As new variants continue to surge (check this post for more information), the growing number of stories mentioning vaccinated people getting COVID are raising concerns. While it may seem that the presence of these cases negates the importance of the vaccine, this is not the case. On the surface, the anti-vax rhetoric surrounding these cases may seem somewhat reasonable; if vaccinated people can still get the virus*, why are we mandating vaccines?
The answer lies in the frequency and severity of cases. People who are vaccinated are much less likely to develop COVID-19 or have severe symptoms and require hospitalization [1,2]. No vaccine is perfect at preventing a virus from making its way into your body; instead, it prepares your immune system to fight the virus, keeping you from getting very sick if your body ever has to mount a defense against the intruder. Check out this post for more information.
Many hospitalizations happen for those that are unvaccinated or have only one dose. For instance, when the Delta variant was rising during the first week of November in Quebec, 333 of the 545 new COVID-19 cases were in those that were fully unvaccinated, and 19 people who only had one dose [3]. This shows that unvaccinated people are at a higher risk of getting COVID-19 than those vaccinated.
Most of the cases where vaccinated people are getting infected with the virus are due to the amount of exposure. For example, health care workers are constantly working with COVID-19 patients, they are being exposed to higher amounts of the virus, and this puts them at greater risk [7]. This is also creating a shortage of hospital personnel, and it’s the reason we need to continue following measures like social distance.
Another reason for these cases in vaccinated people is the way our adaptive immune responses naturally decrease over time. For instance, there was an above 90% immunity provided by both doses of Pfizer and Moderna and around 72% for the single J&J jab, though some studies have shown that after 4 months that value of protection potentially drops from 91% to 77% in Pfizer [4]. Most importantly, most studies show protection of above 95% against significant illness and death in all these vaccines. In immunocompromised people, like the elderly, people with HIV, or people who are on immunosuppressants, these values may be lower, which may account for many of the cases leading to hospitalizations in people who are fully vaccinated.
These reductions in protection highlight the reason some people have begun receiving third doses (more information here). As the immune response dampens over time, it is crucial to remind the intruder it may need to fend off in the future. Since those with weakened immune systems face an even steeper drop-off in protection than the general population values, they are prioritized for boosters.
While vaccine shortages worldwide have led to hesitations in governments allowing boosters, the U.S. has approved boosters for Moderna or Pfizer after 6 months of full immunity, and a booster for the single-jab J&J virus after two months [5]. Canada announced on November 9th that boosters will be available for those who have been fully vaccinated more than six months ago, prioritizing the elderly and individuals who have received AstraZeneca or Covishield [6]. This push for boosters is warranted as a need to maintain the population’s high immunity to the virus and halt future waves.
The vaccine, even if imperfect, is also crucial for curbing the spread of the highly contagious variants. The effectiveness values for Pfizer, Moderna, and J&J against the Delta variant indicate that these vaccines are crucial in curbing the spread of this strain [3,8]. In nursing home patients, the effectiveness drops to around 53% for the Delta variant, highlighting yet again why boosters are important, and why everyone benefits when people around them are vaccinated [9].
The recently-discovered Omicron variant is another reason why there are positive cases in vaccinated people. The CDC has reported that vaccines are likely protecting against the most severe outcomes (including hospitalization and death) [10]. Considering that Omicron cases are found even in fully vaccinated people, the need for boosters has been highlighted. Stay tuned for future posts where we will delve into the new findings regarding Omicron!
With over a year and a half into the pandemic, everyone is itching to return to a virus-free normal. It remains that vaccines, even if they do not provide 100% protection, are highly effective in preventing severe COVID-19, hospitalization, death, and curbing the spread of the virus from person to person.
*Virus - it can be considered a very small and basic life form or an aggregate of molecules that is simpler than a cell. They can be found in the environment or inside living organisms. It has to infect a cell and use its machinery to multiply, since it cannot multiply by itself. Viruses consist of nucleic acids (DNA or RNA), a protein capsid that contains the nucleic acids and, sometimes, an external envelope of lipids. The flu, measles, AIDS and Covid-19, for instance, are caused by viruses.
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Written by: Dominique
Edited by: María, Natasha, and Nicole
BioDecoded is a volunteer group committed to sharing accurate scientific information. We cannot offer any specific health advice. If you have any doubts about getting vaccinated due to previous health conditions, please speak with your healthcare professional or family physician. Your doctor can revise your medical history and advise you on the best path to follow. If you have any questions about this topic, please comment or send them to our email.
References:
Why are we seeing more COVID cases in fully vaccinated people? An expert explains. The Conversation (2021). Available at: https://theconversation.com/why-are-we-seeing-more-covid-cases-in-fully-vaccinated-people-an-expert-explains-166741 (Accessed: 18th November 2021)
Breakthrough infections might not be a big transmission risk. Here’s the evidence. NPR (2021) Available at: https://www.npr.org/sections/health-shots/2021/10/12/1044553048/covid-data-vaccines-breakthrough-infections-transmission (Accessed: 18th November 2021)
Quebec reports 545 new COVID-19 cases, 352 of those not fully vaccinated. CTV News (2021). Available at: https://montreal.ctvnews.ca/quebec-reports-545-new-covid-19-cases-352-of-those-not-fully-vaccinated-1.5655759 (Accessed: 18th November 2021)
Comparing the COVID-19 Vaccines: How are they different? Yale Medicine (2021). Available at: https://www.yalemedicine.org/news/covid-19-vaccine-comparison (Accessed: 18th November 2021)
COVID-19 Vaccine Booster Shots. CDC (2021). Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/booster-shot.html (Accessed: 18th November 2021).
Health Canada authorizes the use of the Pfizer-BioNTech Comirnaty COVID-19 vaccine as a booster shot. Health Canada (2021). Available at: https://www.canada.ca/en/health-canada/news/2021/11/health-canada-authorizes-the-use-of-the-pfizer-biontech-comirnaty-covid-19-vaccine-as-a-booster-shot.html (Accessed: 18th November 2021)
Jung J, Sung H, Kim SH. Covid-19 Breakthrough Infections in Vaccinated Health Care Workers. N Engl J Med. 2021;385(17):1629-1630. doi:10.1056/NEJMc2113497. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa2109072
Nasreen, S. et al. Effectiveness of mRNA and ChAdOx1 COVID-19 vaccines against symptomatic SARS-CoV-2 infection and severe outcomes with variants of concern in Ontario. (2021). Available at: https://www.medrxiv.org/content/10.1101/2021.06.28.21259420v1.full.pdf
Nanduri S, Pilishvili T, Derado G, et al. Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August 1, 2021. MMWR Morb Mortal Wkly Rep 2021;70:1163-1166. Available at: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e3.htm
Omicron Variant: What You Need to Know. CDC (2021): Available at: https://www.cdc.gov/coronavirus/2019-ncov/variants/omicron-variant.html (Accessed: 30th December 2021)
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