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The conversation
Can vaccinated people still spread the coronavirus?
People who have been vaccinated wonder if they can facilitate social distancing and wearing a mask. AP Photo / Darko BandicEditor’s note: So you received your coronavirus vaccine, waited two weeks for your immune system to respond to the shot and you are now fully vaccinated. Does that mean you can make your way around the world like the good old days without worrying about spreading the virus? Deborah Fuller is a microbiologist at the University of Washington and works on coronavirus vaccines. She explains what science shows about post-vaccination transmission – and whether new variants might change that equation. 1. Does vaccination completely prevent infection? The short answer is no. You can still get infected after being vaccinated. But your chances of getting seriously ill are almost zero. Many people think that vaccines work like a shield, completely preventing a virus from infecting cells. But in most cases, a person who is vaccinated is protected against disease, not necessarily infection. Every person’s immune system is a little different, so when a vaccine is 95% effective, it just means that 95% of people who get the vaccine will not get sick. These people could be completely protected from infection, or they could be infected but remain asymptomatic because their immune system clears the virus very quickly. The remaining 5% of people vaccinated can become infected and get sick, but they are extremely unlikely to be hospitalized. Vaccination doesn’t 100% prevent you from getting infected, but in any case, it gives your immune system a head start on the coronavirus. Whatever your outcome – whether it’s full protection against infection or a certain level of illness – you’ll be better off after encountering the virus than if you weren’t vaccinated. Vaccines prevent disease, not infection. 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 risk of that happening. In general, if the vaccination doesn’t completely prevent infection, it will significantly reduce the amount of virus coming out of your nose and mouth – a process called shedding – and shorten the time you expel the virus. This is a big deal. A person who spreads less virus is less likely to pass it on to someone else. This appears to be the case with coronavirus vaccines. In a recent pre-print study that has not yet been peer-reviewed, Israeli researchers tested 2,897 vaccinated people for signs of coronavirus infection. Most had no detectable virus, but those infected had a quarter of the amount of virus in their bodies than unvaccinated people tested at similar times after infection. Less coronavirus virus means less chance of spreading it, and if the amount of the virus in your body is low enough, the likelihood of transmitting it can be almost zero. However, researchers do not yet know where this threshold is for the coronavirus, and since vaccines do not offer 100% protection against infection, the Centers for Disease Control and Prevention recommends that people continue to wear them. masks and social distancing even after having been vaccinated. New, more infectious and transmissible variants of the coronavirus could limit the effectiveness of current vaccines. AP Photo / John Raoux 3. What about new coronavirus variants? New variants of the coronavirus have appeared 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 gets new mutations. In recent months, researchers have discovered new, more infectious variants – meaning a person has to breathe less virus to become infected – and other variants that are more transmissible – meaning they increase the amount of virus that a person sheds. And researchers have also found at least one new variant that appears to be better at evading the immune system, according to initial data. So how does this relate to vaccines and transmission? For the South African variant, the vaccines still offer greater than 85% protection against the severe illness of COVID-19. But when you count the mild and moderate cases, they only offer around 50% to 60% protection at best. This means that at least 40% of those vaccinated will still have an infection that is strong enough – and enough virus in their body – to cause at least moderate illness. If vaccinated people have more virus in their body and it takes less to infect another person, the likelihood that a vaccinated person can transmit these new strains of the coronavirus will be higher. If all goes well, vaccines will very soon reduce the rate of serious illness and death around the world. Of course, any vaccine that reduces the severity of the disease also reduces, at the population level, the amount of virus shed as a whole. 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 will likely take much longer for vaccines to reduce transmission and for populations to achieve herd immunity than if these new variants had never emerged. The exact time it will take is balancing the effectiveness of vaccines against emerging strains and the degree of transmission and infection of these new strains. [Research into coronavirus and other news from science Subscribe to The Conversation’s new science newsletter.]This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Deborah Fuller, University of Washington. Learn more: How to stay safe with a new variant of the rapidly spreading coronavirus at large What you need to know about the new variants of COVID-19 Deborah Fuller receives funding from the National Institute of Health and Defense Threat Reduction Agency.
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