaching those who haven’t been
infected yet.
People can become immune to certain viruses after surviving infection or being vaccinated. Typically, at
least 70% of a population must be immune to achieve herd immunity. But how long immunity lasts varies
depending on the virus, and it’s not yet known how long COVID-19 survivors might have that protection.

How easily the virus spreads also plays a key role.
Say, for example, someone who’s infected with a particular virus typically transmits it to two others.
The chances of that person passing it on to others would be lower if half the population is already
immune, said Dr. Walter Orenstein, a vaccine expert at Emory University.
The odds of transmission fall further if even more of the population is immune. That could cause new
infections to die out.
But if a virus is more infectious, a higher percentage of people would need to have immunity to stop the
spread and achieve herd immunity, Orenstein said.
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Read previous Viral Questions:
— Will employee temperature checks make workplaces safe?
— How should I clean and store my face mask?