New cases of COVID-19 reinfection ‘suggest herd immunity may not be real’

New cases of COVID-19 patients getting reinfected are casting doubt on the possibility of herd immunity against the disease.

Clay Ackerly, a top internal medicine physician, argues in a new article that the experience of his patient who tested positive for COVID-19 twice, and similar cases, suggests that herd immunity could be “wishful thinking”.

Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of the disease from person to person unlikely.

It could be through vaccination or previous infections but provides a measure of protection for individuals who are not immune.

Cases of COVID-19 patients testing positive for the disease after initial recovery had raised concerns about the risk of spread, but the World Health Organisation (WHO) once said there are no instances of reinfection.

“From what we currently know—and this is based on very recent data—it seems they these patients are expelling left over materials from their lungs, as part of the recovery phase,” a WHO spokesman was quoted as saying in May.

But Ackerly said while much is still not known about COVID-19, “a small but growing number of cases” like his patient suggests people can contract the disease twice.

He said the patient, aged 50, tested positive for the novel coronavirus a second time — three months after a previous infection.

“Recent reports and conversations with physician colleagues suggest my patient is not alone,” he said, adding: “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.”

He, however, said “it is possible, but unlikely, that my patient had a single infection that lasted three months” as in the case of some COVID-19 cases who suffer persistent infections.

“My patient, however, cleared his infection — he had two negative PCR tests after his first infection — and felt healthy for nearly six weeks,” he said

“I believe it is far more likely that my patient fully recovered from his first infection, then caught Covid-19 a second time after being exposed to a young adult family member with the virus.

“He was unable to get an antibody test after his first infection, so we do not know whether his immune system mounted an effective antibody response or not.

“Also troubling is that my patient’s case, and others like his, may dim the hope for natural herd immunity,” he further said, listing out three signals from his patient’s experience.

“First, the trajectory of a moderate initial infection followed by a severe reinfection suggests that this novel coronavirus might share some tendencies of other viruses such as dengue fever, where you can suffer more severe illness each time you contract the disease.

“Second, despite scientific hopes for either antibody-mediated or cellular immunity, the severity of my patient’s second bout with Covid-19 suggests that such responses may not be as robust as we hope.

“Third, many people may let their guard down after being infected, because they believe they are either immune or incapable of contributing to community spread. As my patient’s case demonstrates, these assumptions risk both their own health and the health of those near them.”