Last month I wrote about a Chinese study of the coronavirus which found antibodies to the virus only last a few months in the body. That seemed to indicated that people who’d survived the virus would not have a long term immunity to it. Over the weekend a pre-print (meaning it hasn’t been peer-reviewed yet) study from King’s College in the UK found something similar.

People who have recovered from Covid-19 may lose their immunity to the disease within months, according to research suggesting the virus could reinfect people year after year, like common colds.

In the first longitudinal study of its kind, scientists analysed the immune response of more than 90 patients and healthcare workers at Guy’s and St Thomas’ NHS foundation trust and found levels of antibodies that can destroy the virus peaked about three weeks after the onset of symptoms then swiftly declined.

Blood tests revealed that while 60% of people marshalled a “potent” antibody response at the height of their battle with the virus, only 17% retained the same potency three months later. Antibody levels fell as much as 23-fold over the period. In some cases, they became undetectable.

“People are producing a reasonable antibody response to the virus, but it’s waning over a short period of time and depending on how high your peak is, that determines how long the antibodies are staying around,” said Dr Katie Doores, lead author on the study at King’s College London.

There are several caveats here, starting with the fact that this hasn’t been peer reviewed yet. In addition, there are actually two distinct kinds of immunity in the body. Antibody immunity is also known as humoral immunity. But there is a separate type of immunity called cellular immunity which involved white blood cells called T-cells which target virus-infected cells. This study only looks at the former kind of immunity but there is some evidence that even people with low levels of antibodies have some T-cell immunity to the virus.

However, there is also some early concern that people are actually getting the virus more than once. Yesterday, Vox published a piece by a doctor named D. Clay Ackerly who believes one of his patients has had the virus twice in three months and the second time was worse:

“Wait. I can catch Covid twice?” my 50-year-old patient asked in disbelief. It was the beginning of July, and he had just tested positive for SARS-CoV-2, the virus that causes Covid-19, for a second time — three months after a previous infection.

While there’s still much we don’t understand about immunity to this new illness, a small but growing number of cases like his suggest the answer is yes.

Covid-19 may also be much worse the second time around. During his first infection, my patient experienced a mild cough and sore throat. His second infection, in contrast, was marked by a high fever, shortness of breath, and hypoxia, resulting in multiple trips to the hospital.

Recent reports and conversations with physician colleagues suggest my patient is not alone. Two patients in New Jersey, for instance, appear to have contracted Covid-19 a second time almost two months after fully recovering from their first infection. Daniel Griffin, a physician and researcher at Columbia in New York, recently described a case of presumed reinfection on the This Week in Virology podcast.

Why would a second infection be worse than the first? Dr. Ackerly points out that that is sometimes the case with dengue fever. Research has shown it can become more severe upon a second infection because antibody levels have dipped to a specific level. He links to this Stat News piece from 2017 explaining how that works:

Dengue is transmitted via the bite of mosquitoes that carry the viruses. It is an unpleasant disease that can cause high fever, severe headache, and joint and muscle pain. But in some people, it can also cause small blood vessels to leak, which can lead to failure of the circulatory system, shock, and death.

Severe disease can happen with any dengue infection but is more common on the second.

Harris and her colleagues found that when antibody levels fell to a certain point in children who had been previously infected, they were at greater risk of having severe dengue disease if they were again infected. In fact, for children whose antibodies fell to within this low range — a sort of anti-sweet spot — the risk was nearly eight times higher than for other children.

The belief is that low levels of antibodies cannot neutralize or kill the invading viruses. But they do bind to them and effectively usher them into susceptible cells, where the viruses then replicate.

This is still speculation at this point. Dr. Ackerly can’t even say for certain that his patient was infected a 2nd time (as opposed to one lingering infection). Still, the overall picture is pretty grim. If it turns out that immunity to the disease only lasts a few months then this is likely to become an annual disease similar to the common cold (which is also a coronavirus). We could be fighting new outbreaks of this every winter, unable to reach herd immunity naturally. If this latest study proves to be accurate then a vaccine may be our only real hope of returning the world to normal.

The first half of this report covers the new immunity study. The second half discusses another study which found that people who had survived the coronavirus often developed heart abnormalities they didn’t have previously. So the lasting effects of this disease may be very serious even for those who survive a first infection.