Sinopharm shares phase 2 data on inactivated COVID-19 vaccine

Sinopharm has published clinical data on its adjuvanted SARS-CoV-2–inactivated virus vaccine. The phase 1 and 2 results suggest the vaccine may be safe, tolerable and capable of triggering production of antibodies against the pandemic coronavirus.

Most of the frontrunners in the COVID-19 vaccine race are using relatively unproven approaches to immunization. BioNTech, in partnership with Pfizer, and Moderna are advancing mRNA vaccines, a type of prophylactic that has never been approved. AstraZeneca, CanSino and Johnson & Johnson are taking a viral vector approach that is barely more established than mRNA.

Sinopharm and fellow Chinese’ vaccine developer Sinovac are at the forefront of efforts to develop a more traditional inactivated virus shot against SARS-CoV-2. Both companies moved their prospects into phase 3 without sharing much information on their effects publicly.

That changed on Thursday when JAMA published an analysis of phase 1 and 2 trials of Sinopharm’s vaccine. The paper presented data from a 96-subject phase 1 that assessed three doses, as well as a 224-subject phase 2 that provided further evidence of the effects of the middle dose.

The trial linked the vaccine to increases in antibody titers. However, unlike other COVID-19 vaccine trials, the study lacked a comparison arm featuring serum samples from patients previously infected with the coronavirus, complicating the task of interpreting whether the response is likely to confer immunity. 

The authors compared the antibody response favorably to the results of other vaccine trials, stating the levels were in the same ballpark as those generated by shots in development at AstraZeneca, BioNTech and Moderna. However, as the authors acknowledge, differences in assay methods and other aspects of the trials mean “such direct comparisons should be interpreted cautiously.”

Like most of the other leading vaccines, Sinopharm’s candidate looks likely to require a booster shot to provide protection, diminishing the company’s immunization capacity and complicating the task of vaccinating large numbers of people. Those problems could be particularly acute for the Sinopharm vaccine. The strongest antibody response was seen after the third injection. 

Sinopharm looked at the distribution of subsets of blood lymphocytes, such as CD3+CD8+ T cells, in subjects before vaccination and multiple times thereafter. The analysis showed “no notable changes over time in different groups or substantial differences across groups at a certain time point.”

Safety is an area Sinopharm thinks it might have an edge. With 15% of subjects experiencing adverse reactions, the authors argue the Sinopharm prospect has “a relatively better safety profile compared with vaccines using other platforms.”

Sinopharm is well on its way to showing if the perceived benefits stand up to the scrutiny of a larger study. A phase 3 trial is underway. The trial will enroll 15,000 subjects across three cohorts, according to its listing on China’s registry. According to a recent media report, sites in the United Arab Emirates have already administered the vaccine to more than 5,000 people.