Why Sinovac is inferior
As of today, July 9, 2021, the Philippines has acquired a total of 20,607,570 vaccine doses. 11,000,000 doses were from Sinovac, which represents 96% of all the procured vaccines. It is 58.2% of all vaccines available in the Philippines.
The Philippines were in talks to procure 10M doses of Pfizer during the second half of last year, but that wasn’t realized because of incompetent officials. Despite issues with respect to data and price, Sinovac had been procured by the government. Issues were raised with respect to its lower efficacy, which was close to the WHO cutoff. Further, there were no studies to support its use in the elderly, and the Philippine FDA provided recommendations that it was to be used only for people aged 18–59 years. They would backtrack later on, however, and allow for its use in healthcare workers and the elderly.
Studies done on its effectiveness on healthcare workers, however, have shown that it is only 37% effective after two doses in a Manaus, Brazil study, where high Gamma variant transmission was occurring. In another Brazilian state, vaccine effectiveness on healthcare workers in Roraima, Brazil, was 50.7% two weeks after the second dose, which closely approximated the 50.38% efficacy from the Phase III trial results.
The initial decision of the Philippine FDA truly reflected what the data had shown. Because of the global supply limitations, however, it was later revised for Sinovac to be administered even to healthcare workers and the elderly.
Nevertheless, better real-world results from Chile were recently released. Against symptomatic disease, Sinovac was 63.6% effective against symptomatic infection, and 86.5% protective against hospitalization, and 86.7% protective against death. While Sinovac has lower efficacy when it comes to symptomatic infection, it was found effective against severe disease.
Recent reports, however, from nations who have predominantly relied upon Sinovac observed that there was still an absolute rise in cases and deaths. Indonesia is currently suffering from a spike in cases despite having almost twice the rate of fully vaccinated individuals (5.35% vs. our 2.82%). The only available vaccine for them is Sinovac: “Sinovac is the only choice”.
There have been studies beforehand by David Khoury, et. al, with respect to the link between vaccine efficacy and neutralizing antibody generation. Basically, the lower the vaccine efficacy, the fewer neutralizing antibodies generated. This was, however, more of a model that predicted that a vaccine with 50% efficacy would only be protective for a few months.
It didn’t even take into consideration that the older a person was, the less effective his or her immune system would be. Also, it didn’t take note of the rise of the variants!
With the mRNA vaccines Pfizer and Moderna, even if the neutralizing antibodies were reduced due to age AND the adaptations of the variants, it would still be 75–90% effective against the variants of concern.
But what if the starting efficacy against the original virus was only 50%?
That is Sinovac’s conundrum.
Now, a recent article published by the Lancet showed that after 134 days, Sinovac barely has neutralizing antibodies that function against the major variants of concern. Recall that the Alpha, Beta, and Delta variants are all of B lineage. The Gamma variant is from the P lineage. This means that all four major VOCs are covered by this study.
The limited time period which Sinovac functions against the B lineage of variants (Alpha, Beta, and Delta) lasts only for 3–4 months (96–117 days). After full immunization (2 weeks after the second dose), it loses neutralizing antibodies from the fourth month onward (Diagram D), and is barely effective (the black circle is the median of neutralizing antibodies, and Sinovac lies below the cutoff, which is represented by the dotted line). Sinovac has also been observed to be ineffective against the Gamma variant, as could be seen in Diagram C and D below.
Deciding to be immunized here in the Philippines where booster doses will not be entertained for the time being will be a choice of having some protection immediately with Sinovac, or waiting for the better vaccines such as Pfizer, Moderna, or AstraZeneca, with more extensive and prolonged protection.
I chose the latter, because I adhere to evidence-based medicine. Pfizer, Moderna, and AstraZeneca all have evidence against the major variants of concern, and have a persistent presence of neutralizing antibodies.
I recommend everyone to be immunized, of course, but also question the fondness of the Philippine government for Sinovac. Later this month, eight million more doses will arrive. The data is now there. Can we still really say that “all vaccines are equally effective?”
