By the fall of 2022, 96.4% of Americans had COVID-19 antibodies in their blood

(conversation) – Antibodies to SARS-CoV-2, the virus that causes the novel coronavirus disease (COVID-19), were present in the blood. 96.4% of Americans are 16 and older By September 2022. Serum survey – Analytical tests for the presence of these immune defense molecules – are performed on samples from blood donors.

Such serosurveys help researchers estimate how many people have been exposed to some part of the coronavirus, such as through vaccinations or infections. Both can cause her to develop antibodies to SARS-CoV-2. And by identifying what types of antibodies are in someone’s blood, researchers can classify 96.4% into different types of immunity, such as infection-derived, vaccine-derived, or hybrid.

The novel coronavirus vaccine used in the United States is based only on part of the virus – Spike, or S, protein. Researchers can tell that a person has been vaccinated and not infected if their blood contains only anti-S antibodies that target the spike protein. If someone has anti-N antibodies that target the viral nucleocapsid protein, it’s a sign of SARS-CoV-2 infection. To reliably identify people with hybrid immunity, researchers must match people with anti-N antibodies to official vaccination databases.

What about the 3.6% who have no antibodies?

immunologists know that Antibody levels decrease after a few months COVID-19 or vaccination, which is Suitable for many pathogens. Some people may have had antibodies at one point, but they are undetectable now. And not all infections cause a detectable antibody response, especially if the infection is mild or asymptomatic.

Another factor is Antibody test accuracy. No test is perfect, so a small number of people who do have antibodies may test negative.

Taken together, these considerations make the 96.4% figure likely an underestimate. It is reasonable to conclude that there are very few people in this population who have never had SARS-CoV-2 and who have not been vaccinated against the novel coronavirus (COVID-19).

Get a clearer picture of the spread of the virus

Serologic studies help us understand how different types of people, such as different ages and races, may have been infected. For this purpose, serosurveys are much more reliable than using data from people who test positive by PCR or report a positive rapid antigen test. This is because whether a person tests positive or not is highly influenced by access to care and medical practice. and the severity of your illness. These are the so-called sources of bias.

This bias has two effects. One can lead to a significant underestimation of the proportion of infected people in the population as a whole, and the other can lead to erroneous differences between groups. For example, people with mild symptoms are less likely to be tested and are more likely to be young. Researchers may erroneously conclude that these people are not actually infected with the virus because they have not been tested.

Viewing antibodies as markers of infection is not biased by such behavioral factors. Many serosurveys. We worked in Chennai, Indiaand Salvador, Brazilfound similar or higher seroprevalence in children compared with adolescents, contradicting earlier theories that children are less susceptible to the virus. Rather, our results suggested that infection in children was less likely to be detected.

What does this stat mean for future waves?

Antibodies are not just markers of past infections. Part of their job is to prevent future infections with the same pathogen. Therefore, serosurveys can be used to understand population immunity levels.

For some diseases, such as measles, immunity is essentially lifelong, and having antibodies means protection. But that is not the case with SARS-CoV-2. This is because the virus has continuously evolved new variants that can reinfect people even if they have antibodies.

Still not many studies show people with hybrid immunity will be more protected It is more effective against future infections and variants than having only vaccine or infection-derived immunity. To target specific groups in vaccination campaigns, it may be useful to know the proportion of the population with single-source immunity.