MANILA - People given China's Sinovac for primary COVID vaccine could get more antibodies with a heterologous booster shot, an expert explained Tuesday, as the Philippines continues to beef up its vaccination drive.

"Yung nakatanggap ng Astra, Janssen and Pfizer vaccine mas mataas yung antibody level nila kumpara doon sa nakatanggap ng Sinovac as a 3rd dose," said Dr. Rontgene Solante, a member of the vaccine expert panel and head of adult infectious disease at San Lazaro Hospital.

Citing a study by Sue Ann Costa Clemens et al. published in medical journal The Lancet, Solante said that for those whose primary series was CoronaVac by China's Sinovac, the antibody levels produced by heterologous vaccine booster shots or other brands such as Pfizer, AstraZeneca and Janssen, antibody response was superior to homologous booster or a third dose of Coronavac.

"All of these elicited a substantial rise in IgG (antibody) level. All of the heterologous regimes had spike antibody response at day 28 that were superior to homologous booster," said Solante.

Meanwhile, an Astrazeneca beta variant-specific vaccine protects vs other variants, said Solante, citing a study published by AstraZeneca on the phase II/III of its trial.

According to the study, the beta variant-specific vaccine, when given as a third dose for those who received AstraZeneca or an mRNA vaccine like Pfizer or Moderna, also protects against other variants of concern.

"They got positive results from preliminary analysis of an ongoing safety and immunogenicity trial that this vaccine if given as 3rd booster dose can increase the immune response to Beta, Delta, Alpha and Gamma," Solante said.

"The main point here is that with variant-specific vaccine it can be protective against that variant and have cross-protection against other variants of concern," Solante added.

T-cells recognize omicron variant

T-cells or the soldiers of the body's immune response still recognize the omicron variant even if it gets past the antibodies, according to Dr. Mario Jiz, member of the country's vaccine expert panel and head of the Immunology Department and Research and Innovation Office at the Research Institute for Tropical Medicine (RITM).

• Why antibodies aren't the only defense against Omicron

"Even though you get only 2 doses of vaccine, regardless of what vaccine you get, your t-cells can still recognize the omicron variant," he said.

"It will still mount a protective response against the omicron variant
kaya ang ating vaccinated na mga kababayan (those vaccinated)...once its inside either body the t-cells will start killing these viruses kaya mild symptoms na lang nakukuha nila (that's why the only get mild symptoms)."

Jiz urged the public to get vaccinated to provide protection for the vulnerable population.

"By vaccinating, you are protecting your grandparents, your parents and elderly, family members from the infection," he said. "Yung benefit po ng pagbabakuna kumpara sa risks or side effects ay napakalaki po."

(The benefit of vaccination compared with risks or side effects is larger.)

All vaccines work against hospitalization and severe disease, Solante added.

"We also lessen the transmission, we lessen the emergence of mutations in the future," he said.

COVID-19 vaccines available in the Philippines are expected to give protection, especially from severe disease, for a "minimum of 6 months to one year," Jiz emphasized.

"In terms of biological efficacy, safe to say, minimum of 6 months to 1 year may protection tayo especially from severe disease. I think more than 1 year pa nga siguro ang protection natin from severe disease," he told reporters.

(In terms of biological efficacy, safe to say, we have a minimum of 6 months to 1 year protection, especially from severe disease. I think more than 1 year protection from severe disease.)

"I'm putting it on the context of yung mga pinsan ni COVID (other coronaviruses). We also have other coronaviruses that are circulating, di lang kasing severe ni (they're not just as severe as) COVID."

He added that after immunity wanes following a year, "that maybe a good time for a variant-specific vaccine."

"Wag naman sana every year pero (Let's hope we won't do it every year but) every time there's a concern mutation or variant that comes in we may have to re-immunize our population," he said.

The Philippines has so far fully vaccinated 55.6 million individuals, while 59 million have received an initial dose and 5.13 million booster shots have been administered, according to Department of Health data.

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