Lately, there are worries regarding the longevity of the COVID-19 immunization. A recent preprint study (one that has not been reviewed or officially published yet) explained that the COVID-19 vaccine’s effectiveness reaches a peak after the second dose but lowers around 5 months post-vaccination [1]. Thus, after a few months, the vaccine’s ability to prevent hospitalization and death is not as high as in the beginning of the immunization*. In the context of vaccination, this decrease in effectiveness is called “waning”. Other vaccines, like tetanus or rotavirus in children, also have some degree of waning immunity over time [2, 3].
Nevertheless, the COVID-19 vaccine is bringing durable benefits to the immune system. After the vaccine, the number of long-term memory B cells in our body continue to increase for months [4]. Therefore, even though antibody** levels decay, the immune responses induced by the vaccine continue protecting our body (please see our post and video about the immune system for more information).
Considering the new developments, some policymakers and health authorities are also proposing the use of the third dose as well as the booster dose. These two concepts are similar but not identical: A person who did not develop a full and satisfactory immune response in the first two doses is eligible to receive a third dose, so that their immune system becomes prepared to fight the virus***. In the booster dose, a person developed the full immune response after vaccination, but the immunity started decreasing and waning over time, so they are now receiving an additional shot [5,6].
Although the use of booster and third doses is recent, there is some evidence that favors the extra-dose for certain groups. In an observational study in Israel, it appears that the additional Pfizer dose may be helpful for decreasing the likelihood of infection and risk of severe disease, but the study is only analyzing a small window of time and the results could be confounded by other uncontrolled factors [7]. Scientists are working hard to understand more about the booster dose and they will continue to update the public. For the moment, the Ministry of Health in Ontario recommends that people should be adequately informed of the vaccine’s pros and cons, including the risk for pericarditis and myocarditis, among others. Both the Ministry of Health in Ontario and the CDC are accepting the use of a third dose for people who are moderately or severely immunocompromised, as well as for susceptible elderly individuals in high-risk environments [6, 8].
Ideally, if your first and second doses were Pfizer or Moderna, you should have the same vaccine for your third dose. If your first and second doses were AstraZeneca and you are not contraindicated to receive an mRNA vaccine, you should have Pfizer or Moderna as the third shot [8]. Regarding the J&J vaccine, there is not enough data yet. It is possible that people who received the J&J shot will require another J&J shot, but it is not definitive [6]. For those who are unsure about receiving a third dose or a booster shot, please contact your health care professional. It should also be noted that, depending on governmental and migratory policies, some individuals may want to take an additional shot of a certain vaccine so that their vaccination is fully recognized by the country where they are going.
For some people, the additional vaccine dose brings up mixed feelings. We want the pandemic to be over and there are more steps to cover before reaching a normal life again. Some people might even question the use of vaccines if we need boosters. Although these concerns are understandable, the use of a booster does not mean that the COVID-19 vaccines failed. Actually, vaccines continue to be very effective weapons. Like many weapons and tools, they need to be “recharged” every once in a while. It is important to remark that receiving the full vaccination schedule for COVID-19 is helping protect our body (please see the post vaccine’s efficacy against COVID-19 variants). Therefore, even putting aside the booster debate, having the first two doses is already a great idea to take care of ourselves and the people around us.
*Immunity - an established memory and quick response that our bodies have against infection by pathogens or foreign molecules that enter our bodies. When we combat and survive an infection, we normally develop resistance against the organism or molecule that caused the infection. Vaccines train our bodies to develop immunity against pathogens, without the need to be infected by them first.
**Antibody - a molecule produced by immune cells that recognizes and binds to another molecule that is foreign to the organism, the antigen. By binding to the antigen, the antibody can tag the foreign molecule for destruction or directly neutralizes it.
***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: Nicole
Edited by: María and Natasha
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:
Andrews, N., et al. Vaccine effectiveness and duration of protection of Comirnaty, Vaxzevria and Spikevax against mild and severe COVID-19 in the UK. Preprint not certified by peer review. (2021). Available at: https://khub.net/documents/135939561/338928724/Vaccine+effectiveness+and+duration+of+protection+of+covid+vaccines+against+mild+and+severe+COVID-19+in+the+UK.pdf/10dcd99c-0441-0403-dfd8-11ba2c6f5801
Domenech de Cellès, M., Rohani, P. & King, A. Duration of Immunity and Effectiveness of Diphtheria-Tetanus–Acellular Pertussis Vaccines in Children. JAMA Pediatrics 173, 588 (2019). Available at: https://jamanetwork.com/journals/jamapediatrics/fullarticle/2731128
Lopman, B. & Pitzer, V. Waxing Understanding of Waning Immunity. The Journal of Infectious Diseases 217, 851-853 (2018). Available at: https://academic.oup.com/jid/article/217/6/851/4833004
Goel, R. et al. mRNA Vaccination Induces Durable Immune Memory to SARS-CoV-2 with Continued Evolution to Variants of Concern. (2021). Available at: https://www.biorxiv.org/content/10.1101/2021.08.23.457229v1
Booster Shots and Third Doses for COVID-19 Vaccines: What You Need to Know. (2021). Available at: https://www.hopkinsmedicine.org/health/conditions-and-diseases/coronavirus/booster-shots-and-third-doses-for-covid19-vaccines-what-you-need-to-know (Accessed: 30th September 2021)
COVID-19 Vaccination. Centers for Disease Control and Prevention (2021). Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/booster-shot.html (Accessed: 30th September 2021)
Bar-On, Y. et al. Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel. New England Journal of Medicine (2021). Available at: https://www.nejm.org/doi/10.1056/NEJMoa2114255
Health.gov.on.ca (2021). Available at: https://health.gov.on.ca/en/pro/programs/publichealth/coronavirus/docs/vaccine/COVID-19_vaccine_third_dose_recommendations.pdf (Accessed: 30th September 2021)
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