MANILA — Philippines will not achieve herd immunity against the coronavirus disease (COVID-19) without a vaccine, an expert said Thursday.

Herd immunity means a large percentage of a population has become immune to an infection like coronavirus disease.

“I don’t think so….A threshold of the general population should be immune to the disease. As of now we only have a few who have recovered and our population is 100 million,” vaccine trialist Dr. May Montellano told media during a webinar organized by the Philippine Medical Association.

As of Wednesday, the Philippines has had 294,591 total COVID-19 cases.

Montellano, a former president of the Philippine Foundation for Vaccination, explained that herd immunity can be achieved either through an outbreak or by mass vaccination of the population. And the latter is safer and more effective.

The Agence France-Presse reported on Thursday that a study estimates that 66% of the population of Brazil’s city of Manaus already had antibodies against the COVID-19 disease. This meant that the disease might not effectively spread anymore in the area because enough members of the population are already immune to it.

• Amazon city of Manaus may have reached 'herd immunity': study

But the price of herd immunity is high. The city already has 2,462 COVID-related deaths out of its 2.2 million population and when the outbreak peaked, mass graves had to be dug.

Experts said herd immunity through natural infection should not be considered as a strategy.

“It's a sign that a government failed to control an outbreak and is paying for that in lives lost," Florian Krammer, professor of microbiology at the Icahn School of Medicine at Mount Sinai Hospital in New York, was quoted saying in the Agence France-Presse report.

Herd immunity via natural infection made headlines before when Sweden decided to impose relaxed quarantine restrictions. A BBC report in July said that while Sweden did not claim to target herd immunity, officials said that by keeping their society open, people will develop a resistance to COVID-19. (Reference: https://www.bbc.com/news/world-europe-53498133)

But as the BBC article pointed out, only 6% of the population has antibodies against the disease and the country has one of the highest death rates. With a population of about 10 million, COVID-19 cases in Sweden has reached 89,436 while deaths were at 5,870, based on the World Health Organization’s dashboard as of Thursday.

Montellano said herd immunity through natural infection can also be dangerous in the long run.

“The herd immunity can be diluted every year if there is no vaccination to prevent the disease. Because over time even through natural infection, immunity can wane. And so therefore it will reduce your protection against the disease,” she said.

“We are not sure if (natural) immunity is really protective,” Montellano said, adding that vaccines are better because they go through tests to determine effectivity.

She added that there will always be a portion of the population who will be vulnerable to the disease since babies are born yearly and are not immune to the disease.

Montellano also cautioned that once herd immunity falls, “there will be many people who will be susceptible and outbreaks will occur.”

Experts have said that the first COVID-19 vaccines won’t be available publicly in the Philippines until next year. Currently, there are several vaccine manufacturers applying to run clinical trials in the country.