- As vaccination against COVID-19 continues around the world, many people are still unclear about what vaccines mean for transmission.
- Deborah Fuller, a microbiologist, answers three questions about transmission after the vaccine and whether new variants could affect it.
- Vaccination does not 100% prevent you from becoming infected, but it does reduce the chances of getting it or falling seriously.
- If a vaccinated person catches COVID-19, the chances of transmitting it are lower, due to the reduction in the viral load that can be transmitted.
So you’ve got the coronavirus vaccine, waited two weeks for your immune system to respond to the shot, and now you’re completely vaccinated. Does that mean you can make your way around the world like the old days without fear of spreading the virus? Deborah Fuller is a microbiologist at the University of Washington School of Medicine who works on coronavirus vaccines. She explains what science shows about transmission after vaccination and whether new variants could change that equation.
1. Does vaccination completely prevent infection?
The short answer is no. You can still get infected after getting vaccinated. But your chances of getting seriously ill are almost nil.
Many people think that vaccines work like a shield and prevent a virus from completely infecting cells. But in most cases, a person who is vaccinated is protected from disease, not necessarily from infection.
Each person’s immune system is a little different, so when a vaccine is 95% effective, it just means that 95% of people who get it won’t get sick. These people may be completely protected from infection or become infected, but they would remain asymptomatic because their immune system clears the virus very quickly. The remaining 5% of vaccinated people can become infected and ill, but are very unlikely to be admitted.
Vaccination does not 100% prevent you from becoming infected, but in all cases, it gives your immune system a big influence on the coronavirus. Whatever your outcome, whether it’s complete protection against infection or some level of illness, you’ll be better off after encountering the virus than if you hadn’t been vaccinated.
Vaccines prevent disease and not infection.
Image: National Institute of Allergies and Infectious Diseases, CC BY
2. Does infection always mean transmission?
Transmission occurs when there are enough viral particles from an infected person in the body of an uninfected person. In theory, anyone infected with the coronavirus could transmit it. But a vaccine will reduce the chances of this happening.
In general, if vaccination does not completely prevent the infection, it will significantly reduce the amount of virus coming out of the nose and mouth (a process called shedding) and shorten the time you go around the virus. This is a great thing. A person who emits fewer viruses is less likely to transmit it to another person.
This appears to be the case for coronavirus vaccines. In a recent prepress study that has not yet been peer-reviewed, Israeli researchers tested 2,897 people vaccinated to detect signs of coronavirus infection. Most had no detectable viruses, but infected people had a quarter of the amount of virus in the body, as unvaccinated people tested at similar times after infection.
Less coronavirus virus means less chance of spreading it and, if the amount of virus in the body is low enough, the probability of transmitting it can reach almost zero. However, researchers still do not know where this limit for coronavirus is, and since vaccines do not offer 100% protection against infection, the Centers for Disease Control and Prevention recommends that people continue to use masks and distance. social even after I have been vaccinated.
New variants of the coronary virus, more infectious and transmissible, may limit the effectiveness of current vaccines.
Image: AP Photo / John Raoux
3. What about the new variants of the coronavirus?
New coronavirus variants have emerged in recent months and recent studies show that vaccines are less effective against certain ones, such as variant B1351 first identified in South Africa.
Each time SARS-CoV-2 is reproduced, it gets new mutations. In recent months, researchers have found new variants that are more infectious, meaning that a person needs to breathe less virus to become infected, and other variants that are more transmissible, that is, increase the amount of virus that throws a person. And researchers have also found at least one new variant that appears to be better for eluting the immune system, according to early data.
So how does this relate to vaccines and transmission?
For the South African variant, vaccines still offer over 85% protection against serious disease with COVID-19. But when mild to moderate cases are counted, they provide, at best, only 50% -60% protection. This means that at least 40% of vaccinated people will still have an infection strong enough (and enough virus in the body) to cause at least moderate illness.
If vaccinated people have more viruses in their bodies and fewer viruses are needed to infect another person, a vaccinated person will be more likely to be able to transmit these new strains of the coronavirus.
If all goes well, vaccines will soon reduce the rate of serious illness and death worldwide. Of course, any vaccine that reduces the severity of the disease also reduces, at the population level, the amount of virus that is released in general. But due to the emergence of new variants, vaccinated people still have the potential to spread and spread the coronavirus to other people, vaccinated or not. This means that it is likely to take much longer to reduce the transmission of vaccines and get the population to reach herd immunity than if these new variants had never appeared. The time it will take is exactly a balance between the effectiveness of vaccines against emerging strains and the transmission and infection of these new strains.