The ongoing coronavirus disease 2019 (COVID-19) pandemic has been caused by the rapid outbreak of the severe acute respiratory coronavirus 2 (SARS-CoV-2). Scientists have developed novel vaccines, and vaccination programs have commenced in many countries. In Italy, the program started in December 2020, and the available vaccine was the BNT162b2 mRNA vaccine (Cominarty).
Study: BNT162b2 mRNA COVID-19 Vaccine Effectiveness in the Prevention of SARS-CoV-2 Infection and Symptomatic Disease in Five-Month Follow-Up: A Retrospective Cohort Study. Image Credit: cortex-film/ Shutterstock
A new study has been published in the journal Vaccines that evaluated the effectiveness of Cominarty against documented SARS-CoV-2 infection and symptomatic diseases in the medium to long term.
A new study
A mass vaccination campaign was initiated in Italy and other European countries on December 27, 2020. Healthcare workers (HCWs) were prioritized for vaccination by the Italian government as they were at high risk of contracting the virus. The vaccine was administered to individuals 12 years of age and older, at least 21 days apart. In the pre-licensure trial, the vaccine (Pfizer-BioNTech) was 95% effective in preventing COVID-19 and did not have any significant side effects.
The cohort study was conducted at Bari Policlinico General University Hospital, comprising 1000 beds and 6000 health care workers (HCWs). HCWs who completed the vaccination schedule were matched with HCWs who had refused vaccination, and the two groups were followed up for five months (January–May 2021). The medium- to long-term effectiveness of BNT162b2 was evaluated.
The study population comprised 6136 HCWs, out of which 5351 were in the vaccinated group. The median time between the first and second doses was 23 days. The results obtained for this population were compared to those of a previous report by the same authors, which was carried out in Apulia (with about 4,000,000 inhabitants). In Apulia, from February 2020 to July 7, 2021, 253,571 confirmed cases of COVID-19 and 6646 related deaths were reported.
The median follow-up period was 139 days, during which there were 227 cases of SARS-CoV-2 infection. One hundred seventy-nine infections were noted in the unvaccinated group, and the cumulative incidence was 2.8 per 10,000 person-days. The symptomatic disease developed in 131 HCWs, including 112 in the unvaccinated group. In this case, the cumulative incidence was 1.6 per 10,000 person-days. There was considerable heterogeneity, with the cumulative incidence in the unvaccinated group being 12.4 per 10,000 person-days and 0.3 per 10,000 person-days in the vaccinated group.
The cumulative incidence of both infection and symptomatic disease in the two groups was substantially lower in the vaccinated group. The vaccine efficacy was also estimated, and scientists observed nine hospitalizations, including eight in the unvaccinated group and one in the vaccinated group. During vaccination follow-up, there were no serious and/or long-term adverse reactions. The safety of the vaccine is the subject of a report currently in preparation.
Strengths and limitations
The study's main strengths were the large sample size and a longer follow-up period compared to others in the literature.
The main limitation was the inability to break down vaccine effectiveness based on age, sex, ethnicity, etc. Furthermore, no data on the circulating virus variants were available. Therefore, these results should be interpreted as those for variants less infectious than the Delta variant. Scientists also opine that it could well be the case that some asymptomatic infection was not detected. Lastly, the immune status (es. immunodepression, chemotherapy treatment, etc.) of enrolled subjects was not available.
The data presented in this analysis are consistent with the very high effectiveness of the BNT162b2 mRNA vaccine in preventing both SARS-CoV-2 infections. In another study, scientists reported the production of 100% neutralizing antibodies after the second dose and well-tolerated adverse effects. Of course, other studies have reported low efficacy of BNT162b2 in preventing the transmission of variant B.1.1.7. The results, overall, should encourage vaccination among still-reluctant HCWs.
In Italy, vaccination of HCWs is still not mandatory, but given the severity of the pandemic, this policy merits serious deliberation. In March, the Italian government made vaccination semi-compulsory with penalties related to salary suspension.
However, more research is needed to understand the practical effects of this regulation. Further research is also required to determine the VE of the BNT162b2 mRNA vaccine in different populations and over an even longer follow-up period. That will make people more comfortable with the idea of vaccination and help us combat the COVID-19 pandemic.