Herd Immunity Unveiled: Unveiling the Number of Americans Possessing COVID-19 Antibodies

**Antibodies and Immunity: A Look at COVID-19 Serosurveys**


Antibodies to SARS-CoV-2, the virus responsible for COVID-19, were found in the blood of 96.4% of Americans over the age of 16 by September 2022. This data was obtained from a serosurvey conducted on blood samples from donors.

**Understanding Serosurveys and Immunity**

Serosurveys help researchers estimate the number of people exposed to the coronavirus, either through vaccination or infection. By analyzing the antibodies in the blood, researchers can determine different types of immunity: infection-derived, vaccine-derived, and hybrid.

**Breaking Down Antibodies and Immunity**

COVID-19 vaccines in the United States are based on the spike protein of the virus. If a person’s blood only contains anti-S antibodies targeting the spike protein, it means they have been vaccinated but not infected. On the other hand, the presence of anti-N antibodies indicates a past infection with SARS-CoV-2. To identify someone with hybrid immunity, researchers need to match individuals with anti-N antibodies to an official vaccination database.

**Exploring the 3.6% without Antibodies**

It is known that antibody levels decrease in the months following a COVID-19 infection or vaccination. Additionally, not every infection leads to detectable antibodies, especially in mild or asymptomatic cases. Furthermore, the accuracy of antibody tests is not perfect, leading to some false negatives. All these factors suggest that the 96.4% figure is likely an underestimate.

**A Clearer Picture of Virus Spread: The Role of Serosurveys**

Serosurveys provide valuable insights into the infection rates among different populations. Unlike relying on positive PCR tests or self-reporting, serosurveys are less biased by factors such as access to care and the severity of symptoms. Research conducted in Chennai, India, and Salvador, Brazil, found similar or even higher seroprevalence in children compared to young adults, challenging the notion that children are less susceptible to the virus.

**Implications for Future Waves: Understanding Immunity**

Antibodies not only serve as markers of past infection but also play a role in preventing future infections. Serosurveys can help determine the levels of immunity within a population. While immunity to diseases like measles is lifelong, SARS-CoV-2 has continually evolved new variants that can reinfect individuals despite their antibodies. However, studies have shown that individuals with hybrid immunity are more protected against future infections and variants. This information can be useful for targeting specific groups with vaccination campaigns.


In conclusion, serosurveys provide valuable information about COVID-19 immunity and infection rates. The presence of antibodies in the blood indicates previous exposure to the virus, whether through vaccination or infection. Understanding the different types of immunity can help in assessing levels of protection against future waves and variants. Serosurveys offer a less biased perspective on the spread of the virus compared to other testing methods. Further research and analysis of serosurvey data will contribute to the ongoing fight against COVID-19.

*This article is republished from The Conversation under a Creative Commons license. Read the original article.*

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