Severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, is the virus that causes coronavirus disease 19 (COVID-19). To prevent COVID-19, a person requires immunity to the virus. To attain immunity and protection, a person likely needs to either naturally recover from the disease or receive a COVID-19 vaccination.
Vaccination programs are rolling out worldwide to deploy safe and effective vaccines against COVID-19. At present, evidence suggests that roughly one-third of the world’s population have received at least one dose of a COVID-19 vaccine and approximately one-quarter are fully vaccinated.
A person can also develop immunity from COVID-19 following direct exposure to the virus, but this runs the risk of complications from the disease. While there is limited data on the length of immunity, evidence suggests it is a short term effective way to prevent infection. If enough people within a population become immune to a disease, they may achieve herd immunity, which can help protect people who may be unable to receive the vaccine.
In this article, we discuss immunity to SARS-CoV-2, including how to acquire it, how long it lasts, and whether it prevents infection.
A person has an innate immune system that acts as the first line of defense against pathogens. This refers to barriers, such as the skin and mucous membranes, that prevent harmful substances from entering the body.
Also known as
A person can acquire adaptive immunity through natural exposure to the pathogen, known as natural immunity, or introduction to an inactive portion of the pathogen through a vaccine, reffered to as vaccine-induced immunity. Either way, a person can produce a suitable immune response that is long lasting and sometimes lifelong.
Passive immunity is when a person receives antibodies to a disease rather than producing them through their immune system. For example, a newborn infant can receive passive immunity through the placenta, or a person can receive passive immunity through antibody-containing blood products.
This can be useful as passive immunity provides immediate protection, while adaptive may require weeks to develop. However, while adaptive immunity is long lasting, passive immunity typically only lasts for a few weeks or months.
Herd immunity, or
The percentage of the global population that needs to be immune to achieve herd immunity — called a threshold — varies by disease. Generally, thresholds are only achievable with high vaccination rates. While the herd immunity threshold is not known for COVID-19, evidence suggests it may require roughly 70% of the population to be immune to the disease.
While vaccination rates are increasing, some
People previously infected with COVID-19 develop natural immunity against the disease. Their immune system can recognize SARS-CoV-2 and immediately produce antibodies to fight off an infection. After identifying a pathogen, the immune system keeps special white blood cells — called memory cells — that go into action quickly to
Evidence from the World Health Organization (WHO) indicates that 90–99% of people with a SARS-CoV-2 infection develop protection against the virus. Individuals typically develop antibodies roughly
Currently, scientists measure immunity based on the presence of neutralizing antibodies (Nab) in the blood. These antibodies can neutralize the virus by blocking its entry into the cell. A
However, evidence is still unsure of the duration of these antibodies. A
A person who receives a vaccination develops active immunity for the disease the vaccine protects against. Vaccines allow the body to develop an immune response without requiring an infection. All vaccines currently in use produce high titers of neutralizing antibodies. However, a
A 2021 study estimating mRNA vaccine effectiveness among frontline and other essential workers indicate they are
In addition to being safer, evidence also suggests that immunity from vaccination produces a stronger and longer lasting immune response. Emerging evidence also
A 2021 study found that previously infected individuals retain immunological memory to SARS-CoV-2, with robust immunity up to
While there is not as much evidence on the duration of immunity from vaccines, a
Reports of reinfections are
Similarly, a report from the
This is consistent with a 2021 study that found those with more severe COVID-19 disease are likely to have a more robust immune response to SARS-CoV-2 and will likely have a higher level of protection from reinfection.
People can become immune to SARS-CoV-2 through adaptive immunity. This can be through either natural immunity or vaccine-induced immunity. While research is still ongoing, evidence suggests that both provide effective and long lasting immunity. With a high enough vaccination rate, it may still be possible to achieve herd immunity.
While it is still possible to acquire reinfection of the disease or a SARS-CoV-2 infection after a vaccination, adaptive immunity can still provide protection. It is advisable for people to continue practicing protective measures, such as hand washing, physical distancing, and wearing face masks.