Targeting 95% herd immunity against coronavirus disease 2019 (COVID-19) is unachievable in light of the highly transmissible Delta variant of the coronavirus, according to Tikki E. Pangestu, an infectious disease expert and visiting professor at the NUS Yong Loo Lin School of Medicine in Singapore.
With the Delta variant now dominant in most countries, the target should instead be disease immunity, or the prevention of severe disease and deaths from the virus, he said at a Sept. 8 event organized by pharmaceutical company MSD.
“With the Delta variant having a multiplication value close to 8, getting a herd immunity of 95% is a myth,” Mr. Pangestu said. “For me, the target of COVID-19 vaccines is not to stop the spread of infection, but to stop severe disease [and] prevent people from ending up on a ventilator and dying.”
The basic reproductive number (R0 or R-naught) for the Delta variant ranges from 3.2 to 8, according to the Journal of Travel Medicine. To compare, the R0 of the influenza virus is between 0.9 and 2.1.
R0 is the average number of people that one infectious individual is likely to infect in a population without any immunity or any interventions.
Mr. Pangestu also cautioned against comparing countries like the Philippines and Indonesia with countries like Singapore, which has already fully vaccinated close to 80% of its population.
The comparison is unrealistic, he said. “The logistical challenges in countries like the Philippines and Indonesia are more challenging than small island [nations] like Singapore.”
Ending the pandemic and securing global recovery, according to the World Health Organization, depends on vaccine equity.
“Equity is a problem,” said Dr. Lulu C. Bravo, emeritus professor of pediatric infectious and tropical diseases at the University of the Philippines Manila. “We have made recommendations that ensure that those in high density areas are given priority.”
The country, she added, has the infrastructure to deliver COVID-19 vaccines to those who need them the most.
“We have midwives and LGUs [local government units]. We have a home delivery system that can bring vaccines to far-flung areas. It’s the supply we have to be concerned about,” Dr. Bravo said, adding that poor nations should be vaccinated before rich ones start considering booster shots.
A concurrent concern is vaccine hesitancy, or the reluctance or refusal to vaccinate despite the availability of vaccine services.
“Vaccine hesitancy is a spectrum, a broad continuum of opinion,” said Mr. Pangestu, adding that efforts should focus on the 70% who sit in the middle of this spectrum — those who will ultimately refuse, delay, or eventually accept vaccination.
If there’s a silver lining in the pandemic, it’s the unprecedented solidarity of different stakeholders coming together for collective action, said Lynn D’Silva Cinelli, MSD’s executive director for manufacturing operations.
“That’s what a crisis does. It gives you focus,” she said. MSD partnered with Johson & Johnson to expand the manufacturing capacity of its COVID-19 vaccine. — Patricia B. Mirasol
