Coronavirus infection unlikely to strike twice
Scientists this week confirmed a new coronavirus reinfection in a 33-year-old man in Hong Kong, who had Covid-19 in March and was found to be infected by a different variant of the virus after 142 days during a visit to Europe. They used genetic sequencing to confirm that the second infection was caused by a genetically distinct virus from the one that caused the first infection in March.
The man, who is otherwise healthy, had developed cough and sputum, and was down with sore throat, fever and headache for three days when he first tested positive for Covid-19, but remained asymptomatic when he got reinfected in August, according to the study published in the journal, Clinical Infectious Diseases.
The study reignited the debate on whether true reinfection can occur. Studies show that following infection with Sars-CoV2, the virus that causes Covid-19, the infected person produces neutralising antibodies rapidly, but the antibody titers (count) begin to decline in about one to two months after acute infection.
But prolonged low-grade viral shedding detectable by reverse transcription-polymerase chain reaction tests has led to people testing positive weeks after recovering. In the past, recovered people tested positive again after a few weeks in South Korea, China and some European countries raising fears of re-infection, but scientists clarified that the repeat positive tests picked up dead viruses from past infection that did not make the person ill or infected others.
The genetic confirmation in Hong Kong proved a second infection can occur, but there are no reports of people developing symptoms or falling sick the second time.
“We are now beginning to see cases of re-infection, but till now we have not had a true re-infection where a person was symptomatic the first time, and symptomatic the second time. We only have cases of symptomatic the first time, and asymptomatic the second time. True reinfection with a patient who is twice symptomatic has not yet occurred,” said Dr Anurag Agrawal, director, Council of Scientific and Industrial Research-Institute of Genomics and Integrative Biology.
The immune system uses specificity, diversity, and memory to fight infection. The immunological memory involving T and B cells in the immune system lead to an adaptive antibody response that is faster, of higher affinity, and results in the secretion of non-IgM isotypes of IgG that give longer lasting protection against re-infection.
“So even as neutralising antibodies bind to the virus to immobilise it and T-cells battle with it, the memory B and T cells in immune system store recognition patterns of the virus for future reference. The neutralising antibody levels may decline in three months, but new infection is instantly recognised by the memory B cells that leads to the rapid deployment of the specific immune response pre-programmed to attack Sars-CoV2. So while it may not prevent reinfection, it will prevent damage to the body,” said Dr K Srinath Reddy, president, Public Health Foundation of India.
The amount of live virus in the nose and throat drops significantly soon after Covid-19 symptoms develop, with the duration of infectiousness in most people not lasting more than 10 days after symptoms begin, and 20 days on average in people with severe illness or those who are severely immunocompromised, according to the US Centers for Disease Control and Prevention.
A person who has recovered from Covid-19 may have low levels of virus in their bodies for up to three months after diagnosis. “This means that if the person who has recovered is retested within three months of initial infection, they may continue to have a positive test result, even though they are not spreading Covid-19,” said the latest CDC advisory.
The only protection is wearing masks, social distancing and hand hygiene. “Many people are not using the social vaccine and are not taking precautions, such as maintaining social distancing and wearing masks. People take out masks when they are speaking, eating, or having a conversation, which is the worst thing that can happen in terms of potential exposure to infected droplets,” said Dr Shiv K Sarin, director, Indian Institute of Liver and Biliary Sciences, New Delhi, which set up the country’s first convalescent plasma bank for treatment.
“There is no need to take off masks while speaking. Doctors, nurses and healthworkers routinely communicate through masks and PPEs (personal protective equipments), including during critical surgeries where miscommunication is not an option,” said Dr Reddy.
Since the disease is a little over eight months old, it’s still not known how strong and long-lasting protection antibodies provide, but testing for them is helping track the scale of the pandemic, understand the spread of infection. “The next survey in Delhi will tell us the quiet exposure in the population. The last sero-surveillance found close to 30% people have antibodies against Sars-CoV2 in Delhi, though we don’t know how protective these antibodies are as they are not neutralising, which offer longer protection,” he said.
“With opening up (after lockdown), cases will keep rising. I have a feeling in the next survey, we may be 38% or so positive in Delhi. The only way to protect people is to wear a mask, and wear it properly covering our nose and mouth,” he said.