From the beginning of the pandemic, there’s been a lot of focus on “antibody tests” that determine whether people have been infected with, and thus are likely immune from reinfection with, the virus. It’s starting to look like that focus was misplaced, or at least incomplete.

Some studies have suggested that other coronaviruses (such as the old SARS) might give people immunity to COVID-19 via T cells, another part of the immune system. And now a Swedish study hints that infection with COVID-19 itself sometimes creates T-cell but not antibody immunity.

The actual paper is dense with fancy science words I don’t understand (“acute phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype . . .”), but here’s some information from a press release:

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“Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in,” [says one of the paper’s authors] . . .

“One interesting observation was that it wasn’t just individuals with verified COVID-19 who showed T-cell immunity but also many of their exposed asymptomatic family members,” says Soo Aleman. “Moreover, roughly 30 per cent of the blood donors who’d given blood in May 2020 had COVID-19-specific T cells, a figure that’s much higher than previous antibody tests have shown.”

. . . Patients with severe COVID-19 often developed a strong T-cell response and an antibody response; in those with milder symptoms it was not always possible to detect an antibody response, but despite this many still showed a marked T-cell response.

This is a study of about 200 people that has not been peer-reviewed, so it might not hold up and its results might not generalize to other countries. But needless to say, the more people who are immune, the better, and if more people have been infected than we thought, the fatality rate is lower than expected.

Also worth reading: This piece from The Conversation on whether COVID-19 could burn out sooner than we thought.