More than half of Americans may have never had Covid, according to U.S. government data, leaving scientists wondering whether those who’ve avoided the novel coronavirus might actually be immune to the virus altogether. This could offer new clues into how to attack Covid.
At this stage in the pandemic, people may be immune due to vaccines, a past infection, or a combination of both. There’s also evidence that, in rare instances, some people may be Covid-immune without infection or vaccination at all.
The coronavirus’s frequent mutations and the fact that immunity wanes over time make it difficult to discern how many people are immune at any given moment. Studies have shown, for example, that while omicron infections offer some immunity against delta, omicron is able to circumvent antibodies from both past infection with other variants and vaccination. Current surveillance techniques have also likely vastly underestimated the number of cases, as more people are taking Covid tests at home and not reporting the results.
"It's nearly impossible to gauge protection," said Andy Pekosz, a virologist at Johns Hopkins Bloomberg School of Public Health.
As cases yet again rise in many regions more than two years into the pandemic, studying those who have not yet caught Covid has become just as critical as studying those who have. Experts say that people with so-called “super” immunity who appear resistant to the virus without vaccination may hold answers to important questions about why certain people get so sick while others don’t. Examining these cases could also help inform the development of vaccines and therapeutics less vulnerable to viral mutations.
“It is essentially defining what a best-case scenario looks like, which can also help to identify what is going wrong in those that don’t control the virus,” said Leo Swadling, an immunologist at the University College of London.
It may be hard to believe that at this stage of the pandemic so many people have still never gotten sick. Perhaps people were asymptomatic and never knew they were infected, or, despite exposure to the virus, they just never tested positive. But even half of the population getting Covid is actually an extraordinary number of infections. The 1918 Spanish flu is estimated to have only infected 25% of the U.S. population at the time, despite causing a huge number of deaths.
Early in the pandemic, Swadling set out to find out more about the lucky few who weren’t getting sick.
“We were particularly interested in people who are exposed to the virus, but control it very quickly, clearing the virus before it can replicate to detectable levels and before it induces an antibody response,” Swadling said. “It may help us better understand what immunity is best at protection from reinfection.”
Swadling, along with colleagues in London, published a study in the journal Nature last November evaluating a group of U.K. health care workers during the first wave of the pandemic. They found evidence that some of the health care workers exposed to the virus were able to rid their bodies of it even before producing Covid-specific antibodies.