Current vaccines offer "low protection" against the coronavirus but mixing different doses of alternatives could help boost effectiveness, China's top disease control official has said.
Vaccine efficacy rates need to be improved, Gao Fu, director of the Chinese Centre for Disease Control and Prevention, said at a conference on Saturday, in rare comments from a senior Chinese health official claiming that current vaccines may be insufficient to halt the pandemic.
Explaining the factors that reduce vaccine effectiveness, Mr Gao said that the intervals between first and second doses need to be carefully considered.
"I suggest that we consider adjusting the vaccination process, such as the number of doses and intervals and adopting sequential vaccination with different types of vaccines," Mr Gao said in a presentation on Chinese Covid-19 vaccines and immunisation strategies, in China's south-western city of Chengdu.
“We will solve the issue that current vaccines don’t have very high protection rates. It’s now under consideration whether we should use different vaccines from different technical lines for the immunisation process.”
China's Sinovac Covid-19 vaccine being administered around the world
He also praised the benefits of mRNA vaccines – the technology behind the two Covid-19 vaccines seen as the most effective, Pfizer-BioNTech and Moderna – months after questioning whether the then-unproven method was safe.
While many vaccines introduce a weakened or inactivated germ to trigger an immune response – producing antibodies, mRNA vaccines teach the body's cells to make a protein that triggers the immune response.
"Everyone should consider the benefits mRNA vaccines can bring humanity," Mr Gao said. "We must follow it carefully and not ignore it just because we already have several types of vaccines already."
Chinese health officials at a news conference on Sunday did not respond directly to questions about Mr Gao's comments or about possible changes in official plans.
However, another China CDC official said Chinese developers are working on mRNA-based vaccines.
“The mRNA vaccines developed in our country have also entered the clinical trial stage,” said the official, Wang Huaqing. He gave no timeline for possible use.
Mixing Covid-19 vaccines
Experts say mixing vaccines – known as sequential immunisation – might boost effectiveness.
Researchers in Britain are studying a possible combination of Pfizer-BioNTech and the AstraZeneca vaccine.
Chinese vaccine effectiveness
China currently has five vaccines in use in its mass immunisation campaign, three inactivated-virus vaccines from Sinovac and Sinopharm, a one-shot vaccine from CanSino, and the last from Mr Gao’s team, in partnership with Anhui Zhifei Longcom.
The effectiveness of the vaccines range from just over 50 per cent to 79 per cent, based on what the companies have said.
The vaccine co-produced by Mr Gao's team was given emergency use approval a month ago. The team behind it have not yet publicly disclosed data about its efficacy.
Pfizer's and Moderna's vaccines have both been shown to be about 95 per cent in protecting against Covid-19 in studies, although this varies among age groups and depending on Covid-19 variants.