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Last Updated : Oct 14, 2020 03:11 PM IST | Source: Moneycontrol.com

Exposure to COVID-19 does not guarantee immunity, reinfection causes more severe symptoms, finds Lancet study

A study published in The Lancet Infectious Diseases journal charts the first confirmed case of COVID-19 reinfection in the United States and indicates that exposure to the virus may not guarantee future immunity

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COVID-19 patients may experience more severe symptoms the second time they are infected, according to research released on October 13, confirming it is possible to catch the potentially deadly disease more than once.

A study published in The Lancet Infectious Diseases journal charts the first confirmed case of COVID-19 reinfection in the United States — the country worst hit by the pandemic — and indicates that exposure to the virus may not guarantee future immunity.

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The patient, a 25-year-old Nevada man, was infected with two distinct variants of SARS-CoV-2, the virus that causes COVID-19, within a 48-day time frame. The second infection was more severe than the first, resulting in the patient being hospitalised with oxygen support.

COVID-19 Vaccine

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How does a vaccine work?

A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

How many types of vaccines are there?

There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

What does it take to develop a vaccine of this kind?

Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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The paper noted four other cases of reinfection confirmed globally, with one patient each in Belgium, the Netherlands, Hong Kong and Ecuador.

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Experts said the prospect of reinfection could have a profound impact on how the world battles through the pandemic. In particular, it could influence the hunt for a vaccine — the currently Holy Grail of pharmaceutical research.

"The possibility of reinfections could have significant implications for our understanding of COVID-19 immunity, especially in the absence of an effective vaccine," said Mark Pandori, for the Nevada State Public Health Laboratory and lead study author.

"We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some of these second infections, while rare, are presenting as more severe."

Waning immunity?

Vaccines work by triggering the body's natural immune response to a certain pathogen, arming it with antibodies it to fight off future waves of infection. But it is not at all clear how long COVID-19 antibodies last.

For some diseases, such as measles, infection confers lifelong immunity. For other pathogens, immunity may be fleeting at best.

The authors said the US patient could have been exposed to a very high dose of the virus the second time around, triggering a more acute reaction. Alternatively, it may have been a more virulent strain of the virus.

Another hypothesis is a mechanism known as antibody dependent enhancement — that is, when antibodies actually make subsequent infections worse, such as with dengue fever.

The researchers pointed out that reinfection of any kind remains rare, with only a handful of confirmed cases out of tens of millions of COVID-19 infections globally.

However, since many cases are asymptomatic and therefore unlikely to have tested positive initially, it may be impossible to know if a given COVID-19 case is the first or second infection.

In a linked comment to The Lancet paper, Akiko Iwasaka, a professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale University, said the findings could impact public health measures.

"As more cases of reinfection surface, the scientific community will have the opportunity to understand better the correlates of protection and how frequently natural infections with SARS-CoV-2 induce that level of immunity," she said.

"This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity," added Iwasaka, who was not involved in the study.

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First Published on Oct 13, 2020 10:35 am
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