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Can vaccinated people still spread the coronavirus?



** For local vaccine history, see below.

Those who have received the coronavirus vaccine and waited two weeks for their immune system to respond are officially fully vaccinated.

The actual test of Pfizer’s COVID-19 vaccine in more than half a million people confirms that it is very effective in preventing serious illness or death, even after a single dose.

But does this mean that vaccinated people cannot carry and spread the virus?

Deborah Fuller is a microbiologist at the University of Washington who works on coronavirus vaccines. She explains what science shows about post-vaccination transmission ̵

1; and whether new options can change that equation.

Does vaccination mean complete prevention?

The short answer is no. You can still become infected after you have been vaccinated. But your chances of getting sick are almost zero.

Many people believe that vaccines act as a shield, blocking the virus from completely infecting cells. But in most cases, a person who is vaccinated is protected from disease, not necessarily from infection.

Everyone’s immune system is a little different, so when the vaccine is 95% effective, it just means that 95% of the people who get the vaccine will not get sick. These people can be completely protected from infection or become infected, but remain asymptomatic, as their immune system eliminates the virus very quickly. The remaining 5% of those vaccinated can become infected and get sick, but are very unlikely to be hospitalized.

Vaccination does not protect you 100% from infection, but in any case it gives your immune system a leg up from the coronavirus. Whatever your outcome – whether it is complete protection against infection or some level of disease – you will be better off after being exposed to the virus than if you have not been vaccinated.

Does infection always mean transmission?

Transmission occurs when a sufficient amount of virus particles from an infected person enters the body of an uninfected person. In theory, anyone infected with the coronavirus could potentially transmit it. But the vaccine will reduce the chance of this happening.

In general, if vaccination does not completely prevent the 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 pass the virus. This is a big deal. A person who throws out less virus is less likely to pass it on to someone else.

This seems to be the case with coronavirus vaccines. In a recent prepress study that is yet to be reviewed, Israeli researchers tested 2,897 vaccinated for signs of coronavirus infection. Most did not have a detectable virus, but people who were infected had a quarter of the amount of the virus in their bodies as unvaccinated people tested at the same time after infection.

Less coronavirus virus means less chance of spreading it, and if the amount of virus in your body is low enough, the chances of transmitting it can reach almost zero. However, researchers still do not know where this restriction is for coronavirus, and because vaccines do not provide 100% protection against infection, the Centers for Disease Control and Prevention recommends that people continue to wear masks and social distance even after being vaccinated.

What about the new variants of the coronavirus?

New variants of the coronavirus have emerged in recent months, and recent studies have shown that vaccines are less effective against some, such as variant B1351, first identified in South Africa.

Each time SARS-CoV-2 replicates, it acquires new mutations. In recent months, researchers have discovered new variants that are more infectious – meaning that one has to inhale less virus to become infected – and other variants that are more transmissible – meaning they increase the amount of virus. which one throws away. And researchers have also found at least one new option that appears to be better at avoiding the immune system, according to early data.

So how does this relate to vaccines and transmission?

For the South African variant, vaccines still provide more than 85% protection against severe COVID-19 disease. But when counting 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 moderate disease.

If vaccinated people have more virus in their bodies and it takes less of that virus to infect another person, a vaccinated person will be more likely to transmit these new strains to 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 at the population level, reduces the amount of virus that is released in general. But due to the emergence of new variants, vaccinated people still have the potential to shed and spread the coronavirus to other people vaccinated or otherwise. This means that it is likely that it will take much longer for vaccines to reduce transmission and for populations to reach herd immunity than if these new variants never appeared. Exactly how long it will take is a balance between how effective vaccines are against emerging strains and how transmissible and contagious these new strains are.


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