|China’s COVID vaccines have been crucial — now immunity is waning
China’s CoronaVac and Sinopharm vaccines account for almost half of the 7.3 billion COVID-19 vaccine doses delivered globally, and have been enormously important in fighting the pandemic, particularly in less wealthy nations.To get more news about sinopharm vaccine latest update, you can visit shine news official website.|
But as the doses mount, so have the data, with studies suggesting that the immunity from two doses of either vaccine wanes rapidly, and the protection offered to older people is limited. This week the World Health Organization announced advice from its Strategic Advisory Group of Experts on Immunization (SAGE) that people over 60 should receive a third dose of the same or another vaccine to ensure sufficient protection. The recommendation is “sensible and necessary”, says Manoel Barral-Netto, an immunologist at the Oswaldo Cruz Foundation in Salvador, Brazil.
A number of countries are already offering third doses to all adults or are trying mix-and-match approaches. Some experts are even questioning whether China’s jabs — based on inactivated virus — should continue to be used at all when other options are available.
But others say that the vaccines still have a major part to play. “These are not bad vaccines. They’re just vaccines that haven’t been optimized yet,” says Gagandeep Kang, a virologist at the Christian Medical College in Vellore, India, who advises SAGE.CoronaVac, produced by Beijing-based company Sinovac, is the world’s most widely used COVID-19 vaccine. Not far behind is the vaccine developed in Beijing by state-owned Sinopharm (see 'The race to vaccinate').
In mid-2021, the World Health Organization (WHO) approved the shots for emergency use, on the basis of limited clinical-trial data suggesting that CoronaVac was 51% and Sinopharm 79% effective at preventing symptomatic disease. This was on a par with the 63% efficacy reported for the University of Oxford–AstraZeneca’s viral-vector vaccine at the time of its WHO listing, but lower than the 90% and higher efficacies of the mRNA vaccines developed by Pfizer–BioNTech and Moderna.
Both the Chinese vaccines are inactivated vaccines, which use killed SARS-CoV-2 virus. Researchers say this type of vaccine seems to be less potent because it triggers an immune response against many viral proteins. By contrast, mRNA and viral-vector vaccines target the response to the spike protein, which is what the virus uses to enter human cells.
“You don’t choose the target with inactivated vaccines, you just throw in all these different antigens,” explains Jorge Kalil, a physician and immunologist at the University of São Paulo Medical School, Brazil. About 2.4 billion doses of the Chinese vaccines have been administered in China, but almost 1 billion doses have gone to 110 other countries (see 'Biggest takers for China's vaccines'). Reports earlier this year of COVID-19 surges in several countries that had vaccinated many people with these vaccines — such as the Seychelles and Indonesia — prompted questions about the protection they offered.Some studies have found that compared with vaccines made using other technologies, China’s inactivated vaccines initially generate lower levels of ‘neutralizing’ or virus-blocking antibodies — considered a proxy for protection — and that these levels drop quickly over time.
One study of 185 health-care workers in Thailand1, not yet peer-reviewed, found that 60% had high levels of neutralizing antibodies one month after receiving a second dose of CoronaVac, compared with 86% of those who had received two shots of the Oxford–AstraZeneca vaccine.
Co-author Opass Putcharoen, an infectious-diseases specialist at the Thai Red Cross Emerging Infectious Diseases Clinical Center in Bangkok, says the team also found that three months after receiving the second CoronaVac shot, the antibody prevalence dropped to just 12%.
But “waning of antibodies isn’t necessarily the same as waning of immune protection”, says Ben Cowling, an epidemiologist at the University of Hong Kong. He says that vaccines induce complex immune responses, including B cells and T cells, which might be more long lived than neutralizing antibodies.
One study from Hong Kong2, which has not been peer-reviewed, showed that CoronaVac induces a significantly lower antibody response compared with Pfizer–BioNTech’s mRNA jab one month after two doses, but that the T-cell response was comparable.
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