Sinovac vaccine's efficacy vs Delta 'wanes' after 6 months — expert

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Metro Manila (CNN Philippines, August 30) – The guidelines on giving booster shots to healthcare workers and the elderly who received Sinovac COVID-19 vaccine should be reviewed after recent studies showed its "waning" efficacy against the Delta variant, a vaccine expert said on Monday.

Infectious disease specialist Dr. Rontgene Solante shared a recent study in Thailand which showed that while the efficacy of Sinovac vaccine against the original coronavirus strain is 98.33%, it went down to 75% for Alpha variant and 70% for Beta variant.

The vaccine's level of protection against Delta variant dropped to 48.33% six months after receiving the second dose. This is lower than the 93.33% efficacy of neutralizing antibodies that protect a person from the virus following a recent COVID-19 infection.

"Meron kang natural infection antibody more effective against the Delta variant…That concerns us kasi kung ganun ang nangyayari in Sinovac, why is it not able to produce antibodies enough to protect us?" he said.

[Translation: There is a natural infection antibody more effective against the Delta variant…That concerns us because if that is happening with Sinovac, why is it not able to produce enough antibodies to protect us?]

"Is there something wrong with the preparation? Is there something wrong in the way the vaccine stimulates our immune response?" he added.

Solante said this means those who have yet to receive their Sinovac shots can still benefit from the protection it offers against severe disease, but a booster shot may be needed six months after receiving the vaccine.

"Those unvaccinated now, Sinovac can still protect you against variants of concern. The question now is how about those vaccinated six months ago? There is already waning immunity and that waning immunity decreased the effectiveness of the vaccine to protect us against COVID-19," he said.

"Maski may exposure, mataas protection against severe disease. In fact na-experience natin on ground, fully vaccinated, wala naman nag-severe sa healthcare workers, may severe 75, 80 years old, Sinovac, age group na borderline protection," he added.

[Translation: Despite exposure, there's a high protection against severe disease. In fact

we have experienced this on the ground, we saw that fully vaccinated healthcare workers did not get severely sick. The severe cases are those in the 70-85 age group with borderline protection]

The Duterte administration has ordered 27 million doses of Sinovac, the country's largest stockpile. Last week, the government announced that it used 26 million shots procured from Chinese manufacturer Sinovac.

The Food and Drug Administration said 6.4 million people have been fully vaccinated with Sinovac shots as of Aug. 22, while 4 million received at least one dose of this vaccine brand. It accounts for nearly half of the total number of fully vaccinated individuals in the country.

Solante also weighed in on the brand of vaccine that should be used as booster shot as the more contagious Delta variant spreads across the country. He said that if majority of Filipinos are infected with the feared variant, Sinovac may not be the best one to be used as booster shot.

He also stressed that there is a need to recalibrate the kind of booster shot that will be given to healthcare workers who are most exposed to the virus and to senior citizens who are more vulnerable.

"If majority of the Filipinos have the variants, then we cannot totally rely on just getting the Sinovac at this point in time," he said. "Baka kailangan ng ibang bakuna, mas higher efficacy than Sinovac ang ibibigay sa elderly.

[Translation: Perhaps we need another vaccine with a higher efficacy than Sinovac, and we should give it to the elderly.]

"Definitely we need booster for those fully vaccinated with Sinovac to maintain protective efficacy," he added.

A steady supply of Pfizer and Moderna vaccines, however, remains a problem.

"Isang factor diyan ang supply. If there will be more Sinovac vaccines coming, then wala tayong choice but to have a third dose of Sinovac," he said.

[Translation: One factor is the supply. If there will be more Sinovac vaccines coming, then we have no choice but to give third dose of Sinovac.]