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Coronavirus Variant Strains Could Impact Herd Immunity

According to the CDC, with immunization and continued mitigations strategies, herd immunity to COVID-19 could be achieved with a 70 to 75 percent immunization rate. That rate rises if variant strains become dominant.

by Jim McKay / February 5, 2021

Although the United States has begun to climb down from the latest COVID-19 surge and vaccinations are being administered, the CDC, in a call this week, cautioned against complacency, especially with the emergency of variant strains of the virus.  

The holiday surge has passed, but Super Bowl Sunday presents another hurdle in the fight against the coronavirus, even as vaccinations are ramping up. The CDC urges people to continue with the mitigation effort — mask wearing, social distancing and staying away from crowds — especially in the face of the variant strains.  

CDC doctors on the call also stressed that citizens should trust the vaccines and follow through on getting both doses. The vaccines work, and though there have been cases of side effects, those are relatively mild and few, especially when compared to the alternative of being infected with the virus. 

Dr. Jay Butler, deputy director for infectious diseases for the CDC, said that during the 45 minutes to an hour it will have taken to complete the call, an estimated 16,400 of every 1 million people diagnosed with COVID-19 will die based on recent death rates. He compared that eventuality with the side effects associated with getting vaccinated.  

“It’s important to note the mild side effects of the vaccine, like pain where you got the shot or feeling tired after getting immunized,” Butler said. “The reliable data tell us that more than half of people have reported tiredness and some pain, but most are able to continue with daily activities.”  

He said the vaccines work and data show that just around 71 cases of anaphylaxis (an allergic reaction) have occurred in the first 18 million doses administered.  

The vaccines are important to achieve herd immunity, as are the mitigation measures previously mentioned and that is what it will take to effectively stop the virus. Dr. John Brooks, chief medical officer for the CDC’s COVID-19 response, said herd immunity could be achieved when about 70 to 75 percent of the population gets immunized. That number could be raised to 80 to 85 percent if the variants become dominant before herd immunity is reached.  

The CDC also is seeking to clarify that it’s important to get both doses of whatever vaccine people are getting, even if they have to mix the kind of vaccine and even if the timeline is not optimum. 

“Getting the second dose is incredibly important to keep you protected,” Butler said. “Data from clinical trials do show some degree of protection after a single dose, but the highest levels of efficacy are [getting a second dose] a week or longer after the first dose.” 

He said in some rare cases people may not be able to get a dose of the same vaccination — some people are forgetting which vaccine they’re getting or losing documentation — and should seek to get a dose of whatever is available as close to the recommended interval. “In this instance, the second dose may be given up to two weeks or 42 days after the first,” Butler said. “We’re not advocating that people delay, but data from the trials supports this range.” 

The CDC is continuing to surveil the virus and gather data on a daily basis to provide to the public, participants on the call said. State public health labs are collectively providing about 1,500 specimens every two weeks to CDC for study. The CDC also said it’s contracting with several large commercial labs and testing tens of thousands of coronarius-positive specimens each month. 

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