COVID-19-Helminth Syndemic May Curb Vaccine Efficacy in Tropical Areas

By Marilynn Larkin

June 14, 2021

NEW YORK (Reuters Health) - Researchers and clinicians in Latin America suggest a potential synergistic epidemic, or syndemic, between helminth infection and COVID-19 and urge research on strategies to decrease helminth co-infection before implementation of a COVID-19-vaccine initiative.

"The effects of these pathogens on COVID-19 vaccines efficacy must be considered during the current deployment of the mass use of COVID-19 vaccines in these endemic regions, ideally before," Dr. Alfonso Rodriguez-Morales, associate editor of Travel Medicine and Infectious Disease, and colleagues write in an editorial in that journal.

"The possible implications of the immune-regulatory role of helminth intestinal infections in humans co-infected by SARS-CoV-2 and its effect on the viral disease outcome and COVID-19 vaccines efficacy must be considered carefully (before) using them in endemic helminth areas, in terms of more studies to understand this relationship," they add.

Other areas of necessary research, they note, include massive deworming, "boosts to induce a T-cell response," immune-modulating therapies and use of adjuvants.

Further, they suggest, studies of melatonin as "a potential complement or therapeutic alternative to combat viral, bacterial, and parasitic infections" are needed so the hormone can be considered for prophylactic use, monotherapy or in combination with other drugs.

"On the other hand," they say, "the several strategies that have been proposed to diminish helminths' impact over viral vaccination are not feasible in Venezuela due to its current economic collapse. The situation in this country is incredibly distressing due to the collapse of the health systems, the scarcity of medicines and care policies for seniors and the impoverished."

These and other factors could lead to high COVID-19 morbidity and mortality, and impact the vaccines' effects on the immune system, they conclude.

Dr. Keith Armitage, medical director of the Roe Green Center for Travel Medicine and Global Health at University Hospitals Cleveland Medical Center, in Ohio, told Reuters Health by email, "The authors speculate how immune activation due to chronic helminthic infections might impact the response to SARS-CoV-2 infection and the response to vaccination."

"Their hypothesis-generating ideas could be explored with large clinical studies looking at the clinical and immunologic response to infection and vaccination in areas with a heavy background of helminthic infection, but this may be challenging in resource limited countries," he said.

"If helminthic infection was shown to complicate COVID-19 or vaccination, a helminth mitigation strategy could be part of an approach in these areas," he suggested.

"The authors speculate about the immune-modulating effect of melatonin," he added. "As is the case with so many putative interventions in COVID-19, this can only be adjudicated by well-designed trials before there would be high-quality evidence to recommend for or against use of melatonin."

Dr. Daniel Parker, assistant professor in the Program in Public Health at the University of California, Irvine, told Reuters Health, "As COVID-19 makes its way through (tropical and subtropical) parts of the world, there will definitely be co-infections with both SARS-CoV-2 and helminths."

"Co-infections can lead to complicated disease outcomes," he said by email. Helminths are macroparasites, and the immune system can't deal with them the way it deals with microparasites - i.e., through ingestion by phagocytic cells, he explained.

"What this means for disease outcomes when helminth-infected persons are also infected by SARS-CoV-2, or what this means with regard to the normally protective benefits of vaccination against SARS-CoV-2, is still an open question," he said. "As such, I'd say that the authors' hypotheses are valid (and) warrant further research and careful consideration."

Like Dr. Armitage, he suggested, "One option would be to treat with anti-helminths prior to vaccination. We need to cautiously monitor the situation to see if helminth-infected folks have different vaccine outcomes."

"We have good medications for treating helminth infections, but we desperately need new ones," he added. "Currently, there is only one class of widely used anti-helminth medication, and the use of monotherapies can drive the evolution of drug resistance. We need new types of anti-helminth medications so that we can use combination therapies."

Dr. Rodriguez and co-corresponding author Dr. Leonor Chacin-Bonilla of Zulia University in Maracaibo, Venezuela, did not respond to requests for a comment.

SOURCE: Travel Medicine and Infectious Disease, online May 20, 2021.