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Antibodies from Sinovac’s COVID-19 shot fade after about 6 months

لقاح «سينوفاك» الصيني ينتج أجساما مضادة تدوم لـ ٦ أشهر


BEIJING: Antibodies triggered by Sinovac Biotech’s COVID-19 vaccine declined below a key threshold from around six months after a second dose for most recipients, but a third shot had a strong booster effect, a lab study showed.

Chinese researchers reported the findings from a study of blood samples from healthy adults aged between 18-59 in a paper published on Sunday, which has not been peer reviewed.

Among participants who received two doses, two or four weeks apart, only 16.9% and 35.2% respectively still had neutralising antibodies above what researchers regard as a detectable threshold level six months after the second shot, the paper said.

Those readings were based on data from two cohorts involving more than 50 participants each, while the study gave third doses of the vaccine or placebo to a total of 540 participants.

Researchers said it was unclear how the decrease in antibodies would affect the shot’s effectiveness, since scientists have yet to figure out precisely the threshold of antibody levels for a vaccine to be able to prevent the disease.

Apart from durable antibodies, other components in humans immune systems such as T cells and B cell memory elicited by the vaccine may also contribute to protection, researchers involved in the study said, although the study did not provide data on those factors. “In the short-to-medium term, ensuring more people complete the current two-dose schedule of CoronaVac (Sinovac’s vaccine) should be the priority,” the paper said.

Participants in some cohorts who received a third dose of the Sinovac shot about six months after the second showed around a 3-5 fold increase in antibody levels after a further 28 days, compared with the levels seen four weeks after the second shot.

As of end-June, Sinovac has delivered more than 1 billion doses of the vaccine, a major vaccination tool in China, Brazil, Indonesia and Chile.

Other COVID-19 vaccine makers are seeking to get authorisation for booster shots. Pfizer and partner BioNTech said earlier this month they had planned to ask U.S. and European regulators within weeks to authorise a booster dose of its COVID-19 vaccine,based on evidence of greater risk of infection six months after inoculation and the spread of the highly contagious Delta variant.

Siti Nadia Tarmizi, a senior health ministry official in Indonesia, told Reuters on Tuesday that clinical data from the country showed the reduced antibody level is still enough to provide protection, without providing details.

She said the immunisation advisory board recommends a booster vaccination 12 months after the second dose.

Indonesia has started giving booster shots produced by Moderna to medical workers this month, including those who had received Sinovac doses.

Philippines’ Health Secretary Francisco Duque said on Tuesday there is no recommendation yet from the country’s vaccine expert panel on giving a booster shot but experts are discussing the possibility.

Turkey has already started offering a third dose from either Sinovac or Pfizer to some people who have got Sinovac shots.

The research paper on Sinovac’s vaccine said that the study did not test the antibodies’ effect against more transmissible variants, and that further research was needed to assess antibody duration after a third shot.

The study was conducted by researchers at disease control authorities in Jiangsu province, Sinovac, and other Chinese institutions.


بكين: كشفت دراسة معملية أن الأجسام المضادة التي ينتجها لقاح “سينوفاك بيوتيك” المضاد لكوفيد-19 انخفضت إلى أقل من مستوى مهم للوقاية بعد نحو ستة أشهر من تلقي الجرعة الثانية لدى معظم الأشخاص، لكن تناول جرعة ثالثة له أثر تنشيطي قوي، حسبما نشرت وكالة أنباء “رويترز”.

وأعلن باحثون صينيون هذه النتائج استنادا إلى عينات دم من بالغين أصحاء في المرحلة العمرية بين 18 و59 عاما في بحث نُشر يوم (الأحد) الماضي لكن لم يتم إجراء دراسات مقارنة بعد.

وقال الباحثون إنه لم يتضح كيف سيؤثر نقص الأجسام المضادة على فعالية اللقاح نظرا لأن العلماء لم يحددوا بدقة الحد الأدنى من مستويات الأجسام المضادة التي ينتجها أي لقاح وتكون كافية للوقاية من المرض.

وكشفت الدراسة أيضا أن متلقي اللقاح في بعض الفئات، الذين تلقوا جرعة ثالثة من سينوفاك بعد نحو ستة أشهر من الجرعة الثانية زادت الأجسام المضادة لديهم بنحو ثلاثة إلى خمسة أمثال ما كانت عليه بعد 28 يوما من الجرعة الثالثة مقارنة بالمستويات المسجلة بعد أربعة أسابيع من الجرعة الثانية.

لكن الباحثين حذروا من أن الدراسة لم تختبر فعالية الأجسام المضادة في مواجهة سلالات أكثر نقلا للعدوى من فيروس كورونا، مضيفين أن هناك حاجة لمزيد من البحث لقياس مدة فعالية الأجسام المضادة بعد تلقي جرعة ثالثة.

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