- As immunization with COVID-19 continues worldwide, many people still do not know what vaccines mean for transmission.
- Deborah Fuller, a microbiologist, answers three questions about post-vaccine transmission and whether new variants can affect that.
- Vaccination does not 100% prevent you from getting infected, but it does reduce the chance of getting it or getting seriously ill.
- If the vaccinee catches COVID-19, the chances of transmission are less, due to the reduction of the viral load that can be transmitted.
So you received your coronavirus vaccine, you waited two weeks for your immune system to respond to the injection and you are now fully vaccinated. Does this mean that you can roam the world as before without fear of spreading the virus? Deborah Fuller is a microbiologist at the University of Washington School of Medicine who works with coronavirus vaccines. It explains what science shows about post-vaccination transmission – and whether new variants could change that equation.
1. Does vaccination completely prevent infection?
The short answer is no. You can still become infected after being vaccinated. But your chances of getting seriously ill are almost zero.
Many people think that vaccines act as a shield, preventing a virus from completely infecting cells. But in most cases, a person who is vaccinated is protected from illness, not necessarily from infection.
Each person’s immune system is a little different, so when a vaccine is 95% effective, it means that 95% of people who get the vaccine will not get sick. These people may be completely protected from infection or they may be infected, but they remain asymptomatic because their immune system clears the virus very quickly. The remaining 5% of vaccinated people can be infected and fall ill, but it is extremely unlikely that they will be hospitalized.
Vaccination does not prevent you from being 100% infected, but in all cases it gives your immune system a great advantage over the coronavirus. Whatever your outcome – be it complete protection against infection or some level of illness – you will be better off after finding the virus than if you had not been vaccinated.
Vaccines prevent diseases, not infections.
Image: National Institute of Allergy and Infectious Diseases, CC BY
2. Does infection always mean transmission?
Transmission occurs when enough viral particles from an infected person enter the body of an uninfected person. In theory, anyone infected with the coronavirus could potentially transmit it. But a vaccine will reduce the chance of this happening.
In general, if vaccination does not completely prevent infection, it will significantly reduce the amount of virus coming out of the nose and mouth – a process called elimination – and will shorten the time it takes to clear the virus. This is a big deal. A person who spreads less viruses is less likely to pass it on to someone else.
This appears to be the case for vaccines against coronavirus. In a recent prepress study that has not yet been peer-reviewed, Israeli researchers tested 2,897 people vaccinated for signs of coronavirus infection. Most had no detectable virus, but infected people had a quarter of the amount of virus in their bodies than unvaccinated people tested at similar times after infection.
Fewer coronavirus viruses means less chance of spreading it, and if the amount of viruses in your body is low enough, the likelihood of transmitting it can reach almost zero. However, researchers still do not know where that limit is for coronavirus, and since vaccines do not provide 100% protection against infections, the Centers for Disease Control and Prevention recommend that people continue to wear masks and at a distance even after I was vaccinated.
New, more infectious and transmissible variants of the coronavirus may limit the effectiveness of current vaccines.
Image: AP Photo / John Raoux
3. What about the new variants of the coronavirus?
New variants of the coronavirus have emerged in recent months, and recent studies show that vaccines are less effective against some, such as the B1351 variant first identified in South Africa.
Each time SARS-CoV-2 replicates, it obtains new mutations. In recent months, researchers have discovered new variants that are more infectious – which means that a person needs to breathe less virus to become infected – and other variants that are more transmissible – which means that they increase the amount of virus that a person spreads. And the researchers also found at least one new variant that appears to be better for escaping the immune system, according to the first data.
So, how does this relate to vaccines and transmission?
For the South African variant, vaccines still provide more than 85% protection against serious illnesses with COVID-19. But when you count the mild and moderate cases, they provide, at best, only about 50% -60% protection. This means that at least 40% of vaccinated people will still have a strong enough infection – and enough virus in their body – to cause at least one moderate illness.
If vaccinated people have more viruses in their bodies and take less of that virus to infect another person, there is a greater likelihood that a vaccinated person will transmit these new strains of the coronavirus.
If all goes well, vaccines will soon reduce the rate of serious illness and death worldwide. To be sure, any vaccine that reduces the severity of the disease is also, at the population level, reducing the amount of virus being eliminated in general. But, due to the emergence of new variants, vaccinated people still have the potential to eliminate and spread the coronavirus to other people, vaccinated or not. This means that it will probably take much longer for vaccines to reduce transmission and populations to achieve herd immunity than if these new variants had never appeared. Exactly how long this will take is a balance between the effectiveness of vaccines against emerging strains and how transmissible and infectious these new strains are.