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How Effective Will Herd Immunity Be Against COVID-19?

May 06, 2020

In the fight against any virus, knowing a large number of people are immune to infection increases the sense of overall safety.

It’s a concept called “herd immunity,” when a large percentage of people in a population are immune to an infection and, therefore, unable to spread it to others. Immunity generally comes after exposure to the virus through the body’s response in creating protective antibodies that ward it off. It also comes through the use of a vaccine, which does not yet exist for COVID-19.

Infectious disease experts estimate that 50 percent to 66 percent of Americans will need to have such antibodies insulating them against COVID-19 before society can successfully reopen. But it’s still unclear how effective these antibodies are against possible reinfection.

“The virus mutates multiple times and we’re still learning about it,” said Dr. Ajay Kumar, chief clinical officer with Hartford HealthCare, in the system’s daily media briefing May 6. “This brings significant concern regarding how to prepare.”

Now that hospitalizations in Connecticut have peaked in the first wave of the COVID-19 pandemic, he said more work needs to be done to determine how many people were infected and might possess protective antibodies. This would help understand whether herd immunity exists here, helping to keep the virus from spreading even further.

“We need (to exercise) a significant amount of caution in this plateau phase,” he said.

He added that HHC is ramping up an contact-tracing system, with about 70 people trained to look into a 24- to 48-hour history of personal contact for people who test positive for COVID-19.

“It’s standard practice in hospitals for all outbreaks,” Dr. Kumar said.

The focus for current contact tracing efforts is early “identification, containment and mitigation.” This can lower the risk of disease spreading by alerting those who have been in contact with an infected person so they can quarantine themselves away from others.

The system’s tracking process kicks in, he explained, after a HHC staff member tests positive for COVID-19. Patients who test positive are already isolated to contain the spread.

This work will continue as the level of infection declines through the summer, Dr. Kumar noted.

“This is a gradual, not a precipitous decline,” he said. “The next phase will be the recovery phase.”

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