Sinovac and the Delta variant in the Philippines
By: Michael David Sy
Tags: Sinovac, Thailand, Malaysia, Philippines, Covid 19

The Department of Health has announced eleven new local cases of the Delta variant here in the Philippines. This is particularly concerning because the variant has ravaged even countries which are more affluent and more prepared than the Philippines: countries that have been great at the COVID elimination strategy have been afflicted by it (Taiwan, Australia and Vietnam).

The central issue here in the Philippines is that two of the foundations of an effective pandemic response are sorely lacking. More than a year into the pandemic, there is still a lack of a nationwide contact-tracing application, and testing still remains anemic.

Just one case of the Delta variant from an asymptomatic and infected flight crew driver triggered the current surges that Australia is experiencing. That’s already with world-class contact tracing, testing and sequencing.

Imagine what eleven cases that have been belatedly reported could do in a country without appropriate contact tracing and testing.

While I laud the strict border controls imposed here in the Philippines, the reality is that there are now local cases of the more infectious Delta variant. Vaccinations have peaked, which is good, but the reality is that most of the vaccines that have been and will be administered are Sinovac vaccines.

Sinovac remains effective against severe disease, but newer studies have corroborated the decision of Malaysia to stop giving Sinovac vaccines. Thailand, on the other hand, will perform heterologous boosting with AstraZeneca to all those initially given Sinovac vaccines.

In a recent pre-print, Sinovac was observed to generate even fewer neutralizing antibodies than natural infection. The study noted: “We next assessed NAb-afforded protection against all 4 strains in our cohorts. Overall, the percentage of participants with quantifiable NAb titers above or equal to 20 units (the NAb positivity cut-off) was highest against the WT strain (99.17%), followed by Alpha (85.83%), and Beta (82.50%), and was lowest for the Delta strain (69.17%). This pattern was consistently observed for all cohorts and, notably, the percent of individuals with detectable NAbs were lowest in CoronaVac vaccinees compared to naturally infected groups.”

Natural infection was more protective than Sinovac vaccination in terms of neutralizing antibody generation.

Although Coronavac was able to neutralize the Alpha variant, “[w]orryingly, the Delta strain, which is the most transmissible, possibly among the most virulent of all VOCs identified to date, and is rapidly becoming a dominant strain in many countries, appears to be most refractory to neutralization.”

Basically, the neutralizing antibodies that Sinovac produces are unable to address the Delta variant.

Further, in a comparative study between Pfizer and Sinovac, it was discovered that Pfizer generates ten times more neutralizing antibodies than Sinovac (269 vs 27). Neutralizing antibodies correlate to immune function, so the low levels of Sinovac are particularly telling.

An immediate measure to stall the spread of the Delta variant would be to extend the quarantine of all incoming passengers to the Philippines to 14 days. That is what Australia did. Even then, however, it still had a hard time dealing with that ONE index case.

Shifting toward more effective vaccines (Pfizer/AZ/Novavax/Moderna) will also be a better strategy for the longer term. Despite the lack of studies, I believe that the agile decision made by Malaysia and Thailand will bode better for them. Now that we’ve seen that Sinovac has low effectiveness against the variants, we should shift toward providing better vaccines to our health workers and the most vulnerable.

Right now, we already average 5,000 cases without the Delta variant. I don’t think we should wait for another India or Indonesia to happen before acting.