© Simon Dawson/Bloomberg
Test tubes to be used for blood samples sit on a table at an antibody testing program at the Hollymore Ambulance Hub in Birmingham, U.K., on June 5. (Simon Dawson/Bloomberg)
When a coronavirus outbreak on a Seattle trawler in May infected more than 100 crew members, three fishermen with antibodies were spared, according to a new study, providing encouraging evidence about our immunity from the contagion.
The study, which published Friday and has not been peer-reviewed, offers hope that antibodies can offer protection against infection. But the research about the fishing boat’s outbreak has a catch.
While scientists say the study will help us understand how antibodies thwart the coronavirus infection, they caution that the presence of antibodies doesn’t definitively guarantee immunity. Researchers are still trying to understand what immunity to the coronavirus will look like and, despite the successful University of Washington study, much remains to be seen.
Even as a stream of new immunology research is published about the novel virus, mysteries remain unsolved about how people like the fishermen are able to remain safe from the grips of covid-19, the disease caused by the virus. The Washington Post received hundreds of questions from readers about immunity from the virus, from what will it take to reach herd immunity to how virus mutations may affect people’s immune responses. We posed several of these queries to researchers, and here’s what we found out.
How does coronavirus immunity work?
Immunologists say coronavirus patients’ immune responses mostly track with other viral illnesses like the flu.
To protect against viruses, the human body has a multi-attack immune arsenal it deploys. The first defense is T cells, specialized white blood cells that remember the virus, blood proteins that neutralize infection. However, the presence of antibodies doesn’t mean someone is impervious to infection.
“It’s not black and white, like you’re immune or not immune,” Sarah Fortune, the chair of immunology and infectious diseases at Harvard University’s T.H. Chan School of Public Health, told The Washington Post. “There are gradations of immunity.”
While antibodies can wane in the weeks after infection, longer-lived B cells, which produce antibodies, continue to fend off infection over time.
“Your immune response is generally wired to ramp up when the danger is high, and then be able to wind things down when the danger has passed,” Fortune said.
However, the presence of antibodies in the three fishermen on the American Dynasty vessel who skirted the outbreak indicates that their body had built a defense against the coronavirus, possibly from a previous infection.
Those three were the only people with antibodies aboard the ship out of 122 people who had let scientists collect blood samples before they set sail. After 18 days at sea, the virus had swept across 85 percent of the boat’s crew but did not sicken those three, hinting at immunity, researchers wrote.
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How long are the body’s defenses against the virus effective?
The Centers for Disease Control and Prevention inadvertently stoked reports last week that covid-19 patients had months of immunity when it shared updated guidance that advised people to not seek a test for three months after they have recovered from the coronavirus.
However, the agency later clarified its advice, saying it was about how retesting can lead to false positives.
“Contrary to media reporting today, this science does not imply a person is immune to reinfection with SARS-CoV-2, the virus that causes covid-19, in the 3 months following infection,” the CDC wrote in a statement. “The latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of covid-19 and the symptoms cannot be associated with another illness.”
The CDC advises people who recover from the coronavirus to still social distance and wear face masks, as researchers learn how effective antibodies are at warding off infection.
Scientists discovered the body’s defenses against the coronavirus — antibodies, T cells and B cells — appear to persist for three months past when the infection has run its course, even among patients with mild cases, according to a separate University of Washington study published Saturday.
After research had indicated that antibody counts of those who recovered could drop off in months, some speculated that immunity to the virus may be short-lived. But immune systems also produce fewer antibodies when they aren’t under viral attack, immunologist and co-author Lauren Rodda said.
Rodda and other researchers counted the B and T cells that produce antibodies and found the numbers remained stable or increased.
“It shows that the immune system is working as it should be,” Rodda said.
As scientists hope to figure out how these cells could protect against reinfection from the coronavirus in humans, recent research of rhesus monkeys has shown that primary exposure to the coronavirus offered protection against reinfection or serious illness.
“These studies showing primary infection is actually protective, at least in monkeys, is starting to build this very promising story about people being immune at least three months, probably longer but we just don’t know yet,” Rodda said.
Is herd immunity possible?
If there is hope that reinfection is unlikely, that raises the question: How many cases will it take until the country can develop herd immunity?
There isn’t a consensus of when the United States may reach herd immunity — the point when a large portion of the population is immune, making it harder for the virus to circulate widely. Estimates for the coronavirus range from 40 to 80 percent.
But public health experts including Trevor Bedford, a scientist at Fred Hutchinson Cancer Research Center in Seattle, caution that people should try to continue social distancing and mask-wearing to prevent the spread of the virus.
While the “substantial outbreaks in Arizona, Florida and Texas” provided great immunity, “the costs for this immunity have been substantial and are continuing to accrue,” Bedford tweeted. “We need a vaccine to achieve population immunity in a fashion that doesn’t kill people.”
Herd immunity may be brought about by the advent of a vaccine, but some viruses that have available vaccines, such as measles, can still infect people.
“If you have large proportions of the population infected, it’s very hard for the virus to spread, but it might find niches where it can spread,” Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York told The Post. “So it’s very unlikely we’ll ever get rid of SARS-CoV-2.”
Like the flu, will people need to get a coronavirus vaccine annually?
When a vaccine becomes publicly available, researchers aren’t yet sure how effective it will be against protecting people from coronavirus over time.
The vaccine for the flu is new every year. But the mutating process for influenza is wholesale, meaning it swaps out larger portions of its genes, compared with the coronavirus, Fortune said.
Since the novel virus doesn’t change at the same cadence as the flu, people may only need to be vaccinated once — or possibly receive an immunization and booster shot.
Fortune compared the vaccine selection to dating prospects: “Nobody is perfect, but you’re just choosing the characteristics you like best.”