Rapid mRNA vaccination effectively controls SARS-CoV-2 transmission in long-term care facilities

Vaccine rollouts all over the world are aimed at cutting short the coronavirus disease 2019 (COVID-19) pandemic by inducing antibody-mediated immunity to the virus. A new study, recently released on the medRxiv* preprint server, addresses the successful reduction in viral spread and case incidence among residents of long-term care facilities (LTCF).

The first two vaccines to receive emergency use authorization (EUA) in the USA and Europe were the messenger ribonucleic acid (mRNA) vaccines from Pfizer-BioNTech (BNT162b2 vaccine) and Moderna. These platforms use nucleic acid to encode the viral spke antigen, which is not only immunodominant but plays a major role in mediating viral entry into the target host cell.

The use of mRNA allows the viral antigen to be produced correctly, so as to optimize its expression in the host after vaccination. These have claimed an efficacy of 94-95% against symptomatic disease, hospitalizations and mortality due to COVID-19, in clinical trials.

Study aims

Deaths from COVID-19 have been disproportionately high among older adults (over 80 years of age). A large share of this mortality has occurred among LTCF residents, who have a seven-fold higher risk of dying from the infection than the average American.

As a result, they have been prioritized for vaccination. The current study, set in Catalonia, Spain, aims to measure the early results of the Pfizer vaccine on the risk of SARS-CoV-2 spread and death in this population group.

This will add to the real-world observational data on post-vaccination viral transmission, which could further help improve vaccine efficacy assessments.

Study details

All participants had received two doses of the vaccine, after which all suspected cases were confirmed by reverse transcriptase polymerase chain reaction (RT PCR) or rapid antigen testing. These were assumed to be sufficiently sensitive to capture the majority of infections.

Deaths due to the infection had to be associated with either a positive test or with defined clinical and epidemiological criteria. The period of vaccine efficacy evaluation was from February 6 to March 28, 2021, since 70% of the residents would have received two doses by then and thus crossed the threshold of population immunity.

At this level, the free transmission of the virus is thought to be blocked.

They constructed models to provide a calculated prediction of the number of cases and deaths, which were compared with the actual observations over the same period.

What were the results?

The vaccination coverage in this region reached over 95% of LTCF residents within two months. This extensive coverage prevented 75% of infections, as measured by the number of documented cases and the same proportion of deaths.

Counting from two weeks after the 70% immunization threshold (with two doses of the vaccine) was reached for LTCF residents, the transmission was detected to have fallen by 70% the first week, 55% the second week, 50%, 70% and 90% with each subsequent week.

What are the implications?

The findings that three of every four predicted deaths due to COVID-19 were prevented by pushing vaccination coverage to over 70% confirms the vaccine efficacy reported in clinical trials and available observational studies.

In fact, viral transmission was reduced by 3-10-fold within a month of reaching this vaccination threshold.

An LTCF is a closed system, for the most part, and the virus is usually introduced from outside, by staff, or spread from one inmate to another. Further research should explore vaccine efficacy in other facilities and settings where infection rates are almost completely documented.

Secondly, patients staying in LTCFs are typically older and sicker, with multiple debilitating underlying medical conditions. Given the significant benefit of vaccination in this high-risk population, the researchers suggest that the actual benefit may still be higher, as the transmission and mortality rates may have been higher than estimated. Also, seasonal variations and the emergence of more dangerous variants could have pushed up the mortality rate recently.

“Our analyses provide evidence that vaccination may be the most effective intervention in controlling SARS-CoV-2 spread and subsequent risk of death available to date.” If validated, these findings point to the need to execute rapid and extensive vaccine coverage campaigns as an effective and achievable approach to ramp down the pandemic and enable a return to a more normal lifestyle.

*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.

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.