• A new study from the UK indicates that coronavirus immunity can last for up to 5 months after infection. The researchers plan to follow the participants for up to 12 months to determine a more accurate estimate.
• The study also offers a key finding that was previously unaddressed in COVID-19 research. People who acquire coronavirus immunity after being infected can still contract the virus without experiencing COVID-19 symptoms and then infect others. 
• As immune people could carry the virus in their nose and throat, it’s crucial for people to continue respecting health measures even after beating COVID-19.

The novel coronavirus is still spreading ferociously in several countries that are experiencing a new record wave of infection. Some local epidemics are fueled by new mutations that are highly infectious, like the UK, South Africa, and even Brazil. And the US hasn’t flattened the ongoing winter curve either, with infections reaching record highs in early January. The virus is transmitted via droplets and aerosols, which are ejected during coughing, sneezing, and even talking. Touching contaminated objects is also a theoretical infection risk if your hands aren’t clean when you touching your face. People can spread the virus a few days to a few weeks after contracting it, and they’re usually contagious a few days before the onset of symptoms.

That’s why face masks, social distancing, frequent hand washing, and indoor space ventilation are vital for reducing transmission. And now, a brand new study from the UK delivers a key piece of information that should further help authorities combat the pandemic. Even if you already had COVID-19, you can still catch it and infect others.

A new Public Health England (PHE) study looking at COVID-19 immunity offered its first round of conclusions. Scientists say that people who have survived COVID-19 might be protected for at least five months. That’s in line with other recent studies, and the estimate grows as time passes. But that’s not the most important takeaway from the research. The SIREN scientists warn that people who have gained immunity after exposure to SARS-CoV-2 can still contract the virus. The pathogen can multiply in the nose and throat. While they might not experience any symptoms, they could still be infectious to others, even though they might not think that would be the case.

This isn’t the first time we’ve been told of this possibility. Discussing Phase 3 vaccine results and expectations for the near future, Moderna said in a recent interview that people who are immunized might still contract the virus and infect others, even without symptoms. That was only a hypothesis at the time. The first generation of vaccines isn’t supposed to prevent infection. The main goal is to prevent COVID-19 complications and reduce the risk of death.

But the SIREN study makes it clear that infection from a COVID-19 survivor is a possibility that everyone should be aware of. The conclusion will come after the next stage of the study, so we don’t have measurable statistics yet. Still, the finding underscores the importance of respecting health measures even after surviving COVID-19 or receiving a vaccine.

“This study has given us the clearest picture to date of the nature of antibody protection against COVID-19, but it is critical people do not misunderstand these early findings,” Professor Susan Hopkins said in a statement. Hopkins is a senior medical advisor at PHE, and the SIREN study lead researcher. “We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection, but this is not total, and we do not yet know how long protection lasts,” she said. “Crucially, we believe people may still be able to pass the virus on.”

“This means even if you believe you already had the disease and are protected, you can be reassured it is highly unlikely you will develop severe infections, but there is still a risk that you could acquire an infection and transmit to others,” the researcher said. “Now more than ever, it is vital we all stay at home to protect our health service and save lives.”

The SIREN scientists performed regular antibody and PCR tests on 20,787 healthcare workers across the UK since June. Of those, 6,614 tested positive for COVID-19 antibodies upon recruitment. The researchers identified 44 potential reinfections in this category, including 2 “probable” and 42 “possible.”

The 2 probable reinfections experienced COVID-19 symptoms in the first wave but were not tested via PCR. The second time around, the symptoms were less severe. None of the 44 got PCR tests in the first wave, but they all had COVID-19 antibodies when they were recruited.

If all 44 cases were confirmed, then the rate of protection from reinfection would be 83%. If only the 2 cases were confirmed, the rate would be 99%. More research is needed to clarify the percentage.

The SIREN researchers have concluded that the antibody protection after infection lasts at least five months. People who were infected in the previous wave might be vulnerable again if the immunity doesn’t last longer than 5 months. The scientists plan to continue studying the participants to see how long immunity lasts, analyze the effectiveness of vaccines, and determine to what extent the people with immunity can infect others. The researchers also note that the conclusions apply to the coronavirus version preceding the UK mutation (VOC202012/01 or B.1.1.7) confirmed in mid-December. A future version of the study will also take the mutation into account.