Scientists believe that coronavirus recovery is likely to leave a person with some immunity, but it is not clear how strong it is or how long it will last. Re-immunity is the idea that a disease ceases to spread once a population becomes immune – and is appealing because, in theory, it can provide some protection for those who are not sick.
If more than half of the people in Mumbai’s mumps contracted coronavirus, would they be able to approach herd immunity – without vaccination?
One expert thought so.
“Mumbai slugs may have acquired breeding immunity,” said Jayaprakash Muliyil, chairman of the Scientific Advisory Committee of India’s National Institute of Epidemiology, according to a Bloomberg report. “If people in Mumbai want a safe place to prevent infection, they would probably have to go there.”
But others have been more cautious. David Dowdy, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, said it was possible that the researchers used a test that made false positions.
And Om Shrivastav, an expert expert in Mumbai, warned that, less than eight months after the virus’s existence in society, it was too early to make “decisive, decisive statements.”
The risk of a high death toll is exactly why the health authorities of India de land does not target herd immunity. “Re-immunity can be achieved through immunization – but that is in the future,” health official Rajesh Bhushan told reporters last month.
What is herd immunity?
Herd immunity works like this: Suppose each infected person infects three more people. If two of those three people are immune, then the virus is only able to make one person sick. This means that fewer people are infected by the disease – and over time, even people who are not immune are protected because they are less likely to be exposed to the disease. virus.
The level of immunity required in a population depends on the disease. Scientists do not yet know what proportion of a population must be immune to achieve herd immunity to the new coronavirus.
Building the level of immunity in a population can happen in two ways. People can become immune by getting vaccinated, or they get caught develop the virus and natural immunity by recovering from it.
And that’s where things get controversial.
Most other countries – including India – have taken a different approach. “Re-immunity in a country with the size of India’s population can not be a strategic choice. It can only be an outcome and that too, at a very high cost,” said the health official, Bhushan.
As Dowdy puts it: “We were able to develop a rapid immunity for a coronavirus population by exposing just one person in the population to the disease … it’s just that millions and millions of people will die in the process.”
Can we build natural immunity?
The science surrounding immunity for Covid-19 is still evolving.
The fact that antibody levels decrease over time does not necessarily mean that immunity does not last, Dowdy says. In other viruses, antibody levels drop over time as well, but the immune response is still able to recover when a person is re-exposed to the virus.
According to Dowdy, our immunity to other coronaviruses has lasted for several years, instead of being lifelong. “If that’s a manual, then that’s what we can expect from this new coronavirus,” he said. “But it’s bad to say. We have no data on this particular virus.”
But for now, Tanoto says we do not know how much – if at all – these T cells help fight Covid.
In fact, once there is herd immunity – whether natural or through faxes – it will probably not be the implicit shield that some people might imagine.
Tanoto’s co-author Nina Le Bert, a senior research fellow at Duke-NUS Medical School in Singapore, points out that it is rare to have full immunity to infection. Instead, immunity often means that a person’s body can react quickly enough to the virus so that it does not get a foothold – and does not develop enough to infect other people.
“That would be good enough, but that doesn’t mean you don’t get infected,” Le Bert said.
What does this mean for herd immunity?
Even if certain areas develop herd immunity, it may not last.
The virus could mutate, meaning people who previously had immunity would no longer be immune to the new version of the virus, as a person’s immunity to the virus might not last long, according to Kleczkowski, of the University of Strathclyde.
“Even if at some point we reach immunity to herds, we can lose it again,” he said. “I do not think it is a silver bullet.”
Dowdy says herd immunity is “not a magic number” to solve coronavirus.
“It does not mean that the disease will go away. It does mean that if you gave it 1000 years, it would go away.”
And he notes that how long herd immunity lasts – whether it is in a slum or an entire country – depends in part on how much movement there is in and out of this population. When people enter the area without immunity, it lowers the overall level of immunity of the population. If enough people come in, it could mean that there are enough people without immunity for the virus to spread again.
In a Mumbai slum, for example, people are likely to come and go, which can affect how long herd immunity – if any – lasts. Utture Shankar, the president of the Maharashtra Medical Council, said that people outside slum areas depended on those living in slums for services such as gardening, cleaning and driving, so would be exposed outside their residential area.
When it comes to coronavirus, vaccines are the key to herd immunity – and controlling the virus, Dowdy says.
“I think this is a disease that will be with us for a while,” he said. “But I do not think it will be a disease that causes the same level of death and suffering as it is now.”
CNN’s Esha Mitra contributed to this story from New Delhi.
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