Sinovac vaccine recipients with low antibody levels against the coronavirus will get a “significantly higher” immunity boost if they choose the BioNTech jab as their third dose, according to Hong Kong researchers.
The first local head-to-head study of its kind also found that the German-made BioNTech vaccine generated markedly higher levels of “specific neutralising antibodies” against the more infectious Delta variant. The vaccine co-developed by Pfizer showed 95 per cent efficacy against the variant compared with 48 per cent from the Chinese-produced Sinovac shot.
The findings from University of Hong Kong and Chinese University researchers, released on Thursday, may encourage Hongkongers to opt for a BioNTech third dose as the city prepares to launch its booster programme, with bookings opening on Friday. The elderly and vulnerable are first in line for the extra doses from next Thursday.
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Separately, Macau authorities gave out advice on third and fourth vaccine doses, saying that extra shots should cover immunocompromised people aged 12 or above. The third dose should be given at least 28 days after the second shot, while the fourth one should be administered six months after the third jab.
Referring to the BioNTech and Sinovac jabs by their brand names respectively, the Hong Kong researchers said: “Our … study shows the BNT162b2 booster dose for those people who responded poorly to the previous vaccination of CoronaVac is significantly more immunogenic than a CoronaVac booster.”
The government-funded study – led by professors David Hui Shu-cheong and Malik Peiris – evenly divided 80 recipients of the Sinovac jab with low antibody levels into two groups, with each set assigned one of the two locally available jabs. The participants of the study running between August and October were aged from 34 to 73.
One month after the third dose was administered, the academics found a “significantly higher” antibody response in those given the BioNTech jab.
Immunity levels offered by the BioNTech vaccine against the Delta, Gamma and Beta variants were 95.33 per cent, 92.51 per cent and 92.29 per cent respectively. The corresponding percentage figures for the Sinovac vaccine were 48.87, 32.22 and 38.79.
Their effectiveness against the original type of the coronavirus was estimated at 96.83 per cent for BioNTech versus 57.75 per cent for Sinovac.
More participants from the BioNTech group reported discomfort and swelling at the injection site as well as fatigue and muscle pain than those who received Sinovac as the third dose. But the researchers said the adverse reactions were only mild and short-lived.
Hui confirmed the findings to the Post, and said the paper was being reviewed by the American Journal of Respiratory and Critical Care Medicine for publication.
A recent study in Turkey involving 68 medical staff double vaccinated with the Sinovac dose found their spike protein response, a key instrument to enter and penetrate virus cells, increased 46.6 times if they were given the BioNTech version as a third jab, as opposed to 1.7 times from Sinovac.
Respiratory medicine specialist Dr Leung Chi-chiu said he believed the study could help convince some vaccine doubters, especially as the findings clearly showed the benefits for those with low protection such as the immunocompromised.
But he said more time and research were needed to look at how protection levels would fare after half a year or a year, as immunity waned over a longer period.
He also warned that the small sample size of 80 in the trial might not fully reflect the occurrence or seriousness of potential adverse reactions to the vaccine.
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