So much has changed since the first cases of the coronavirus emerged earlier this year, with masks and social distancing now becoming the norm of everyday life (or they should be, anyway). But perhaps the most fluid part of the pandemic has been in trying to understand and predict the virus’ life span to begin with.
“This is such a complex disease that even immunologists can’t fully know everything about it,” said Christine Bishara, an internal medicine physician and founder of From Within Medical in New York.
One of the areas that’s been confusing most recently is Covid-19 antibodies ― proteins found in the blood that signal if you’ve had a past infection and therefore have built up immunity from the virus. Here, experts explain how the knowledge around antibodies has changed, how accurate tests are and what the latest research behind antibodies tells us about a future vaccine.
Antibodies do disappear, but it’s completely normal
“When our body is exposed to a virus, it goes through a very complex immune response, which includes different types of cells including B cells and T cells,” Bishara said. T cells help regulate the activity of B cells, while it’s the B cells that produce the antibodies that attach to cells that have been infected by a virus.
However, these antibodies take time to appear once you’ve been infected with any virus, including the coronavirus.
“It typically takes one to three weeks to see antibodies,” said Steven Schnur, a cardiologist and internist at Mount Sinai Medical in Miami and founder of Imhealthytoday.org, a doctor-designed programme for helping workplaces reopen from the pandemic safely. “Once they do appear, antibodies tend to wane after three months.”
But this doesn’t mean that once antibodies start vanishing you’re no longer immune to the coronavirus. That’s because those B cells and T cells that have been created in response to the virus have long-lasting memory and immunity, regardless of what your antibody levels drop to, Schnur said.
Many who may have been ‘reinfected’ with coronavirus likely never recovered in the first place
Right now, experts say it’s pretty unlikely that you can catch the virus again after you’ve recovered.
“There are a lot of anecdotal stories, but research has not found any individuals that have been truly reinfected,” Schnur said. “When people get sick again after six weeks or two months it’s really the same virus and same initial infection that has lingered longer than 10 days.”
Viruses can tend to be dormant for a bit, which can make them more drawn out symptomatically, Bishara added. This is supported even further in the characteristics behind those T cells and B cells.
“When the body generates an immune response [to a virus], T cells remember in case of a possibility of future reinfection, so that if presented with the virus again your body recognises it and knows how to handle it,” Bishara said.
Antibody testing seems like a good idea in theory, but may not be entirely accurate
There are a few flaws in antibody testing that are now coming to light. First, there were a number of antibody tests that shipped to labs and medical offices in the US without any review from the US Food and Drug Administration. Results of the tests varied, making it impossible to confidently tell patients whether they had antibodies.
But even antibody tests currently on the market aren’t as accurate as the medical community would like to see.
“A majority of antibody tests are checking for B cell types, specifically the antibodies immunoglobulins G (IgG) and M (IgM),” Bishara said. “Those are the ones that usually appear after an infection, but they take some time to do so. Part of the problem comes from when an antibody test is given, because if the body hasn’t developed these antibodies yet, the test may come back as a false negative.”
Those who are asymptomatic may also have an issue when it comes to testing because the body isn’t launching as big of an immune response as someone who presents with more severe symptoms. A small study from China published in the journal Nature Medicine found that 40% of patients who were asymptomatic or had very mild symptoms and tested positive for the virus did not show any antibodies in the blood.
“For someone to think that they can walk around without proper precautions because they have antibodies is inaccurate,” Schnur said. “Whether or not you think you have antibody levels, you still need to social distance and wear a mask.”
However, if you’re still set on getting an antibody test, Schnur recommends one done as a finger stick (and double-check that it’s not on the FDA’s “removed” list). If you get a positive test, do another one at a different lab to confirm.
“Only if you have two positive results from two different labs is the positive predictive value over 90 or 95%,” he said.
Decreased antibody levels in the body won’t affect the efficacy of a vaccine
Vaccines in general have a sliding scale of longevity depending on the type of disease it’s for, Bishara said. Diseases like smallpox and polio have been essentially eradicated with a single vaccine dose, while the flu vaccine is required every year. Just because the coronavirus antibody levels may decrease over time doesn’t mean a vaccine won’t be effective. It all comes down to whether the virus is able to mutate.
“When it comes to the flu, someone may still get the flu even if they’ve gotten their flu shot because of its ability to change,” Schnur said, “though that person may not suffer symptomatically the same as someone who didn’t get the vaccine at all.”
Since the coronavirus is still so new, it’s impossible to know how much it will modify itself. But Schnur said as of right now it looks like it doesn’t mutate as fast or as often as something like influenza, meaning a vaccine would be effective longer.
“A vaccine may not give us lifetime immunity, but it will probably last several years,” he said.