After recovering from a viral infection, the human body’s immune system retains a memory of the virus so that if the person encounters it again, their immune system will be able to recognize and kill the pathogens. Although a healthy immune system is remarkably effective at protecting the body from outside invaders, until recently researchers did not understand many details about COVID-19 immunity after infection. For how long are people immune to SARS-CoV-2 after recovering from COVID-19? Is this immunity comparable to the level of protection provided by a COVID-19 vaccine?
According to new studies, recovery from a COVID-19 infection does provide immunity for several months. However, it’s important to keep in mind that previously infected people can still carry and transmit the virus to other people.
Research from the National Cancer Institute
After examining hundreds of Americans, researchers from the National Cancer Institute found that the risk of contracting COVID-19 within three months was about 90 percent lower for those who had been previously infected. The level of protection provided by COVID-19 immunity after infection appears to be comparable to the protection offered by the Pfizer-BioNTech and Moderna vaccines, which reduce the risk of developing COVID-19 by at least 94 percent for three months following immunization. As the researchers noted, the protection offered by a vaccine is decidedly preferable to immunity caused by a natural infection, as authorized and approved vaccines don’t carry risks as severe as those presented by natural infections.
Research from Public Health England
According to a study by Public Health England (PHE), people who have been infected with COVID-19 previously are likely to be protected against reinfection for several months. The researchers tested thousands of healthcare workers in the United Kingdom for new COVID-19 infections and the presence of antibodies. They concluded that COVID-19 immunity produced by a previous infection provides 83 percent protection against reinfection when compared to those who have not had COVID-19, and the immunity appears to last at least five months on average.
The PHE researchers warned that people with COVID-19 antibodies can still carry the virus and transmit it to others, so it is important that they continue following health and safety guidelines. These people should continue social distancing, wearing a mask, washing their hands regularly, etc. to reduce their likelihood of carrying and circulating the virus.
To continue exploring how long COVID-19 immunity may last, the PHE study will follow participants for 12 more months. The researchers are also examining the effectiveness of COVID-19 vaccines and the extent to which people with COVID-19 immunity are able to carry and transmit SARS-CoV-2.
Research Led by Scientists from La Jolla Institute for Immunology
After analyzing 200 people who had been exposed to SARS-CoV-2, a team of researchers led by scientists from La Jolla Institute for Immunology found “durable immune responses” in the majority of participants. Antibodies were found in 98 percent of participants a month after the onset of symptoms. Although the number of antibodies varied widely between participants, the antibodies remained relatively stable over a period of months. In fact, the levels of antibodies in participants only decreased by a small amount six to eight months after infection.
These three studies suggest that the immune system produces durable immunity following COVID-19 infection. Although we don’t yet know exactly how long this immunity lasts, this research is providing further hope in the fight against COVID-19.
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