About 83 percent of the U.S. population aged 16 and older has some degree of immunity to the coronavirus through vaccination or previous infection, a new study from the Centers for Disease Control and Prevention (CDC) estimates.
Based on antibody levels in blood samples from about 1.4 million patients, the CDC researchers estimate that 20 percent of Americans have immunity to previous infection — although the number varies by age and other demographics.
Experts previously cited 70 to 80 percent protection as a target for herd immunity, but now many are saying we need more vaccinations and boosters to protect against the super-contagious Indian ‘Delta’ strain.
Still, the study indicates the US has had many more Covid cases than have been officially reported — possibly more than double the official number.
More than 80 percent of Americans over the age of 16 have some degree of protection from Covid, a new study estimates. Pictured: Vaccination at a Central Falls, Rhode Island high school, February 2021
As of May 2021, 20 percent of Americans over the age of 16 have protection against a previous infection, while another 60 percent are protected by vaccination, the researchers estimate.
As of Sept. 2, 175 million Americans are now fully vaccinated — meaning they are protected from serious illness from Covid.
But millions of others are also protected to some degree, as they have recovered from a previous Covid case.
In fighting the coronavirus, a body’s immune system will remember how to respond to this invader – and will be better prepared for future Covid encounters.
The CDC counts about 39.5 million Americans who have become ill with Covid — or 39.5 million people with possible levels of immunity.
However, the actual number is likely much higher, as many people with mild cases or no cases were unaware that they needed to get Covid tested and thus were not recorded as cases.
A new CDC study – published in JAMA . on Thursday — suggests that this actual number accounts for about 20 percent of Americans over the age of 16.
The researchers determined this estimate with a seroprevalence survey — an estimate of the number of people with antibodies in their blood that indicate a past immune response to Covid.
For the study, the CDC used blood donation samples from all 50 states, Washington DC and Puerto Rico.
In total, about 1.4 million blood samples were examined. These samples were collected between July 2020 and May 2021.
The researchers included larger numbers of samples from blood donor regions with larger racial/ethnic minority populations, and made other analytical adjustments, in an effort to align their final estimates with the demographic composition of the U.S.
However, they acknowledged that a perfect match was not possible — and that other differences between the blood donors included in the study and the overall population were unlikely to be unexplained.
The final estimate: In May 2021, about 20 percent of Americans over the age of 16 had a previous Covid infection.
That number is up significantly from July 2020 (3.5 percent) and December 2020 (11.5 percent), indicating that millions of Americans were infected — and gained immunity — during the winter wave.
Combining these estimates with vaccination figures, the CDC researchers estimate that 83.3 percent of Americans over the age of 16 had some degree of protection against Covid by May 2021.
By May 2021, the Midwest and South had higher Covid protection against previous infection (left map), while all parts of the country had significant protection from vaccination (right map)
Protection varies by demographic group. In May 2021, the Midwest and South had higher rates of Covid antibodies from previous infection, compared to other regions — 23.5 percent and 22.2 percent, respectively.
The Midwest and South likely had higher previous infection rates in May as these regions were hit harder during the summer and winter peaks.
However, the Northeast had the highest overall immunity (prior infection plus vaccination), a total of 87.2 percent. The south had the lowest – 80.2 percent.
In a similar pattern, teens and young adults (aged 16 to 29) had the highest rates of Covid antibodies from infection – 27 percent in May 2021.
But this group had the lowest overall immunity, a rate of 76.1 percent. Teens and young adults are more likely to have mild Covid cases than their elderly, but they are also less likely to get vaccinated.
Seniors (over age 65) had the highest combined immunity rate, at 92 percent. According to CDC data, 82 percent of American seniors are fully vaccinated.
In some cases, the groups with the highest protection against previous Covid cases were also the groups with lower vaccination rates – leading to lower overall protection
Black and Hispanic/Latino Americans had higher rates of Covid antibodies from infection than other racial and ethnic groups – 30 percent and 21.1 percent, respectively.
Combined immunity rates (prior infection plus vaccination) were highest among Asian and white Americans — 91 percent and 83.8 percent, respectively.
This combined immunity rate was 79.2 percent for Black Americans and 81.5 percent for Hispanic/Latino Americans, reflecting the lower vaccination coverage in these groups.
The CDC’s blood draw study will run until at least December 2021, and the researchers say they plan to continue publishing data.
With more than 80 percent of Americans potentially protected from Covid, it’s easy to conclude that the country has achieved herd immunity.
After all, President Biden has made a 70 percent vaccination rate his national goal.
However, the Delta variant has changed the game. Now researchers say 95 percent or more Americans need to be protected to stop outbreaks.
The CDC researchers note that “additional research is needed” on the links between a previous infection and herd immunity.
“Infection-induced protection may decline faster than vaccine-induced protection,” they write.
For this reason, experts recommend that Americans be vaccinated, even if they have had a previous Covid infection.
Still, the study indicates that we have had many more Covid cases in the US than have been officially reported.
The CDC researchers estimate that, by July 2020, for every Covid case reported, two more could later be detected by blood tests.
By May 2021, that number dropped to one additional case for every case officially reported.
However, the number can now be higher again, just as much vaccinated people don’t seek tests for mild colds and other symptoms that may indicate a Covid breakthrough.