Whether you’ve recovered from COVID-19, received the vaccine, or neither, understanding immunity and how long it lasts can help give you important insight into how you can interact safely with others during the pandemic.
First, it helps to know what immunity means.
There are two types of immunity: natural and vaccine-induced.
After a person acquires a virus, the immune system retains a memory of it.
The National Institutes of HealthTrusted Source explains, “Immune cells and proteins that circulate in the body can recognize and kill the pathogen if it’s encountered again, protecting against disease and reducing illness severity.”
The components of immunity protection include:
- Antibodies, which are proteins that circulate in the blood and recognize foreign substances like viruses, and neutralize them.
- Helper T cells help to recognize pathogens.
- Killer T cells kill pathogens.
- B cells make new antibodies when the body needs them.
People who recover from COVID-19 have been found to have all four of these components. However, specifics about what this means for the immune response and how long immunity lasts are not clear.
According to Lauren Rodda, PhD, a senior postdoctoral fellow in immunology at the University of Washington School of Medicine, we don’t know for certain if people are immune to reinfection simply because not enough studies have been done yet.
“This would require tracking the re-exposure of a significant number of people and determining if they get sick,” Rodda told Healthline.
Knowledge in this area continues to grow, however, as new studies are conducted.
Most recently, a study published in the journal Science has found that immunity can last for as long as 8 months.
According to Shane Crotty, PhD, a professor at the La Jolla Institute for Immunology in California who co-led the study, his team measured all four components of immune memory in almost 200 people who had been exposed to SARS-CoV-2, which causes COVID-19, and recovered.
The researchers found that the four factors persisted for at least 8 months following infection with the virus.
This is important because this shows that the body can “remember” SARS-CoV-2. If it encounters the virus again, the memory B cells can quickly gear up and produce antibodies to fight it.
Those who have recovered from COVID-19 could have immunity for months or perhaps even years, the authors said.
Before this latest study, Rodda said work had been done by her research team and others, showing that antibodies are maintained for at least 3 months.
In her team’s study, in particular, it was shown that this occurs even in people who have mild symptoms.
Their study also suggested that immunity could last much longer.
In a different study published in The New England Journal of Medicine, researchers in Iceland studied 1,107 people who had recovered from COVID-19 and tested positive for the antibodies.
Over a 4-month period, they found that those COVID-19 antibodies did not decline.
A study published in the journal Immunity found that people who recover from even mild cases of COVID-19 produce antibodies for at least 5 to 7 months and could last much longer.
Their team has tested nearly 30,000 people in Arizona since April 30, 2020, shortly after a blood test for the new coronavirus was developed.
Currently, the two vaccines authorized for useTrusted Source in the United States are from Pfizer-BioNTech and Moderna. The Moderna vaccine is about 94 percent effective at preventing COVID-19, and the Pfizer-BioNTech vaccine is 95 percent effective.
Both vaccines workTrusted Source by helping the body develop immunity to the virus that causes COVID-19 without you having to get COVID-19.
Both vaccines require two shots a few weeks apart to get full protection.
Once you have full vaccine protection, your body is left with a supply of T cells as well as B cells that will remember how to fight the virus in the future, just like they do with natural immunity.
However, it usually takes a few weeks for the body to produce T cells and B cells after vaccination. During this time, it’s possible to acquire the virus that causes COVID-19 until your body can provide protection.
In a Q & A with the World Health Organization (WHO), Dr. Katherine O’BrienTrusted Source, professor at Johns Hopkins Bloomberg School of Public Health, said, “We see a good immune response that kicks in within about two weeks of that first dose. And it’s really the second dose that then boosts that immune response, and we see immunity get even stronger after that second dose, again within a shorter period of time after the second dose.”
Researchers still don’t know how long immunity lasts from the vaccines and if follow-up shots will be needed, especially to protect against new variants of the COVID-19 virusTrusted Source.
Studies are underway.
The Centers for Disease Control and Prevention (CDC) states that “nearly all immune-competent individuals will develop an immune response following SARS-CoV-2 infection,” and that in some people, antibodies can be detected within the first week of illness onset.
However, there are different antibody testsTrusted Source, and they each detect different components of immunity protection mentioned above.
For instance, some tests look for antibodies that recognize the protein nucleocapsid, which is found in the coronavirus, while others look for antibodies that protect against the coronavirus spike protein (these antibodies are triggered by the Moderna vaccine.)
While a positive antibody test shows that you had the virus that causes COVID-19 or the vaccine, it still doesn’t give a clear understanding of your immunity to the virus.
Dr. Steven Sperber, interim chief of the division of infectious diseases at Hackensack University Medical Center, said that he does not know if having a positive antibody test means you’re immune to the virus.
He explained that, for some infections, antibodies might protect against reinfection.
For others, they may not prevent reinfection, but symptoms may be milder.
In yet other cases, antibodies may provide no protection at all.
Also, some test results may be “false positives.” This occurs when a person has been exposed to a similar virus detected by the test, but those antibodies don’t protect the new coronavirus.
Finally, Sperber said, we don’t know how long any protection might last.
However, a studyTrusted Source published on February 24, 2021 in the journal JAMA Internal Medicine, found that people who tested positive for SARS-CoV-2 antibodies based on commercial antibody tests may be at decreased future risk of SARS-CoV-2 infection.
The study looked at data of more than 3.2 million people in the United States with a SARS-CoV-2 antibody test. Researchers evaluated evidence of SARS-CoV-2 infection among people with positive versus negative test results for antibodies.
Researchers noted that while the risk reduction was not seen in the first 30 days after an initial antibody test, it became pronounced after 30 days and progressively strengthened through the 90-day observation period and beyond.
Cases of reinfectionTrusted Source with the new coronavirus have been reported but remain rare, according to the CDC.
Though infection with the virus and getting vaccinated can provide some immunity, it is still not fully understood for reinfection.
Studies are in the works to understand:
- the likelihood of reinfection
- how often reinfection occurs
- how soon after the first infection can reinfection take place
- how severe cases of reinfection are
- who might be at higher risk for reinfection
- what reinfection means for a person’s immunity
- if a person is able to transmit SARS-CoV-2 to other people when reinfected