Coronavirus reinfection What it means for COVID vaccine development, herd immunity

New information and discoveries about the novel coronavirus are coming out almost every day even as scientists and health researchers are working at unprecedented speed to find a safe and effective vaccine against this baffling virus. Researchers have demonstrated how the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreads, how long it takes for infected people to develop symptoms, how long it can last on surfaces, etc. However, there’s still a lot to be determined, including why the virus is so infectious, how it can be treated effectively, how well antibodies can protect against reinfection, whether people who get reinfected with COVID-19 can transmit the virus and more.

Several cases of people becoming reinfected with COVID-19 have come to light after researchers in Hong Kong reported what appears to be the first confirmed case of reinfection in a 33-year-old man. Cases of reinfection have raised concerns about the durability of immune protection from the SARS-CoV-2 virus, and whether it will impact vaccine development, etc. Researchers said while reinfection is rare, it is possible for humans to become infected with the SARS-CoV-2 virus multiple times, indicating that people should be cautious.

How worried should you be about COVID-19 reinfection?

For infectious disease experts, reinfections are normal and should be expected even as they caution against drawing broad conclusions. Researchers said people who get COVID-19 develop healthy immune response filled with both antibodies and T cells – just like what happens after other viral infections. But the body’s immune response gradually declines over months (within around three months) after the infection has been cleared, making people vulnerable again. Antibodies are molecules that can block pathogens from infecting cells, whereas T cells are a type of white blood cells that kill infected cells.

So, a person can’t necessarily be considered invulnerable to a reinfection. Yet, immunologists believe that the immune response generated after an initial infection should stave off serious illness even if it can’t prevent a second infection. That’s what happened to the 33-year-old Hong Kong man (the first known reinfection case), who was hospitalised again but remained asymptomatic, indicating that an initial immune response might protect the body against the disease. The virus samples from both of his infections suggested they are of different origin and are different strains. The researchers claimed that the viral material from the first infection differed from the second infection with respect to 24 nucleotides (building blocks of amino acids).

“The fact that somebody may get reinfected is not surprising,” Malik Peiris, a virologist at the University of Hong Kong, was quoted as saying by STAT last week.  “But the reinfection didn’t cause disease, so that’s the first point,’ Peiris said on the first reinfection.

Reports of COVID-19 reinfections have also been reported from the Netherlands, Belgium and the US. The Nevada case, which has been detailed in a new paper published on an online preprint server, was a counterexample to the Hong Kong case. Researchers said the 25-year-old man from Reno, Nevada, was reinfected with COVID-19 some 48 days after recovering from a relatively mild infection – he had a sore throat, cough, headache, nausea and diarrhoea. But this time (second infection), he became so ill that he had to be hospitalised with pneumonia. Researchers sequenced the RNA from both virus samples and found that man was infected with different strains of SARS-CoV-2 virus, which is a clear indication of reinfection. The study has not yet been reviewed by peers.

While infections and immune responses may vary widely in different people, researchers still don’t know how long immunity will last or why some people were reinfected with COVID-19.

Reinfection ‘may represent a rare event,’ the Nevada researchers wrote, adding the findings implied that initial exposure to the virus may not result in full immunity for everyone who has been infected by it.

“After one recovers from COVID-19, we still do not know how much immunity is built up, how long it may last, or how well antibodies play a role in protection against a reinfection,” Pandori said in a statement from the University of Nevada at Reno.

“This is a novel disease. We still have a steep learning curve ahead and lots of work to do, especially as inconvenient truths arise,” Pandori added.

Will reinfections affect herd immunity and vaccine development?

If we find a safe and effective vaccine against COVID-19, herd immunity is still possible because vaccines can be more protective than infection-acquired immunity, reported The Conversation. According to some epidemiologists, at least 70 per cent of a population needs to be immunised to achieve herd immunity.

“Caution needs to be exercised before jumping to conclusions with respect to reinfections. Herd immunity is not an option for any country. Even if happens, it will be at a huge cost with very high mortality rates. Any genetic mutations with the SARS-CoV-2 virus may impact herd immunity. Mutations may have the potential to affect the vaccine development,” Dr Satyanarayana, HOD & Consultant – Pulmonology, Lung Transplant Physician, Manipal Hospitals Old Airport Road, Bangalore, told Times Now Digital.

According to the Nevada researchers, the implication of reinfections is that a vaccine might not be able to provide 100 per cent protection, adding that is ‘an established understanding, with influenza regularly demonstrating the challenges of effective vaccine design. The researchers noted that one case doesn’t prove a widespread phenomenon.

Since the COVID-19 outbreak, there have been many SARS-CoV-2 mutations detected across the world. Perhaps, the SARS-CoV-2, like all other viruses, can mutate. So, it’s possible that several different vaccines would be required to combat multiple strains of the virus – like the way it’s done with the flu shot.

Do people who have Covid-19 a second time transmit the virus?

Unfortunately, both the studies – the Hong Kong case and the Nevado case – did not look at this question. So, it’s unclear at the moment whether people who get coronavirus disease a second time can transmit the infection. The same goes for asymptomatic carriers and scientists don’t know why this happens. As per the WHO, available data from contact tracing reported by countries suggests that asymptomatic people are much less likely to transmit the virus than those who develop symptoms.

“The most important question for reinfection, with the most serious implications for controlling the pandemic, is whether reinfected people can transmit the virus to others,” Columbia University virologist Angela Rasmussen wrote in Slate.

What are the measures that people can take to avoid reinfection with COVID-19?

According to Dr Satyanarayana, the best recourse to ward off the peak of pandemic and also reinfections is to follow the five commandments:

  • Practicing physical distancing
  • Avoiding crowded and closed space gatherings
  • Wearing masks at all times when outside
  • Meticulous hand hygiene
  • A successful vaccine with wholesome participation in vaccination when it comes to India.

This should apply to everyone, including patients who have recovered from COVID-19. 

The bottom line is, strictly adhering to guidelines and making healthier lifestyle choices is the best way to stay safe from this dreaded virus, which has so far resulted in more than at least 843,149 deaths worldwide, in the absence of a specific treatment or vaccine.



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