COVID-19: Will herd immunity save us from coronavirus?

Three months have passed since the new coronavirus hijacked our lives. When will this pandemic end? In the absence of a cure, treatment protocol or even a vaccine, it is difficult to predict. There have been forecasts using models of other epidemics, but those may at best remain projections.

The SARS-CoV2, the virus that causes COVID-19, is like no other pathogen. Its genome has been sequenced early on, but many traits are still unknown. This is despite the tremendous scrutiny by scientists worldwide.

Several researchers have put forward the idea that immunity is perhaps the best route to return to normality. If the studies in China are any indication, this line of thinking is not without merit.

The data from China show that 80 per cent cases were mild, more like a bad case of flu, and 14 per cent of patients developed serious illness. The five per cent who died were elderly or people with compromised immunity. So it’s clear that a person’s immunity can ward off the virus attack.

What’s immunity? How does it work?

Immunity is the body’s natural resistance to fight off invading pathogens and their harmful effects. Innate immunity provides the first line of defence against infections. It is a generic rapid response, but it does not last long.

Adaptive immunity is a specific response to an invading pathogen. It is acquired following exposure to a foreign organism, and re-exposure to the same germs induces a more rapid immune reaction that eliminates the pathogen and prevents disease.

When politicians refer to herd immunity, they are referring to the adaptive immunity of a large population.

What’s herd immunity?

Herd immunity occurs when a group of people develop sufficient antibodies to become resistant to disease. It happens when a virus infects all the people in an area or community and makes them immune. The pathogen will no longer find weak hosts, and the outbreak will fizzle out on its own.

Epidemiologists say the more infectious the virus, the more people need to be immune to achieve herd immunity. And some people will die in the process.

“Herd immunity can only be reached when a precise proportion of a community becomes resistant to an infectious disease, Yonatan Grad, an epidemiologist at the Harvard T.H. Chan School of Public Health, told the National Geographic.

Herd immunity and coronavirus

The COVID-19 virus is new to the world. So it’s unlikely anyone is immune to it. Which is why letting it spread is not a good idea. Many people will fall ill critically, and some can die.

“You don’t rely on the very deadly infectious agent to create an immune population,” Akiko Iwasaki, a virologist at the Yale School of Medicine, told The Atlantic.

Using research models of measles, scientists say that with the coronavirus herd immunity can be achieved only when around 60 per cent of the population becomes immune to COVID-19. That's a huge cost.

Britain, the Netherlands and herd immunity

Britain was swift so subscribe to the herd immunity option to fight the coronavirus. That was after Patrick Vallance, chief science adviser to the UK government, told Sky News that the country needed to “build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission.”

It had resonance in the Netherlands too. Prime Minister Mark Rutte said: “We can slow down the spread of the virus while at the same time building group immunity in a controlled way. It can take months or even longer to build group immunity, and during that time we need to shield people at greater risk as much as possible.”

Why Britain dropped herd immunity?

Britain’s initial strategy was to allow the virus to pass through the country’s population so that they acquire herd immunity. In that event, only those who suffer acute symptoms will have to be treated, and the state-run National Health Service will not be overwhelmed.

The idea was quickly abandoned after a new analysis by immunologists at Imperial College London and the London School of Hygiene and Tropical Medicine of the impact of the coronavirus in Italy showed that around 30 per cent of hospitalised patients will require intensive care treatment. If those numbers are replicated in Britain, NHS would collapse.

A better route to herd immunity

Vaccines offer a better way of obtaining herd immunity since the antibodies are developed through vaccination rather than infection. But there’s no viable vaccine. Around 35 companies and research institutions are racing to develop a vaccine, but the one developed by Moderna is the first to reach a clinical trial. Even if it clears all the hurdles, it would take at least 18 months to be ready.

Is immunity the way out?

Immunity certainly holds the key to a return to normality. The virus is expected to stay around, and we would have become immune to it, epidemiologists say. In some cases, some may fall ill and recover soon. There would be fatalities too, the frail and the infirm with weak immune systems.

Bloomberg Opinion columnists Joe Nocera and Max Nisen call for antibody testing so that people with immunity can resume normal activities. Serology tests are easy to administer and easy scale, they write, arguing that communities can be easily tested.

Nocera and Nisen say, “lower-risk, uninfected people who don’t work in high-contact environments might be able to join the immune population as long as they took proper precautions.”

There are several potential drawbacks. “It takes the body some time to develop detectable antibodies — sometimes as much as a week or more after infection — so serology tests are not especially useful as a diagnostic tool,” they say.

So in the absence of a cure, a vaccine and a swift reliable antibody test (PCR tests — reverse transcription-polymerase chain reaction — are the only option now), we can’t say for sure when we all will be immune, or when we can resume normal activity.

Why India, Egypt and Africa have fewer cases?

Confirmed cases are not a reliable metric. Because it is relative to the number of people in a country. In India, a country of 1.3 billion people, around 1,600 cases doesn’t make sense. Especially given the virus’ ability to transmit rapidly.

There’s a school of thought that believes that tough hardy people are generally immune to some diseases. That could include the coronavirus, they argue, attributing fewer cases in India, Egypt and the rest of Africa to the people’s innate immunity. But in the case of coronavirus, it has to be adaptive immunity — one that’s acquired through infection.

The most likely explanation is the low rate of testing in these countries.

With a population of 1.5 billion people, China’s some 80,000 cases look like a rounding error, Bloomberg Opinion’s Faye Flam writes quoting Nigam Shah, an assistant professor of biomedical statistics at Stanford. “And India’s claim...probably reflects a severe lack of tests — not that the disease there is still so rare. The positive tests say little about how many people are dying or will die since most cases are mild,” Flam adds.

What about the risk of reinfections?

There are reports of reinfections in people who have recovered from COVID-19. Researchers are not certain whether these are reinfections or whether these are people continuing to shed the virus after their recovery.

Rapid reinfection is an outside possibility, Jessie Abbate, an infectious disease expert at the Research Institute for Development in France, says. “If people were able to get sick again really quickly, we wouldn’t see the rapid decline in case numbers that is happening in certain parts of the world. And it would go against almost every other virus that we’ve known about,” she adds.

When will COVID-19 end?

When can our lives return to normal? Nobody is willing to put a specific timeframe. Several months, scientists say.

“We don’t know enough about the science of this virus, it hasn’t been in our population for long enough for us to know what it does in immunological terms,” Dr Margaret Harris, WHO spokeswoman, says.

“Every virus functions differently in your body and stimulates a different immunological profile. We can talk theories, but at the moment we are really facing a situation where we have got to look at action.”

So let’s take action. Social distancing the best option now. Stay at home. Wash our hands. And wait for the virus to blow over.