Singapore — The once touted ‘herd immunity’ against Covid-19 may never happen, scientists now say, given the new and more highly transmissible variants of the virus that have emerged.
There have also been breakthrough infections even for those who have received vaccines, which were previously thought would be the silver bullet against Covid.
Last year, when the pandemic began, many countries had looked to the concept of herd immunity as the goal for reopening economies and life going back to normal.
With new variants of the virus, especially the Delta variant, this goal seems to have moved out of reach, and countries have had to rethink their strategies moving forward.
The first herd immunity numbers floated in 2020 were 60 to 70 per cent, with even the World Health Organisation saying that with this number of people achieving immunity through vaccinations or previous infections, the number of people infected with the virus would decrease and eventually cease.
But now, with infections still in high numbers in areas with over 50 per cent vaccination rates such as the United States and the United Kingdom, this is no longer the reality.
In the UK last week, the director of the Oxford Vaccine Group, Andrew Pollard said that mainly because of the Delta variant, “herd immunity is not a possibility because it still infects vaccinated individuals.”
Bloomberg reports that according to the Infectious Diseases Society of America, due to the Delta variant, the threshold for herd immunity is now over 80 per cent, and may even be close to 90 per cent.
The director of the Vaccine Research Group at the Mayo Clinic, Greg Poland, is quoted by Bloomberg as saying that even with a 95 per cent vaccination rate, herd immunity will still not be achieved.
“It is a neck and neck race between the development of ever more highly transmissible variants which develop the capacity to evade immunity, and immunisation rates,” he said.
There are other experts who also believe that focusing on herd immunity in the first place was unrealistic, to begin with.
Harvard epidemiologist and expert in communicable disease dynamics William Hanage has called it “damaging” because “it presents people with an unrealistic vision of how the pandemic comes to a close and doesn’t account for the evolution of either the virus or the nature of disease in reinfections.”
Oxford’s Prof Pollard said that with even more variants likely to emerge, any country’s vaccine program should not be built around herd immunity.
This is why some countries, including Singapore, are now choosing to treat Covid-19 as endemic, meaning, like the flu, there will be infection breakouts from time to time, and yet, with enough people vaccinated, the illness people experience will be much milder.
British immunology professor Danny Altmann said the “more people on the globe effectively vaccinated, the fewer viral copies we’ll have on the planet, thus the less spread and fewer lungs in which for virus to mutate and spread the next wave of variants.”
/TISG
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