How long will immunity to COVID-19 last once a person is infected?
For the first time we are hearing recovered COVID-19 patients have immunity from getting infected again for up to seven months.
And if history repeats itself, that time could grow.
After an initial infection, patients who had the first SARS virus in the early 2000s showed immunity 17 years later. In those infected with MERS in 2012, studies show similar long-term protection.
But will SARS-CoV-2 follow the same pattern? For most people this is going to be many months, probably several years.
To find scientific proof, researchers at University of Arizona Health developed a test that detects early and later stage antibodies in two separate parts of the virus, including those that appear during the body’s second wave immune response. Plasma cells stick around for a longer period of time and appear to offer long-term immunity.
Earlier studies suggested antibodies drop off within three months, providing only short-term immunity, longer term studies proved that was not the case.
Dr. Janko Nikolich-Zugich, MD, PhD is a professor and head of the Department of Immunobiology at University of Arizona Health.
“Not in the very beginning but around a month to two months, we make these cells that are with us for a very long time and they can produce a lot of antibodies for a very long time,” he said. “The antibodies, when we make them, don’t really go away particularly if the virus is dangerous.”
Beginning in April, the team tested nearly 6,000 people who had COVID-19 in Pima County, Arizona.
“We measured immunity for as long as we could, which is after seven months. And we really did not see any evidence of it going down,” Nikolich-Zugich said
And their research continues. They’ve now tested more than 30,000.
Closer to home at Northwestern University, Dr. Thomas McDade and his team are conducting a similar study. They are distributing their in-house developed test in Chicago areas known to have high rates of COVID-19. The results showed even more people had COVID antibodies than doctors or patients knew.
“In our early analysis preliminary results suggest that about 20 percent of people in our study test positive for exposure for the virus, which is interesting. It’s higher than we would have anticipated,” McDade said.
Of the 1,000 people enrolled so far in Northwestern’s scan study, only 2 percent reported they had actually tested positive for SATS-CoV-2. And their levels of antibodies were much higher compared to other participants. And while the scan study is designed to investigate a variety of issues surrounding COVID-19 prevalence and transmission, McDade said determining long-term immunity will be a key data point, particularly among those who never got symptoms but did carry antibodies.
“It might be that those people are immune moving forward or relatively immune moving forward, but it also may mean they just didn’t get exposed to enough of the virus to mount a rigorous and long-lasting immune response,” McDade said. “And upon subsequent exposure, they may be susceptible to infection again. We just don’t know. Only time will tell.”
“The probability of reinfection is less than 0.01% so it’s very small,” Nikolich-Zugich said.
There have been five confirmed cases globally, including one in the U.S.
“Either these people have some level of immune deficiency that was not diagnosed before, or maybe they have gotten just a tidbit of the virus,” Nikolich-Zugich said.
There is more potentially good news today about infection from the World Health Organization. While SARS-CoV-2 is mutating and becoming more easily spread, the new version is not making people as sick.
To learn more about Northwestern’s SCAN study visit Scan.northwestern.edu