The effectiveness of mRNA BNT162b2 vaccine in reducing severe COVID-19: Evidence from Germany

The coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). In Germany, the mortality rate due to COVID-19 between January 2020 to February 2021 was less than 0.1% among individuals below 50 years of age.

However, conditions in nursing homes were quite different, with the mortality rate reaching as much as 13%. Hence, this group was prioritized for vaccination, which commenced in December 2020 in Germany.

Study: Two doses of the mRNA BNT162b2 vaccine reduce severe outcomes, viral load and secondary attack rate: evidence from a SARS-CoV-2 Alpha outbreak in a nursing home, Osnabrueck, Germany, January-March 2021. Image Credit: SeventyFour / Shutterstock.com

Impact of the SAR-CoV-2 Alpha variant among nursing home residents and staff

A new study published on the preprint server medRxiv* discusses the epidemiology of the outbreak in German nursing homes and the preventive measures undertaken. The researchers also determined vaccine effectiveness (VE) against the SARS-CoV-2 Alpha variant by analyzing its effect on severe outcomes that required hospitalization or caused death. Additionally, the effect of the vaccine on viral load and secondary transmission was also analyzed.

This retrospective cohort study included all staff and individuals residing permanently or as day-care residents in the nursing home who were found to be COVID-19 positive via a reverse-transcriptase polymerase chain reaction (RT-PCR) test between early January and mid-March 2021.

The nursing home comprised a day-care that was occupied by 24 persons, as well as seven permanent care wards consisting of 100 residents. A total of 128 members of staff were associated with the facility, all of whom were included in this study.

In this study cohort, 77% of residents and 56% of staff members were vaccinated with the BNT162b vaccine. All members were vaccinated within early and late January 2021 while maintaining a three-week interval between the first and the second doses.

The median age of the staff members was 49 years, whereas the median age was 87 years among residents. Taken together, 77% of the residents included in this study were male and 88% of the staff members were female.

The estimated VE of this study was lower as compared to the population-based cohort study conducted in Israel, which revealed a VE of 93% against death and 96% against hospitalization. The current study revealed that the age-adjusted VE of two doses of the BNT162b vaccine was moderate against infection and significantly high against severe SARS-CoV-2 infection. Interestingly, the authors observed that half the vaccinated individuals who contracted SARS-CoV-2 were diagnosed within 7-11 days after the second vaccination. This result indicated that individuals who were completely immunized and had sufficient time to develop antibodies were more protected against the SARS-CoV-2 Alpha variant.

This study also revealed that no significant increase in vaccine effectiveness was observed when the interval between the first and second doses of vaccine was increased. This report was in line with the findings from the analysis of the United Kingdom cohort.

Researchers used Ct values to reflect the viral load after vaccination. The current study revealed that the Ct values at diagnosis were higher with longer intervals after the second dose of the vaccine as compared to the unvaccinated group. This result did not support the previous study, which reported a reduction in the viral load four weeks after the first vaccination.

Although the transmission of SARS-CoV-2 was reduced, a high possibility of infection prevailed among individuals in close contact with vaccinated individuals with breakthrough COVID-19. This result is in line with previous studies that reported an increased possibility of infection among household members of healthcare workers with breakthrough infections and vaccinated with BNT162b2. Secondary infection was found to be 22% in households of vaccinated individuals and 67.7% in households of unvaccinated infected staff.

Strengths and limitations

One of the main strengths of this study is frequent PCR-testing of every 5-6 days throughout the study period. This minimized the chances of error of exclusion of asymptomatic cases. In the majority of the previous studies, in similar settings, an underestimation of asymptomatic infection occurred.

Some of the limitations of this study include its small sample size and exclusions of risk factors such as underlying chronic diseases. The effect of following all non-pharmaceutical preventive measures played an important role in controlling the disease. This could therefore result in a bias in the estimation of the VE. Another limitation of this study is the inability to determine whether the primary and secondary infections were related, in that both the infections were caused by identical viral strains.

Conclusion

The authors of this study believe that frequent PCR testing could help isolate infected persons in a designated ward. Individuals in contact with these patients should also be quarantined early onto prevent the further spread of the disease.

The current study emphasized the importance of two doses of the vaccine. This is because individuals with complete BNT162b vaccination showed reduced viral load and secondary transmission. Also, a decrease in the severity of infection with reduced cases of hospitalization and mortality was observed.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.

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