Covid-19: Relapse of infection a new concern

NEW DELHI: While the government continues with tests, isolation and treatment of covid-19 patients, a new concern has surfaced -- relapse of infection among those cured of the disease. Since not much is known about the behaviour of the virus, a few such cases in India have left doctors perturbed.

A 59-year-old Philippine national, who had been admitted to Kasturba Hospital in Mumbai on 13 March with symptoms, later died at Hiranandani Hospital. He had tested positive for covid-19 but had later tested negative in two subsequent tests after treatment, which the state government said proves that he recovered from the infection. He died due to underlying conditions including diabetes and asthma. The state government had said his death cannot be linked to the covid-19 infection.

Similarly, a patient in Delhi first tested positive, was treated, and then tested negative and later died.

Scientists have warned that if the immune system of the cured patient is weak, there is a likelihood of relapse. “Generally, an infection gives immunity to re-infection. This is based on the production of neutralizing antibodies and is the central pillar of how a vaccine works,” said Lalit Kant, scientist and former head of epidemiology and communicable diseases at the Indian Council of Medical Research (ICMR).

“Re-infection in Covid-19 is unlikely, but you cannot rule it out, as we have not understood the human immune response fully. There are several unanswered questions,” said Kant. Health experts claim that if person who was positive for covid-19 recovered and tested negative. After a variable period of time the person develops symptoms and tests positive again, there are several possibilities.

“The test done to say that person has recovered was false negatives. It means that the test was negative when actually the person was not clear of the virus. False negatives have been reported in RT-PCR. Re-testing is always advisable in such cases,” said Kant.

“In some persons the virus persists for a longer period – may be several weeks- resulting in a positive test even after several weeks,” said Kant adding that it could be that the virus was more concentrated in the deeper parts of the respiratory system and upper respiratory tract specimens such as nasal or throat swabs could have a lower viral load and could result in false-negative tests among the mild cases.

Kant explained that immunity build-up depends upon the virus and the host. A weak immune system produces weak immunity. “There may be a second strain of virus which is immunologically different from the strain causing the pandemic. But Covid-19 is not a rapidly mutating virus – giving hope that immunity or the vaccine would give long lasting protection,” said Kant.

“Even if there was a re-infection my guess is that the earlier infection would give rapid immunity and the person should recover quickly. Some infections produce immunity that is short lived. Over time, the immunity fades away. Like in SARS infection there are indications that it starts to wane in about 2 years’ time,” he said.

Public health experts have said covid-19 is unique and complex. While those who have been infected with covid-19 develop a protective antibody, it’s not clear how long the protection lasts.

“Government and Public Health Managers are very much aware of this possibility and the government discharge policy for covid-19 cases requires discharge after only two samples test negative within 24 hours and there’s evidence of chest radiographic clearance and viral clearance in respiratory samples,” said Himanshu Sikka, chief strategy and diversification officer, Health, Nutrition and WASH, IPE Global, an international health consultation company.

According to the union health ministry, post discharge as well there is a requirement to self-quarantine for another 14-day period. “If these guidelines are followed, then while the likelihood of re-infection doesn’t get reduced, it still ensures that there is no further spread of the virus,” said Sikka.