Chinese scientists have suggested an additional shot of a COVID-19 vaccine developed by domestic pharmaceutical company Sinovac could prove beneficial in the fight against the coronavirus.
A third dose of the vaccine, dubbed CoronaVac, could increase antibody levels in fully vaccinated individuals by at least threefold if administered six or more months after receiving the recommended two shots, experts said in a new paper. The study was published Sunday as a preprint, meaning it hasn’t been vetted by independent experts.
The small-scale trial involving 540 participants in China found a notable drop in their antibody levels six months after vaccination. Although the level of antibodies required to prevent COVID-19 is unclear, a higher antibody count is generally associated with stronger protection against viruses, according to an immunologist, who requested anonymity, as they were not authorized to speak to the media.
“More antibodies circulating in the blood to fend off the virus means even if people get infected, they tend not to have symptoms, lowering the risk of spreading the virus to others,” the immunologist told Sixth Tone.
The suggestion for a booster shot comes when China is facing a local outbreak in the eastern city of Nanjing, which experts have attributed to the highly infectious Delta variant of COVID-19. Since the first cases were identified among workers at the city’s international airport last week, the virus has now spread to at least 13 cities, including the capital Beijing.
Many of the airport workers in Nanjing were said to be vaccinated, though it’s unclear which of the five approved vaccines they had received. Medical experts said the chance for infected patients to develop severe COVID-19 symptoms was “significantly lower.”
CoronaVac is said to be about 66% effective in preventing COVID-19 and 86% in preventing COVID-19-related deaths among individuals 16 years or older, according to real world data from Chile.
While Sunday’s study didn’t reveal if CoronaVac’s efficacy would change over time, data from other COVID-19 vaccines suggested diminishing protection over time. For example, the efficacy of the Pfizer-BioNTech vaccine, one of the world’s most effective shots, fell from 96% to 84% over six months, a preprint published Wednesday revealed.
As countries around the world battle recurrent surges in COVID-19, compounded by new variants, relaxed restrictions, and the waning efficacy of vaccines, governments in some high-income countries such as the United States and United Kingdom are weighing in on the need for booster shots. However, representatives at the World Health Organization (WHO) oppose the idea of booster shots, saying there isn’t enough evidence to suggest fully vaccinated people would require one for months.
“It may well be that you need boosters after a year or two years,” the WHO’s chief scientist, Soumya Swaminathan, said earlier this month. “But at this point, at six months after the primary dose, there doesn’t seem to be any indication.”
While discussions on a booster shot are gaining momentum in some countries, the disparity in access to vaccines continues to become more apparent. Only 1.1% of the population in low-income countries have received at least one dose of COVID-19 vaccine, according to Our World in Data.
Contribution: Nie Yiming; Editor: Bibek Bhandari.
(Header image: A health worker prepares to administer Sinovac’s COVID-19 shot at a vaccination center in Tanggerang, Banten, Indonesia, July 28, 2021. Dimas Ardian/Bloomberg via Getty Images/People Visual)