Confirming Effectiveness of Inactivated COVID-19 Vaccines

Full vaccination with inactivated COVID-19 vaccines remained a viable option for preventing severe COVID-19 during the Delta wave of the pandemic, according to a recent study in China, which noted that partial vaccination was insufficient to protect against the variant and that booster shots may be necessary.

“Given their real-world effectiveness as well as convenient stocking and distribution, inactivated vaccines should be considered an option for immunity reinforcement programs on completion of population-level, 2-dose vaccination,” the authors, led by Min Kang, MMed, of the School of Public Health at Southern Medical University and Guangdong Provincial Center for Disease Control and Prevention, wrote.

The retrospective cohort study, published in the Annals of Internal Medicine, included 10,805 people with SARS-CoV-2 infection and close contacts in Guangdong, China, during the Delta variant outbreak in May and June of 2021. All people included in the study were linked to a single COVID-19 index case, with exposure identified by contact tracing.

Among the study participants, 5888 (54.5%) were unvaccinated, 2286 (21.1%) had an intermediate first dose of HBO2 or CoronaVac COVID-19 vaccines, 841 (7.8%) were partially vaccinated, 387 (3.6%) had an intermediate second dose, and 1403 (13.0%) were fully vaccinated.

Among those who were fully vaccinated, vaccine effectiveness was 51.8% (95% CI, 20.3% to 83.2%) against infection, 60.4% (CI, 31.8% to 88.9%) against symptomatic infection, 78.4% (CI, 56.9% to 99.9%) against pneumonia and 100% (CI, 98.4% to 100.0%) effective against severe or critical illness.

Vaccine effectiveness dropped off significantly among those were who were only partially vaccinated at 10.7% (CI, −41.2% to 62.6%) against infection, 6.8% (CI, −47.4% to 61.0%) against symptomatic infection, and 11.6% (CI, −42.6% to 65.8%) against pneumonia.

“No severe or critical cases occurred among vaccinated participants,” the study authors wrote. “By contrast, unvaccinated participants had 19 (0.3%) severe or critical cases.”

Still, the study noted that inactivated vaccines may not be equally effective against Delta and other variants. Waning effectiveness suggests that booster shots may be necessary.

“Preventing symptomatic infections remains an important task of global public health efforts because symptomatic patients are the ones suffering from illness and requiring medical attention,” the authors wrote.

The study didn’t break apart data on the 2 brands of inactivated vaccines included and cannot determine if vaccine effectiveness applies equally to both brands.

Inactivated vaccines account for about half of the COVID-19 vaccines that have been distributed. Studies showing diminished effectiveness against variants have caused some investigators to question their role in global vaccination strategies.

Global health leaders are working to develop a long-term strategy for COVID-19 vaccines and boosters as the pandemic evolves.