What if more of us have fought COVID-19 than we think?

So-called serological research looks for antibodies in the blood that fight the disease and how many of us have them. Other research looks at how long these antibodies last. The latest results from these studies are said to show us two kinds of bad news: that immunity after exposure to the disease is not as safe, and that the number of us who have been exposed to and fight COVID-19 is fewer. than expected

This pushes our collective immunity goal further into the distance, potentially even questioning it entirely. But when measuring antibodies to COVID-19, could we have missed other blood markers that help fight the disease? Is it possible that we are underestimating both the duration of immunity and the proximity of herd immunity?

Consider some recent observations.

COVID-19 cases may be emerging across the state and nation, but at long-standing virus hotspots like Wuhan, China; New York; Spain; Sweden and the Lombardy region in Italy, the number of cases and deaths have steadily decreased. Lombardy, once the source of a horrible COVID-19 outbreak, recently had two consecutive days with no virus-related deaths.

These declines have come despite seroprevalence surveys that only 5, 15, or 20% of the population have had the disease in those locations, and other data suggesting that the antibodies fade rapidly. For health officials, such large declines, with only a small exposure to disease in the population, demonstrate the power of confinements, social distancing, masking, handwashing, and PPE.

Others have begun to discuss something much more hopeful. While masking, social distancing, and handwashing and blockades are powerful tools to reduce the spread of the disease, they are not enough to earn credit for so many critical points that have cooled down. Instead, they say, more of us can be immune than we think.

“When we are exposed to an infection, two major types of immune responses occur,” says Dr. Vincent Rajkumar, an oncologist at the Mayo Clinic who conducts research on the type of blood cells that help us fight infection. “One is called antibody-mediated immunity. This is where specific proteins called antibodies are produced to fight infection.”

“The second type of response is called cell-mediated (or T-cell) immunity. No antibodies are produced here, but you actually have specific cells that attack the causative infection.” Serological studies measure antibodies, but they do not measure cellular immunity.

In addition, Rajkkumar says, serological tests may omit antibodies that are present in a lower concentration than the assay can detect, or we may have other antibodies directed at the virus than a given serological test is designed to identify.

“The virus has a lot of protein,” he says, “and it is possible that a person is developing antibodies against other parts of the virus that we are not checking.”

Some even wonder if recent vaccines in children make them less susceptible to poor COVID-19 results.

“In March, when we were all thinking aloud,” says Rajkumar, “one of the thoughts I had was: why were the children relatively protected from being seriously ill with COVID-19? Was it because of the multiple childhood vaccines that receive? a more sensitive immune system?

Answering these questions in the laboratory is not an easy task.

“We would have to do T-cell assays on a well-defined population to find out how many people have only antibodies, how many have only T-cell responses, and how many have both,” he explains. “So we need adequate monitoring to determine what proportion COVID-19 will receive in the future. Those studies are difficult to do.”

The researchers know that some people appear to have T cells that cross-react to SARS-Cov-2 from blood samples collected before the pandemic. A recent study from Sweden has shown that there are close family contacts who have reactive T cells after being exposed to COVID-19 without developing antibodies.

“I think that the great decrease in the new cases that we see in many critical points is explained in part by the masks, in part by the social distancing, and in part can be explained by a large part of the population that is already exposed.”

“All these observations together make us wonder if a larger proportion of the population is not susceptible to COVID-19 than current sero-prevalence studies suggest,” says Rajkumar.

Rajkumar has been sharing these questions on Twitter, and they are the subject of lively interactions between some of the best scientists in the country.

So if serology studies only show us part of the picture, how many of us are potentially immune to COVID-19?

“I think it is much higher,” says Rajkumar. “I think it is at least twice what sero prevalence studies report.”