The Malaysian Insight

PHARMANIAGA Berhad has misinterpreted findings on the effectiveness of heterologous (mixing vaccines) against the Omicron Covid-19 variant for those who received the Sinovac vaccine as their primary doses, the Health Ministry’s Institute of Clinical Research said today.

It said globally, consistent evidence has shown that heterologous boosting results in better immune response and is better than homologous boosting for Sinovac recipients, the institute said, citing three studies in its response to the company’s statement.

One was a study in the Dominican Republic, which found that neutralisation against the Omicron variant was undetectable in participants who had received two doses (primary vaccination) of Sinovac. 

“A Pfizer booster resulted in a 1.4-fold higher neutralisation activity against Omicron when compared to only two doses of mRNA vaccine,” it said.

However, it also noted that in this study, there was no homologous booster (Sinovac) group of participants to allow comparison between the heterologous and homologous boosting regimen.

Another study was one in Hong Kong, which also showed that two doses of Sinovac followed by a Pfizer booster improved neutralising antibody levels against Omicron three to five weeks after the booster.

However, three doses of Sinovac failed to elicit the same response in the Hong Kong study, the institute said.

Quoting the third study, done in Brazil, the institute said heterologous boosting with the AstraZeneca, Janssen and Pfizer vaccines had resulted in stronger protection, compared to homologous boosting with Sinovac.

“The study found that heterologous booster doses of AstraZeneca, Janssen and Pfizer vaccines substantially increased the neutralising capacity of serum samples against both Delta and Omicron variants (at least 90% seropositive after booster), compared to strikingly lower responses observed after a homologous Sinovac booster with only 35% becoming seropositive against Omicron,” it said.

It also noted real world data from Chile, which observed “an adjusted vaccine effectiveness against asymptomatic Covid-19 of 78.8% for three doses of Sinovac”.

This is lower when compared to 96.5% with a Pfizer booster and 93.2% with an AstraZeneca booster – in each case following two primary doses of Sinovac.

“The observed effectiveness against hospitalisation, intensive care unit admission and Covid-19-related deaths was also higher for heterologous boosters (Pfizer and AstraZeneca) than homologous booster (Sinovac),” the institute said of the Chilean data.

It also cited data in Malaysia, where analysis of 13 million people was done comparing those who received Pfizer and Sinovac as the primary vaccines.

“Among Sinovac recipients, a heterologous booster (Sinovac primary vaccination, followed by a Pfizer booster) offered greater protection against infection than a homologous booster dose (three doses of Sinovac),” it said.

The institute’s statement comes after Pharmaniaga refuted the Health Ministry’s claim that a Pfizer-BioNTech booster would increase the level of protection against new virus variants such as Omicron, especially for those whose primary doses were the Sinovac vaccine.

The pharmaceutical company, which is the country’s sole distributor Sinovac’s CoronaVac vaccine, had relied on data from research by the producers of the Chinese vaccine, Sinovac Biotech Ltd, that reportedly showed three doses of Sinovac vaccine produced higher neutralising antibodies in 95% of recipients, compared with 3.3% by the second dose against a variant of concern, including Omicron.

The ministry has recommended heterologous boosting using Pfizer or AstraZeneca and provides these options only in its national immunisation programme.

Those wishing to take Sinovac as a booster shot, however, still have the option to do so by paying for it at private hospitals or clinics.

Health Minister Khairy Jamaluddin has said allowing this arrangement was better so that those insisting on a Sinovac booster would have a booster shot, rather than none at all. – February 10, 2022.