Philippines under scrutiny over launch of unconfirmed African swine fever vaccine

The Philippines has come under global scrutiny for the controlled introduction of an unconfirmed African swine fever (ASF) vaccine originating from Vietnam, raising doubts among experts about its safety and effectiveness.

ASF is a highly contagious viral disease that affects domestic pigs and wild boars. According to the World Organization for Animal Health (WOAH), the mortality rate of this disease can reach 100 percent.

There is no international vaccine against the virus, which has led to huge losses in the pig population due to a sharp increase in cases from 2022.

“There is a lot of concern,” said Ramon Clarete, an economics professor at the University of the Philippines Diliman who specializes in agricultural productivity. “We really have to be careful with this (vaccine) because the hog industry is a very important industry in agriculture.”

The concerns stem from a perceived lack of transparency from Vietnam regarding trial data and the nature of the ASF vaccine, which consists of a live virus that has been weakened by removing important parts of its genes. This type, called a live attenuated vaccine, could still pose a serious risk of mutating and reverting to its viral form.

“The risk with a live attenuated vaccine is that it may still have a bit of virulence that could cause disease or some type of discomfort or illness,” said Baptiste Dungu, a professor at the University of Kinshasa in the Democratic Republic of Congo and a vaccinologist with more than 30 years of experience in veterinary vaccine research, production and commercialization.

A study published in the journal Nature tested the virus strain in ten pigs and found that while it did not regain its virulence, a variant of the virus emerged in one pig that eventually spread to all ten pigs. The variant appeared to be slightly more replicative and had an increased risk of “shedding,” the study said.

“Shedding is when the virus is shed from a vaccinated animal and spreads to another animal,” Dungu explained.

“This phenomenon did not occur in any previous studies, but is important because it can also happen in the field during intensive use,” the authors wrote in the paper.

The Philippine Food and Drug Administration (FDA) said it carefully analyzed field trial data before granting the vaccine a Certificate of Monitored Release Product Registration (CPR MR), which allows its controlled use in the country.

“The CPR MR is issued by the FDA for new drugs and vaccines that have successfully met rigorous standards of safety, effectiveness, and quality required for approval,” the agency told SciDev.Net in a statement.

The vaccine, called the AVAC ASF LIVE vaccine, was developed by AVAC Vietnam JSC and imported to the Philippines by KPP Powers Commodities Inc. It is a derivative of a strain of the virus called ASFV-G-∆MGF, or ∆MGF for short.

However, on October 27, 2022, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) issued a public notice withdrawing ∆MGF from the regulatory exemptions for select agents because it “has evaluated new information and determined that it has the potential to pose a serious health risk to animals or animal products.”

“It was also determined that the virus strain is not safe for use in pigs because its genome is unstable, which could potentially lead to virulence reversal,” the notice warned.

As the basis for its decision, APHIS cited two scientific journal articles published by the Harbin Veterinary Research Institute in China, which stated that studies “detected instability within segments of the MGF genome.”

In December 2023, WOAH issued a warning about “substandard vaccine use” after the announcement of export agreements between vaccine manufacturer AVAC Vietnam JSC and Southeast Asian countries, including the Philippines. The warning urges authorities to use only high-quality vaccines with proven safety and effectiveness.

Despite those concerns, a controlled rollout of the vaccine will continue next month, with 150,000 doses being distributed to hog farms on a voluntary basis. The campaign will begin Sept. 2 in Lobo, Batangas, the “ground zero” of ASF outbreaks, according to Agriculture Deputy Secretary and spokesman Arnel de Mesa.

Last month, Agriculture Secretary Francisco Tiu Laurel told state television PTV that “the Vietnam vaccine really works.”

The Department of Agriculture did not respond to SciDev.Net’s request for additional information on the field trials.

The FDA said field testing has been underway in the Philippines for nearly two years and has determined the vaccine is 100 percent effective with no side effects. However, no data from the testing has been made public.

When asked for field trial documents, the FDA said they follow strict confidentiality protocols and that “direct access to them is not permitted.”

Former Undersecretary of State for Agriculture Jose Reaño questioned the credibility of the trials, explaining that he had not seen field trial documents.

“If the results are really positive, they should be proud and share the data with the public,” Reaño told SciDev.Net, adding that the government should not rely on the vaccine as its main form of intervention.

Last year, the trials came under scrutiny at a Senate hearing, with Senator Cynthia Villar questioning KPP Powers Commodities Inc. about its involvement in the trials. The senator noted a conflict of interest and said the Agriculture Department should independently conduct the field trials.

SciDev.Net attempted to contact KPP Powers several times but did not receive a response before publication.

“I am in favor of introducing this (vaccine) if experts say it is safe,” Clarete said.

However, he added that the FDA should be more transparent about clinical trials.

The Philippines is one of 19 Asian countries hit by ASF since 2019, according to the Food and Agriculture Organization of the United Nations. The disease has since spread to 74 of 82 provinces and reduced the country’s pig population from 12.7 million in 2019 to 9.9 million in 2023.

According to Nicanor Briones, AGAP party representative and chairman of the Philippine Pork Producers Federation, the hog industry’s losses amounted to at least PHP 200 billion, or about US$3.5 billion, in July 2023.