Efficacy data of CoronaVac in Turkey – Authors’ response

We thank Martina McMenamin and Benjamin Cowling for raising important questions about vaccine trials in the context of our article.

The work to which they refer by Palacios and his colleagues

has not been published in a peer-reviewed journal; therefore, we cannot comment on the accuracy or comparability of its methods. Data from Indonesian trials has been published,

and although the primary method for this study was similar to ours, the COVID-19 case definition and methods used for active surveillance were different. Only 1,620 volunteers were included, but over a longer follow-up period (approximately 2.5 months) preventing a direct comparison of the primary endpoint.

Nonetheless, the efficacy of CoronaVac against serious illness in this study was 100% as there were no critical cases or deaths attributable to COVID-19, which is undoubtedly similar to our results.

Regarding post-vaccination neutralizing antibody titers in the immunogenicity subset of our trial, the seroconversion rate was 89.7% in the vaccinated group, of which 92% had neutralizing antibodies. This result could translate into a positivity of neutralizing antibodies of 82.5% in these volunteers. The efficacy against symptomatic disease reported at 83.5% is consistent with this immunogenicity result. We have carried out active surveillance to detect COVID-19 in patients; However, as the primary outcome measure was symptomatic COVID-19, it is indeed possible that we missed asymptomatic patients. In fact, most COVID-19 vaccine trials aim for a similar outcome, focusing on effectiveness in preventing symptomatic and serious illness rather than preventing infection. We were aware of the short follow-up period in our interim review and therefore discussed it as a major limitation of the article,

indicating that the study would not allow commenting on long-term protection.

Real-world efficacy data from pragmatic study designs will add value to Phase 3 trials to see vaccine performance in unselected populations, as complementary studies rather than concurrent. For example, Jara and her colleagues

reported analysis of actual data from Chile, including approximately 10.2 million people vaccinated with CoronaVac. The adjusted vaccine efficacy among fully immunized individuals was 65.9% (95% CI 65.2 to 66.6) for the prevention of COVID-19 and 87.5% (86.7 to 88 , 2) for prevention. admission to hospital.

During a pandemic where only 2.3% of people in low-income countries had received at least one dose of a COVID-19 vaccine by October 2021, every effort to make safe COVID-19 vaccines available is valuable . We believe our data is an important contribution to the scientific literature in a world where we can no longer establish randomized, placebo-controlled trials for COVID-19 vaccines for ethical reasons. The way forward to building confidence in vaccines is to communicate real world data transparently.