PH experts advise against mixing COVID-19 shots

MANILA, Philippines — Limited global supply and logistical challenges increase the likelihood of different brands of the COVID-19 vaccine becoming available within the short period between the first and second shots.

But Filipino experts on infectious diseases advised against administering varying brands of the vaccine on a person—an important consideration for the government as it aims for a rollout and supply allocation this month.

Vaccines are made with “different platforms,” each with its unique makeup, said Dr. Rontgene Solante, chief of the Adult Infectious Diseases and Tropical Medicine unit of San Lazaro Hospital.

“In the realm of vaccination, we don’t mix vaccines with different platforms,” Solante said in a phone interview on Wednesday.

ALMOST FOR REAL Health Secretary Francisco Duque “reacts” while getting a COVID-19 shot during a demonstration at Pedro P. Cruz Elementary School in Mandaluyong City on Friday. —MARIANNE BERMUDEZ

Different pathways

Dr. Lulu Bravo, executive director of the Philippine Foundation for Vaccination, said no COVID-19 clinical trial had ever tested two different brands on a single participant.

To see a vaccine’s effectiveness, a person must complete two doses of the same brand, Bravo said in a separate phone interview. “It takes at least a year to see its effectiveness,” she said.

Secretary Carlito Galvez Jr., chief implementer of the government’s vaccine program, said 117,000 doses from Pfizer-BioNTech were expected in February, and from 5.5 to 9.2 million doses from Oxford AstraZeneca during the first quarter.

Pfizer’s vaccine is an mRNA (messenger RNA) vaccine, which, according to the US Centers for Disease Control and Prevention, is a new approach to trigger an immune response.

Oxford AstraZeneca’s vaccine is a viral vector vaccine, which uses the harmless chimpanzee common cold virus.

“We don’t know how the interaction [of two brands] will be. One could produce antibodies, the other could take a different pathway,” Solante said.

Of the available vaccines, Pfizer’s is closely similar to Moderna’s, which is also an mRna vaccine, he said, adding: “In the United States, they always allocate the second dose for the [same] patient.”

Vaccine brands also have varying intervals between the first and second shots—Pfizer’s is 21 days, Moderna 28 days, and AstraZeneca one to three months—and therefore have different logistics and storage requirements.

Follow-up mechanism

In order to avoid mixing brands, the government must finalize the master list of all willing health workers—the priority recipients—and store an exact amount of the same vaccine for them until their second shot, Solante said.

He raised the need for a strong follow-up mechanism to ensure that the second shot is administered even after several weeks.

Long intervals have a “disadvantage,” Solante said. “Some people might already feel complacent [after the first dose].”