The chief scientist at the World Health Organisation estimates that about 50% to 60% of the population will need to be immune to the coronavirus for there to be any protective “herd immunity” effect.

Herd immunity is usually achieved through vaccination and occurs when most of a population is immune to a disease, blocking its continued spread.

During a social media event on Friday, Dr. Soumya Swaminathan said that studies done from some countries hit hard by Covid-19 show that about 5% to 10% of people now have antibodies, though in some countries, it has been as high as 20%.

She says: “As there are waves of this infection going through countries, people are going to develop antibodies and those people will hopefully be immune for sometime so they will also act as barriers and brakes to the spread.” Other experts have estimated that as much as 70% to 80% of the population need to have antibodies before there is any herd immunity effect.

In the pandemic’s earlier stages, countries including Britain proposed achieving herd immunity as an outbreak response strategy. But Swaminathan pointed out that achieving this effect with a vaccine is much safer than letting the virus rip through the population.

She says that to achieve herd immunity through natural infection, you need to have several waves and you will see the morbidity and mortality that we see now.

As work on the vaccine progresses, Dr Swaminathan said, the WHO is keen to avoid a situation like in 2009, when rich countries cornered the bulk of the vaccine doses after the H1N1 pandemic. “We are doing everything possible to avoid that and to ensure an affordable and equitable distribution of vaccines,” she said.

Meanwhile, Dr Anthony Fauci,one of the world’s top immunology experts and a Covid adviser to the Donald Trump administration,said Wednesday the novel coronavirus pandemic is a “perfect storm” whose end is “nowhere in sight”.   

Addressing a webinar organised by the TB Alliance, a US-based non-profit dedicated to research on tuberculosis drugs, Fauci described Covid-19 as the “worst nightmare” of an infectious disease expert or a public health professional.

“We are not at the end of the game, I am not even sure we are halfway through. We are not winning the game, not leading. With 600,000 deaths, it is threatening to overtake TB. It is a perfect storm,” he said at the “Fighting Pandemics | 2020 and Beyond” webinar.

“This virus has everything — it is a new virus, it jumps species, has a respiratory base, is spectacularly effective in spreading from human to human, is deadly to the elderly and people with comorbidities. We are living through a historic pandemic situation with no end in sight,” added Fauci, who serves as director of the US government’s National Institute of Allergy and Infectious Diseases.

He said the disease may be brought under control this year or 2021, but the virus is unlikely to disappear or be eliminated.

Models suggest diseases like HIV, TB and malaria could all go up due to the challenge the health systems are facing… We are extremely worried about the effect of the pandemic in low- and middle-income countries where measures such as lockdowns have caused loss of livelihood and estimates suggest poverty, undernutrition all may go up this year and there will be a setback in the SDG (UN’s sustainable development goals),” she said.Answering a question from The Wall Street Journal writer Betsy McKay, who was moderating the session, Fauci expressed hope that, “this year or next year”, the world will be in a position to control the pandemic. However, he said there is little chance of the virus being eradicated, or disappearing on its own like the SARS pathogen — also a coronavirus — responsible for the 2002-03 outbreak. 

“With a vaccine, public health measures and herd immunity, there may be very good control, although it is unlikely we can bring it down to the level of a common cold or flu,” he added.

“I have never seen an infection where you have such a broad range. Twenty to 49 per cent of people have no symptoms, some are mildly ill for a fortnight and then have post-viral syndrome, still others need hospitalisation, oxygen support, ICU care, and even die,” he said.

“That is why I don’t see it coming down to a level where everybody just escapes with a sniffle as happens with common flu.”

Even though there are several vaccine candidates in various phases of clinical trials, with some like the one developed by the Jenner Institute at Oxford University in phase III, there are better chances of a treatment coming up sooner than a vaccine, Dr Fauci said.