In the US, the US Centers for Disease Control and Prevention estimates there have been an estimated 140 million Covid-19 infections, even though only 74.3 million cases have been reported as of January 31.
The data comes from the CDC's nationwide antibody seroprevalence survey, in which it is working with state, local, educational and commercial partners to test blood samples for antibodies to the coronavirus that result from infection, not vaccination. . By measuring Covid-19 seroprevalence, the study provides an estimate of the percentage of the population that was previously infected.
Blood samples are submitted to commercial laboratories for unrelated reasons, such as routine medical examinations, and identifying information is removed. Every two weeks, the researchers collected data from these samples, which include all 50 states, Washington, DC and Puerto Rico.
The agency estimates that by the end of January, about 43% of the country had the virus, including about 60% of children under the age of 18, nearly half of those aged 18 to 49, 37% of those 50 to 64, and 23% of them. Were. 65 and older.
Wisconsin has the highest seroprevalence, with an estimated 56.1% of the population infected with the coronavirus at some point. Vermont has the lowest at 17.8%. Estimates for Nevada, Utah, Arizona and North Dakota could not be provided due to the small number of samples from these states.
"I think it reflects more risk than immunity," said Dr., dean of the National School of Tropical Medicine at Baylor College of Medicine. Peter Hotez said. "I think what people should take away from this, almost half of the country is infected with Kovid-19, which is very extraordinary in itself."
The figures recorded from this seroprevalence survey are a huge jump from the total number of 74.3 million COVID-19 cases, which are measured using antigen testing or PCR testing of viral RNA. This difference may lie with a large proportion of asymptomatic or mild cases of COVID-19 that are not identified through testing, leading to an underestimation of total COVID-19 infections. Many people have recently also been relying on at-home COVID-19 antigen tests, which are not usually reflected in the CDC database.
Keri Althoff, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, told CNN that although CDC data can accurately tell who has antibodies or not, "what doesn't tell us: are those antibodies really." Is it enough to protect me from infection if the virus gets in that person's way again?"
The presence of antibodies does not necessarily mean protection against reinfection, and the survey does not measure how much antibody is present.
Studies have shown that the level of protective antibodies produced by infection can last longer than vaccination, but the CDC does not recommend using antibody testing to assess immunity to COVID-19.
"Covid infections themselves have created a lot of immunity. How long-lasting, how strong, the duration of that immunity, remains to be determined," said Dr. William Schaffner, a professor in the Department of Infectious Diseases at Vanderbilt University Medical Center. Center.
At the end of November, there were 102.9 million infections, according to CDC estimates. This would mean that there were more than 30 million infections in December and January as the Omicron wave spread through the country.
According to Hotez, the Omicron variant primarily affects the upper respiratory system, "and there is literature out there that says upper respiratory coronaviruses don't inspire much in terms of sustainable protection," he told CNN.
While it is not possible to draw conclusions about overall immunity against reinfection from these studies, they provide scientists and policy makers with a broad overview of how populations were affected by the pandemic.
"These data are designed to give us a sense of: What is the magnitude of the issue? It's like looking at some mountains in a big plain. You can see where the mountains rise, where they peak and where they fall. You don't have to count every tree to get the big picture," Schaffner said.
For example, due to declining hospitalizations and mortality, this data may explain why.
"These data ... give us some hope, assuming that this protection lasts for a while, that we can continue to plan about moving from the pandemic phase to the endemic phase," Schaffner said. "These data undoubtedly played an important role in the CDC's decision to revise its masking recommendations."
However, there are limits to the data. Althoff said that because this is the source of blood work done for non-Covid purposes, it is important to consider who is being omitted from the study.
"Who has done the blood work? People who have access to health care. And what do we know about this virus? ... she said, noting that the seroprevalence measure is probably underestimated.
Still, the data provide a snapshot of one source of immunity for the US population.
"As we're withdrawing these mandates ... it's important to know that we've got a good cushion of population immunity right now. And we have to watch it closely, because it will subside," Althoff said.