The Covid-19 pandemic has caused a lot of confusion and fear among people all over the world. One of the most important questions that people have is how to protect themselves from the virus. One of the most effective ways to do this is to understand immunity and how it works. Immunity is the body's ability to fight off a disease or virus.
When herd immunity is achieved, it means that a large percentage of the population has become immune to a particular virus or disease, making it difficult for it to spread. This is why it is important to understand how immunity works and how it can be achieved. When a person becomes infected with Covid-19, the virus enters their body through the respiratory tract. This means that the immune response is centered around the respiratory system, where it leaves antibodies and memory cells in an ideal location to deal with the next infection.
In contrast, most vaccines enter the body through the bloodstream, away from the nose and lungs; the antibodies and memory cells that cause these vaccines take some time to reach the airways. The most recent studies suggest that hybrid immunity is due, at least in part, to immune agents called memory B cells. Most of the antibodies produced after infection or vaccination come from short-lived cells called plasmoblasts, and antibody levels drop when these cells inevitably die. Once plasmoblasts disappear, the primary source of antibodies becomes much rarer memory B cells that are triggered by infection or vaccination.
Developing immunity to a pathogen through natural infection is a multi-step process that usually takes place for 1 to 2 weeks. The body responds immediately to a viral infection with a nonspecific innate response in which macrophages, neutrophils and dendritic cells slow the progress of the virus and may even prevent it from causing symptoms. This nonspecific response is followed by an adaptive response in which the body produces antibodies that specifically bind to the virus. These antibodies are proteins called immunoglobulins.
The body also produces T cells that recognize and kill other cells infected with the virus. This combined adaptive response can eliminate the virus from the body and, if the response is strong enough, can prevent progression to serious illness or reinfection with the same virus. This process is often measured by the presence of antibodies in the blood. A study of SARS survivors showed that about 90% had functional virus-neutralizing antibodies and about 50% had strong T-cell responses.10 These observations reinforce confidence in a simple view that most survivors of severe COVID-19 would be expected to have antibodies protectors. One caveat is that most studies, whether of SARS survivors or patients with COVID-19, have focused on people who were hospitalized and had severe, symptomatic illness.
Similar data are urgently needed for people with SARS-CoV-2 infection who have not been hospitalized. It is important for everyone to understand how immunity works during this pandemic so they can protect themselves and their loved ones from getting sick. By understanding how immunity works, people can make informed decisions about their health and safety.