With drop in Covid cases, experts wonder if Chile has reached herd immunity

Santiago, Jul 28 (EFE).- Chile, a country where almost 80 percent of the population is completely vaccinated against Covid-19, over the last month has seen a drastic drop-off in cases and virus-linked intensive care unit admissions, a scenario that is leading experts to ask whether much-yearned-for herd immunity has been achieved.

After a serious second Covid wave that lasted from March to July and put Chile’s hospital system on the ropes, the pandemic has resurged to levels not seen since April 2020 but the country is partially recovering a “normal” rhythm after a long period of harsh restrictions.

“We have 46 percent fewer new cases on the national level compared with the last 14 days and four regions have registered a positivity rate of zero percent,” Health Minister Enrique Paris said.

Health authorities announced the lowest figure in the last 15 months for new cases on Tuesday, noting that 753 newly confirmed infections had been detected, a far cry from the more than 9,000 daily cases during the second wave, and at the same time they reported that the national positivity test rate has been below 3 percent for the past 10 days.

This improvement comes simultaneously with one of the world’s most successful immunization campaigns, with 79.2 percent of Chileans having been fully immunized, more than 86 percent having received at least one dose of the vaccine and 12 of the country’s 16 regions surpassing the 80 percent vaccination threshold.

The country, which in the past 24 hours registered 828 new Covid cases and 25 deaths, had taken more than five months after the start of mass immunization to stabilize the pandemic, with more than 1.6 million cases having been detected since the coronavirus hit the country and a death toll of 35,175.

The rise in new cases is due, among other factors, to the fact that the vaccine that is being most widely administered, China’s Sinovac vaccine, has somewhat lower efficacy in preventing infection than other vaccines, experts said.

This vaccine, one of six approved for distribution in Chile, is 65.3 percent effective in preventing serious illness and hospitalization due to Covid compared with the 95 percent efficacy of the Pfizer/BioNTech vaccine and 80 percent for AstraZeneca, which is also being used in Chile but to a lesser extent.

Nicolas Muena, a virologist with the Science and Life Foundation, told EFE that Chile “has reached a situation of herd immunity that protects against hospitalizations, serious cases and deaths, although it still does not ensure that transmissibility is halted.”

One of the risk factors, he said, is that there are still people who are susceptible to being infected – more than five million people who are outside the vaccination population, including children younger than 12 – as well as two to three million people who have been reluctant to get the jab, that is people who can get vaccinated but haven’t done so.

One must also take into account that the quantity of antibodies declines over time within vaccinated people, such that “it is recommended that a third dose be administered, something that the government is studying,” Muena added.

For Dr. Flavio Salazar, the assistant dean of research at the University of Chile, the country right now is in a “state of equilibrium” and has developed a level of protection “that has permitted infections to be reduced.”

However, he said, the concept of herd immunity, which means that the virus is no longer spreading, “is not black and white, but rather it’s a relative index and is subject to ongoing fluctuations,” especially with the new virus variants, which “prevent us from ruling out future outbreaks.”

“This indicator is not conceptually realistic, especially in a completely globalized world where just a small percentage of the population is vaccinated,” added Salazar, who heads the Millennium Immunology and Immunotherapy Institute (IMII).

Added to this is the uncertainty currently swirling around the Delta variant, which the World Health Organization says is the most transmissible variant yet to emerge and which so far has infected at least 30 people in Chile, according to what the general secretary of the Chilean Medical College (Colmed), Jose Miguel Bernucci, told EFE.

“Despite the fact that we’ve had excellent numbers and we’re seeing the vaccines’ effects in the population, we can’t let our guard down because we could lose everything we’ve gained,” he said.

EFE