This initially looked like a *gulp* moment, but might actually turn out to be the best news about the virus we’ve yet had. Over a month ago, researchers in South Korea sent out a warning that some previously infected and recovered COVID-19 patients had tested positive again. That prompted fears about the virus “reactivating,” which would have doomed vaccine and treatment efforts. Later studies suggested that the tests had malfunctioned by picking up dead viral matter, but the worries about immunity continued.

Now, a new study in South Korea on a much larger sample confirms that the patients testing positive have not been reinfected. Bloomberg reports that this actually confirms conferred immunity, and perhaps points the path back to normality:

Scientists from the Korean Centers for Disease Control and Prevention studied 285 Covid-19 survivors who had tested positive for the coronavirus after their illness had apparently resolved, as indicated by a previous negative test result. The so-called re-positive patients weren’t found to have spread any lingering infection, and virus samples collected from them couldn’t be grown in culture, indicating the patients were shedding non-infectious or dead virus particles.

The findings, reported late Monday, are a positive sign for regions looking to open up as more patients recover from the pandemic that has sickened at least 4.8 million people. The emerging evidence from South Korea suggests those who have recovered from Covid-19 present no risk of spreading the coronavirus when physical distancing measures are relaxed.

The results mean health authorities in South Korea will no longer consider people infectious after recovering from the illness. Research last month showed that so-called PCR tests for the coronavirus’s nucleic acid can’t distinguish between dead and viable virus particles, potentially giving the wrong impression that someone who tests positive for the virus remains infectious.

In practical terms, that means patients that have recovered from a certified diagnosis of COVID-19 infection need no further testing. Their bodies are killing COVID-19 effectively, which means they can go out in public without fear of reinfection, and without fear of becoming a COVID-19 carrier. As more and more people acquire the virus and produce the antibodies, the less transmissible the virus will become. In other words, it looks like herd immunity has a very good chance of standing up to COVID-19.

But for how long? Research in the UK has found that children turn out to be poor vectors for the disease, which is also good news. Only one outbreak has been documented at a school thus far, one expert testified, which means that school reopenings might not present nearly as much risk as first thought. However, John Edmunds questioned just how long conferred immunity might last:

John Edmunds, a member of Britain’s Scientific Advisory Group for Emergencies (SAGE), told the House of Lords’ science committee that it was striking how children did not seem to play much of a role in spreading the novel coronavirus.

“It is unusual that children don’t seem to play much of a role in transmission because for most respiratory viruses and bacteria they play a central role, but in this they don’t seem to,” said Edmunds, a professor at the London School of Hygiene and Tropical Medicine.

“There is only one documented outbreak associated with a school – which is amazing,” Edmunds said.

But he added there was potentially bad news, though, that human immunity to the novel coronavirus may not last long.

That will be the question of the year, no? We have a long experience with influenza and vaccines that make it pretty clear we only have limited time for immunity — because the virus keeps mutating, though. What about for non-mutating viruses? Bloomberg’s article notes that people exposed to SARS continue to produce “significant” levels of antibodies for nine to seventeen years, the latter of which is the length of time since its outbreak. It might be that many people produce immunity to SARS for a lifetime, which might explain why we’ve never had another major outbreak of it. Herd immunity and isolation may have killed it off for good.

Given the relation between SARS and COVID-19, that’s at least cause for hope. So too are the results from Moderna’s first-run trial of its vaccine candidate, former FDA commissioner Dr. Scott Gottlieb told CNBC’s Squawk Box this morning. There’s a lot of work to be done and more trials to do, but “it does show that this vaccine can produce an immune response.” If this vaccine can do it, then perhaps others will do the same. The bad news is that the Moderna test turned out to be only eight people, not 45, which means that there’s a lot of work left to be done indeed.