In December, we launched a call for questions about COVID-19. We’ve received a number of questions and are posting the first two responses this week. The answers come from Qian (Vivian) Liu, an assistant professor at the Institute of Parasitology and a member of the Center for Viral Diseases at McGill. His research focuses on understanding virus-host interactions during infection and transmission of emerging zoonotic viruses (such as SARS-CoV-2).
1) What are the data regarding the ability of COVID-19 to spread between vaccinated individuals? How easily does it spread and how does it compare to unvaccinated people?
Liu: “Variants of concern can partially escape the protection generated by vaccination or infection and spread between vaccinated individuals. In general, variants of concern, e.g. omicron, can spread faster than parental strains of sar cov 2 wuhan-hu-1. The reason is that the variants of concern can emerge as they accumulate mutations that help them better infect cells and evade the immune response at the same time. The spread of covid between vaccinated people is slower than that of the unvaccinated. The immune response in vaccinated individuals, although sometimes compromised against variants of concern, can still provide some protection and kill some viruses during transmission.
2) There is immunity against the vaccine and natural immunity against the virus. What is the reason for insisting that people have two shots even though they have already had COVID?
Lme : “From the point of view of our immune system, the immune response generated by natural infection and vaccination is not very different. In either case, our immune system sees parts or all of the pathogen (sars cov 2 virus) and makes antibodies and other immune responses against them. In this case, the vaccine can be seen as a fake virus to trick our body into generating an immune response against the real virus. So no matter how many vaccines or natural infections the person has already had, one more can always build a stronger immune response against the virus. This has been supported by a few published clinical studies in Nature etc. early 2021, when the gamma variant was prevalent.