Story at a glance
- Sterilizing immunity could be achieved if neutralizing antibodies bind to a pathogen and prevent it from entering a cell to replicate in.
- Not all vaccines induce sterilizing immunity.
- Coronavirus vaccines show promise, but may not produce sterilizing immunity.
Experts are not certain what it means for a person’s health to have antibodies to SARS-CoV-2, the coronavirus that causes COVID-19. We don’t know if having antibodies means the person has immunity against the disease, and we don’t know if they do have immunity how long it may last.
Some of the concepts that researchers are thinking about include sterilizing immunity and neutralizing antibodies. Here’s some background about these ideas related to the coronavirus pandemic and current vaccine development efforts.
What is sterilizing immunity?
Sterilizing immunity means that the immune system is able to stop a pathogen, including viruses, from replicating within your body.
This typically happens when immune cells in the body are able to bind to the pathogen in places that prevent it from being able to enter a cell where it can start making copies of itself. Some of these immune cells may produce sterilizing antibodies, which are proteins that recognize specific proteins and structures on the surfaces of pathogens.
To achieve sterilizing immunity, your body needs to produce enough neutralizing antibodies and it needs to be able to do so in the long term. Ideally, it leads to life-long immunity.
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What it means for vaccine development
Not all vaccines produce an immune response that is sterilizing, and neither do they need to to be effective at preventing disease. “Many vaccines are primarily intended to prevent disease and do not necessarily protect against infection,” according to the World Health Organization (WHO). In this case, disease means the response of the body to a pathogen. It’s the illness and all the symptoms of the disease.
For example, the inactivated poliovirus vaccine does not produce sterilizing immunity and is 90 percent or more effective. A vaccine can lessen the ability of a pathogen to produce a disease response without sterilizing it. If it does sterilize against a pathogen, it can prevent infection. For example, the human papillomavirus vaccine induces sterilizing immunity.
For SARS-CoV-2, researchers are using a multitude of approaches to vaccine development, targeting various mechanisms to stop the coronavirus. For example, the Oxford vaccine candidate is reported to have produced neutralizing antibodies in monkeys, but it’s unknown how long they last. This vaccine is a “purified inactivated SARS-CoV-2 virus vaccine candidate.” The Moderna vaccine candidate also seems to have produced neutralizing antibodies and is an mRNA vaccine that is a genetic sequence that gets the immune cells to produce antibodies.
Part of the vaccine development process is testing how big of a dose of the vaccine is necessary to protect against the disease effectively. Although these vaccine candidates have induced the production of neutralizing antibodies, we don’t know yet what level of antibodies are necessary to prevent illness after exposure to the coronavirus.
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One expert told STAT they do not think sterilizing immunity can be achieved for COVID-19 because the immunity may not be long lasting. “I think we really need to focus on what are the fastest achievable true public health goals of the vaccine, which is protecting the vulnerable people against pneumonia and protecting health care workers as well,” says Vincent Munster at the National Institutes of Health.
What do antibody tests tell us?
Most antibody tests that are currently available are testing for IgG antibodies. The antibody test results aren’t very useful to the individuals because of prior mentioned uncertainties, but the information on the population level may be valuable to epidemiologists and researchers who are trying to estimate the outbreak numbers.
While some local experts and governments are encouraging people to get antibody tests, the test results should be used to make policy or to change behaviors around health and safety. It’s still important to follow public health protocols because we also don’t fully understand yet whether someone can get reinfected and spread the virus even if they have had COVID-19 already.
For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.
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