< Vaccines
Can I pass on the COVID-19 if I am vaccinated?
Text updated on 2021-09-07
Yes, it is possible if you have had prior contact with an infected person, but the risk seems low!
A vaccinated person cannot get COVID just with the vaccine, because the vaccine cannot induce the production of infectious virus particles in the vaccinated person. This is because the virus, in order to be infectious, must be made up of several elements (its genetic material, specific proteins attached to the genetic material, a lipid membrane, various membrane proteins including the spike protein). However, in the Pfizer, Moderna, Astrazeneca, Janssen and Sputnik vaccines, there is only one element (the spike protein) and this element is not sufficient to trigger the production of infectious virus particles in the vaccinated person. See the question What are the different types of vaccines against COVID-19 ?.
A vaccinated person can be infected with SARS-CoV-2 if they have close contact with an infected person. See the question What is the risk of getting COVID-19 for a vaccinated person? Studies show that in populations where large numbers of people are vaccinated, the risk of getting COVID-19 for unvaccinated people is lower than in populations with low vaccination rates. This suggests that if vaccinated people get COVID-19they are less infectious. Why is this? In vaccinated people who are subsequently infected with the coronavirus SARS-CoV-2, the viral load, i.e. the amount of virus in the body, is lower than in those who are not vaccinated. One explanation is that the risk of contagion is correlated with the viral load: the lower the viral load, the lower the risk of contagion. In conclusion, vaccinated people not only have a low risk of getting COVID-19but they also have a lower risk of transmitting COVID-19. Since the risk of transmission still exists in vaccinated people, and since the new variants of the coronavirus that appear are generally more transmissible than the old ones, it is preferable to wear a mask in places with a high risk of contamination (closed places with many people), even if you are vaccinated.
Sources
Regularly updated compilation of vaccine effectiveness COVID. Vaccine effectiveness is measured in several ways: (1) prevention of infection, i.e. the effectiveness of the vaccine in stopping transmission of the virus from one person to another. An exposed person will not contract the virus, nor, by definition, develop symptoms or disease; (2) prevention of asymptomatic disease: the vaccine's effectiveness in preventing an exposed person who has contracted the virus from developing symptoms; (3) prevention of symptomatic disease: the vaccine's effectiveness in preventing an exposed individual from suffering symptoms following infection COVID-19(3) prevention of severe disease and death: the effectiveness of the vaccine in preventing an exposed individual from developing severe symptoms that often require hospitalization and lead to death.
IHME (2021) COVID-19 vaccine efficacy summary.This study of a cohort of 552,984 index cases (persons infected with SARS-CoV-2) and 1,449,427 contact cases shows that the risk of transmission of COVID-19 is reduced by 40-50% in index cases who received a first injection of vaccine (Pfizer or AstraZeneca) at least 21 days before acquiring COVID-19.
Harris, R. J., Hall, J. A., Zaidi, A., Andrews, N. J., Dunbar, J. K., & Dabrera, G. (2021). Impact of vaccination on household transmission of SARS-COV-2 in England. medRxiv.This study shows that the higher the vaccination rate in the population (vaccinated here with the Pfizer vaccine), the lower the risk of catching COVID-19 for unvaccinated people decreases. High vaccination rates are associated with lower infection rates in the unvaccinated.
Milman, O., Yelin, I., Aharony, N. et al. Community-level evidence for SARS-CoV-2 vaccine protection of unvaccinated individuals. Nat Med (2021).This study shows that in people who are infected with SARS-CoV-2 after being vaccinated, the viral load is lower than in non-vaccinated people. The reduction in viral load will decrease the shedding of virus particles and may therefore have an effect on infectivity.
Levine-Tiefenbrun, M., Yelin, I., Katz, R. et al. Initial report of decreased SARS-CoV-2 viral load after inoculation with the BNT162b2 vaccine. Nat Med 27, 790-792 (2021).Modelling study showing that the risk of transmission of COVID-19 from a vaccinated person is 12 times lower than from an unvaccinated person.
Bosetti, P., Kiem, C. T., Andronico, A., Colizza, V., Yazdanpanah, Y., Fontanet, A., ... & Cauchemez, S. (2021). Epidemiology and control of SARS-CoV-2 epidemics in partially vaccinated populations: a modeling study applied to France.Summary of the efficacy of different vaccines in relation to different variants of the coronavirus SARS-CoV-2.
Korsia-Meffre, S. (2021) Variants of SARS-CoV-2 : how effective are real-life vaccines? Vidal.fr.