mRNA and Adenovirus-Vectored COVID-19 Vaccine Effectiveness Contrasted

A retrospective observational analysis published by The Lancet Infectious Diseases on January 27, 2022, investigated the effect of time since vaccine COVID-19 completion on the SARS-CoV-2 coronavirus infection and its severe forms.

This new study is based on real-world data from more than 5.3 million individuals in the Lombardy Regional of Italy who had completed the vaccination against COVID-19.

The results show that the rate of SARS-CoV-2 infection increased continuously as time from the vaccination increased.

Nearly five infections per 10,000 person-months occurred in the first month after vaccination, and the increase in Breakthrough Infections doubled at nine months after complete vaccination.

Although this study was not primarily designed for measuring vaccination effectiveness, the protection against the risk and the severity of SARS-CoV-2 virus infection was not superimposable between mRNA-based and adenovirus-vectored vaccines.

Both vaccine types exhibited increasing infection rates as time passed from the last vaccine dose.

However, the absolute difference between mRNA-based and adenovirus-vectored vaccines was much less evident for the risk of developing severe illness.

These findings strongly suggest that both the mRNA-based and the adenovirus-vectored vaccines exert a sustained protective effect against the severe forms of the SARS-CoV-2 infection.

At the same time, the mRNA type seems better equipped to prolong the initial protective effect against the risk of developing milder forms of the infection.

However, this study does not provide the factors and mechanisms involved in the faster or slower decline of the COVID-19 vaccination protective effect on the risk and severity of SARS-CoV-2 infection.

'It should be nevertheless emphasized that these considerations should be taken with caution because individual persistence of vaccine-dependent protection might vary markedly from average data,' wrote these researchers.

Note: There was no external funding for this study, nor were any conflicts of interest disclosed by these researchers.