Pharmaniaga Bhd’s claim of lower heterologous boosting effectiveness for Sinovac primary vaccination recipients against Omicron was refuted by the Institute for Clinical Research (ICR) of the Ministry of Health (MoH).
The pharmaceutical company’s statement contradicts a tweet posted by Health Minister Khairy Jamaluddin last November, which stated that “for Sinovac recipients, a Pfizer booster is the best choice to increase your level of protection”.
The current facts and evidence cited by Pharmaniaga in its statement on Feb 9, 2022, were misrepresented, according to the ICR.
“Globally, there is emerging and consistent evidence that heterologous booster vaccination results in more robust immune responses and is more effective than homologous boosting for recipients of primary series of inactivated vaccines (Sinovac),” ICR said in its statement on Feb 10, 2022.
It cited a study from the Dominican Republic that found that participants who had received two doses of Sinovac had undetectable neutralisation against the Omicron variant.
Meanwhile, compared to only two doses of mRNA vaccine, a Pfizer booster (heterologous mRNA vaccine booster) resulted in 1.4 times more neutralisation activity against Omicron.
Despite this increase, neutralising antibody titres for Omicron were still lower than for ancestral and Delta variants.
“In this study, there was no homologous booster (Sinovac) group of participants to allow comparison between heterologous and homologous boosting regimens.”
The ICR also highlighted two separate studies comparing heterologous and homologous booster regimens for Sinovac primary series recipients, conducted in Hong Kong and Brazil, respectively.
“In a study done in Hong Kong, a heterologous Pfizer booster following two doses of Sinovac improved neutralising antibody levels against Omicron at three to five weeks post-booster dose, but three doses of Sinovac failed to elicit neutralising antibody responses to the new variant in most recipients.
“In another study conducted in Brazil, heterologous booster doses with AstraZeneca, Janssen, and Pfizer vaccines resulted in more robust immune responses than homologous boosting.
“The study found that heterologous booster doses substantially increased the neutralising capacity of serum samples against both Delta and Omicron variants (at least 90 per cent seropositive after booster), compared to strikingly lower responses observed after a homologous Sinovac booster with only 35 per cent becoming seropositive against Omicron,” it said.
Khairy said at a press conference that recipients of Sinovac vaccination primer doses could choose the same brand for booster shots.
“Although MoH still believes in encouraging them to take Pfizer or AstraZeneca booster doses, taking any booster is better than no booster,” he said.