Research Article Review-SARS-CoV-2 Infection among Vaccinated and Unvaccinated Residents

Are you tired of wearing masks? Are you tired of maintaining 6 feet from the people around you wherever you go? I mean aren’t we all at this point? Of course, we have to continue to do both until it is safe to return to normal life, but how long is that? Unfortunately, there is no easy answer to this but certainly, there is one thing that can expedite the return to normalcy: getting vaccinated. Now, vaccines have been a hot topic since the beginning of last year, and it doesn’t help that false myths and rumors are being circulated throughout various facets of the internet. So how effective are vaccines really? Well, scientists at Brown University have researched the answer to this question by conducting a study on both vaccinated and unvaccinated residents of 280 nursing homes across 21 states in the US. Read on to find out just what they discovered.


Researchers at Brown University may just have come up with the answer to the question we’ve all been asking: do vaccines really work? Will they successfully prevent the virus from entering our body and making us sick? Well, a group of scientists took a look at infection rates in both vaccinated and unvaccinated residents of senior nursing homes. Out of the people that tested positive, the scientists also compared the number of symptomatic v asymptomatic cases.


So what do we know? Well, we know that people have been getting vaccinated since December of 2020 and data accumulated since then indicates a general decline in infection rates.


Well, if we know that vaccination has indeed been influencing the decline in incidence cases since December 2020, what is the purpose of this particular study? For starters, the participants of this study comprise one of the nation’s most vulnerable populations. The median age of study participants who received at least one dose was 78 and median age of unvaccinated participants was 75.9. So if the vaccine is working, it should be able to provide reasonable protection to the participants of this study. In other words, less hospitalizations and deaths. Well that’s a good thing, right? Furthermore, the study also took into account demographic characteristics such as age and race, and clinical characteristics such as medical conditions and impairments. Additionally, it compared staff vaccination rates across all of the nursing homes and county infection rates. It should be noted, however, that immunocompromised residents, or residents with an impaired immune system, were excluded.


So what exactly were the scientists expecting to get out of this study? Well, I’m sure, just like the rest of us, they expected the number of cases to go down after vaccines came into effect. And that’s exactly what happened, but there was also something surprising about the results.


So who were the people that took part in this study? Well, as mentioned before, this study was conducted on 18,248 vaccinated and 3,990 unvaccinated residents of 280 nursing homes across 21 states with no prior history of the Covid-19 disease. Those infected 90 days prior to the study were excluded along with immunocompromised patients.


Subjects were identified in terms of three groups. Group 1 consisted of residents vaccinated with at least one dose as of February 1, 2021. Group 2 consisted of residents vaccinated with both doses by February 1, 2021(also part of Group 1). And lastly, the control group, or Group 3, consisted of the unvaccinated( as of March 31, 2021) body of the study participants.


It should be noted that although the study did compare demographic characteristics such as sex and race, age was the only control common factor because the study specifically focused on senior residents in nursing homes who fell into the same age group.


So what were some methods used in this study? For Covid testing, a method called polymerase chain reaction(PCR) was used where the genetic material of the patient was tested to see if there were any viral strains in it. If the Covid DNA strands replicated, the test would be considered positive(viruses have to mutate or make multiple copies of themselves to survive) and if it didn’t , the test would be considered negative. In other words, the presence of viral genetic material confirms if a patient has Covid-19.


Another method called antigen testing was also used where tests identify Covid-19 antigens in the patients sample. Antigens are viral proteins that if detected would result in a positive test.


Residents were tested every 3-7 days and assessed daily for symptoms. Residents were deemed symptomatic if symptoms appeared 5 days prior to or 14 days after the test. This is a safety window to allow researchers to account for anything that the test itself cannot.


Incidence Cases vs Vaccination Status

Figure 1. Adapted from White et. al (2021).

As you can see from the table, there were two treatment groups and one control group. Between the two treatment groups, one group received at least one dose while the other received both doses. The control, or unvaccinated, group served as a baseline for the vaccine’s effect on the experimental groups.


Participants from all three groups were tested every 3-7 days for infection and all three groups had a significant number of positive cases in the first two week period, which decreased over time. The good thing is that less than 10% of cases in each group came out positive for Covid-19. More than 90% of the cases were negative. At first it might seem surprising that within the first two weeks(0-14 day period), both Group 2(fully vaccinated) and Group 3(unvaccinated) had almost the same number of cases while Group 1(one dose) had more cases than either, but try comparing the number of people that got vaccinated to the number of people that didn’t. The number of people vaccinated with at least one dose undoubtedly outnumber the unvaccinated group. So naturally the ratio of positive cases between the experimental and control group is higher. However, perhaps even more intriguing is the effect of vaccination in the following weeks. Within 2-4 weeks, incidence cases in the unvaccinated group dropped from 173(recorded during the 0-14 day period) to 69(15-28 day period). And although it is hard to conclude how much vaccination really affected the control group, it can safely be said that it had a notable influence on the decline in cases in both vaccinated groups.


Also, within the number of cases, both the number of asymptomatic and symptomatic cases recorded in the 0-14 day period declined by 50% or more in the following weeks as the vaccines reached their full potency. However, it is important to note that the ratio of asymptomatic to symptomatic cases was still significantly higher across all three groups; more than 50% of infection cases in each group were asymptomatic. In other words, the number of infected people that didn’t show symptoms outnumbered the people that did, so there is a higher risk of transmitting the virus.


Interestingly enough, the unvaccinated group demonstrated a consistent decrease in infection rates after widespread vaccination, even though they received no treatment. Along with successfully demonstrating the effectiveness of vaccines, this study proves that with the right safety measures, it is possible to overcome this disease.


Decrease in cases show effectiveness of vaccines and additional cases seen in even vaccinated residents show there is a need for more vaccination and testing programs to avoid future outbreaks.


The results of this study have made it very clear that vaccines are the key to win the battle against this deadly virus. It has proven the real-world effectiveness of these vaccines and how with the right measures, can be used to protect even the most vulnerable populations of the nation. The effect of robust vaccine coverage can be so powerful that even small groups of unvaccinated people will be protected from the virus to some extent. However, we must remind ourselves that for all this to work, more people need to get vaccinated and tested regularly, or else the virus will continue to look for new hosts.


by Rida Khan


Works Cited:


White, E. M., Yang, X., Blackman, C., Feifer, R. A., Gravenstein, S., & Mor, V. (2021). Incident SARS-CoV-2 Infection among mRNA-Vaccinated and Unvaccinated Nursing Home Residents. New England Journal of Medicine, 385(5), 474-476. doi:10.105gfv6/nejmc2104849



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