What the HK reinfection case means
NEW DELHI: Researchers in Hong Kong said they have the first evidence of a repeat infection of Covid-19, a claim that the scientific community has described as both unsurprising, and worth looking into. Experts have said that since this study involved a singular case, more research is needed to establish the findings although there is some consensus on what has been established and what it could mean.
THE CASE
In late March, a 33-year-old Hong Kong resident contracted Covid-19 and was symptomatic. The man was hospitalised and deemed recovered on April 14. Genomic analysis showed the infection was with a strain prevalent in Asia at the time
On August 15, the patient – while on his way back from
Spain – tested positive for an infection at the Hong Kong airport. He did not have any symptoms. Analysis of the genome showed this was an infection by Sars-Cov2 of a different lineage -one now prevalent in Europe
ANTIBODY QUESTION
The researchers note that the first infection triggered antibodies that tapered off and were undetectable during the second reinfection. Neutralising antibodies are responsible for binding to free virions, inhibiting their ability to infect cells. These usually taper off after an active infection is resolved.
“This is no cause for alarm this is a textbook example of how immunity should work,” said Akiko Iwasaki, professor of immunobiology at Yale School of Medicine in one of a series of tweets. A drop in these implies a person’s immune system may not be able to stop a second infection. It is possible, as several studies have suggested, that another side of the immunity that forms a memory of a pathogen may help quickly create antibodies and other responses upon a second infection, which could help the person have a mild or asymptomatic illness.
The researchers note as much, saying” “residual low titer of antibodies may have partially controlled the virus”.
INFECTED = INFECTIOUS?
The researchers note that the purported second infection showed high viral load that tapered off with time, all the while with the person being asymptomatic. High viral load has previously been linked with an increased likelihood of a person being infectious, even when they have no symptoms.
RESEARCHERS SAY THE CASE HAS SEVERAL IMPLICATIONS WITH THE FIRST CHALLENGING POPULAR NOTIONS ABOUT NATURAL HERD IMMUNITY AND ANOTHER LINKED TO VACCINES
HERD IMMUNITY QUESTION
This case, the researchers say, has several implications with the first challenging popular notions about natural herd immunity. “It is unlikely that herd immunity can eliminate Sars-Cov2, although it is possible that subsequent infections may be milder than before,” the report. The virus thus could become similar to several seasonal coronaviruses that infect humans, becoming part of the typical flu season.
IMPLICATIONS FOR VACCINES
Noted virologist Jacob John told HT last week that natural infections cannot be seen in the same manner as vaccine-triggered herd immunity.
“It does not work in the same way because a vaccinated person does not spread the disease, while an infected person passes it on to others in the initial days at least,” he said.
This possibly leaves vaccines as the most important tool in efforts to stop the pandemic. “The only safe and effective way to achieve herd immunity is through vaccination,” wrote Iwasaki in a second tweet.
The researchers said in their study, submitted to the Clinical Infectious Diseases journal, say that vaccine studies should include patients recovered from Covid-19, and that ultimately, vaccines may not offer lifelong immunity.