Can people vaccinated against COVID-19 still spread the coronavirus? –

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Can people vaccinated against COVID-19 still spread the coronavirus? – fr


To take away:

  • Vaccines can be great for keeping you from getting sick, while not necessarily preventing you from getting infected or spreading the germ.
  • Preliminary evidence seems to suggest that COVID-19 vaccines reduce the likelihood that a vaccinated person will transmit the coronavirus, but the evidence is not yet flawless.
  • Unvaccinated people should always be diligent about wearing masks, physical distancing, and other coronavirus precautions.

When the United States Centers for Disease Control and Prevention changed their mask-wearing guidelines on May 13, 2021, many Americans were a little confused. Now anyone who is fully vaccinated can participate in indoor and outdoor activities, large or small, without wearing a mask or physically distancing.

Anthony Fauci, chief medical adviser to President Biden, said the new directive is “based on developments in science” and “serves as an incentive” for nearly two-thirds of Americans who are not yet fully vaccinated to go ahead and get vaccinated. the shot.

But some people cannot be vaccinated due to underlying conditions. Others with weakened immune systems, due to cancer or medical treatments, may not be fully protected by their vaccinations. Children aged 12 to 15 only became eligible for the Pfizer-BioNTech vaccine on May 10, 2021. And no COVID-19 vaccine is yet authorized for nearly 50 million children in the United States under the age of 12. years.

As the restrictions are lifted and people start leaving their masks at home, some people are concerned: Can you catch COVID-19 from a vaccinated person?

Vaccines do not always prevent infection

Researchers had hoped to design safe COVID-19 vaccines that would prevent at least half of those vaccinated from having symptoms of COVID-19.

Fortunately, the vaccines have far exceeded expectations. For example, in 6.5 million people in Israel, aged 16 and over, the Pfizer vaccine – BioNTech mRNA COVID-19 was found to be 95.3% effective after the two injections. In two months, among the 4.7 million fully vaccinated people, detectable infections increased 30-fold. Similarly in California and Texas, only 0.05% of fully vaccinated health workers tested positive for COVID -19.

Vaccine developers often hope that in addition to preventing disease, their vaccines will achieve “sterilizing immunity,” where the vaccination even prevents the germ from entering the body. This sterilizing immunity means that a vaccinated person will not catch the virus or transmit it further. However, for a vaccine to be effective, it does not have to stop the germ from infecting an immune person.

Salk’s inactivated polio vaccine, for example, does not completely prevent the polio virus from growing in the human gut. But it’s extremely effective in preventing crippling disease because it triggers antibodies that prevent the virus from infecting the brain and spinal cord. Good vaccines provide effective and long-lasting training for the body’s immune system, so when it actually encounters the pathogen causing the disease, it is ready to mount an optimal response.

When it comes to COVID-19, immunologists are still figuring out what they call “correlates of protection,” factors that predict how protected a person is from the coronavirus. Researchers believe that an optimal amount of “neutralizing antibodies,” the type that not only bind the virus but also prevent it from infecting, are enough to ward off repeated infections. Scientists are also still evaluating the durability of the immunity that COVID-19 vaccines provide and where in the body they work.

Vaccination can mean far fewer infections, but it is not certain that it will stop transmission from those who are vaccinated.
Ethan Miller / Getty Images News

Can a vaccinated person spread coronavirus?

Immunologists expect vaccines that protect against viral diseases also reduce the transmission of the virus after vaccination. But it is actually difficult to determine for sure whether people who have been vaccinated are not spreading the germ.

COVID-19 poses a particular challenge because people with asymptomatic and pre-symptomatic infections can spread the disease – and insufficient contact tracing and testing means people without symptoms are rarely detected. Some scientists estimate that the number of asymptomatic COVID-19 infections in the general population could be 3 to 20 times higher than the number of confirmed cases. Research suggests that undocumented cases of COVID-19 in people who are asymptomatic or with very mild illness could be responsible for up to 86% of all infections, although other studies contradict the high estimates.

In one study, the CDC tested volunteer healthcare workers and other frontline workers at eight U.S. sites for SARS-CoV-2 infections every week for three months, regardless of symptoms or vaccination status. Researchers found that fully immunized participants were 25 times less likely to test positive for COVID-19 than those who were not vaccinated. Findings like this imply that while vaccinated people are so well protected against infection, they are also unlikely to spread the virus. But without contact tracing to track transmission in a larger population, it is impossible to know if the hypothesis is true.

What we do know for sure is that if someone becomes ill with COVID-19 after vaccination, in what is called a “rupture infection”, the symptoms will be milder. Studies have shown that people who tested positive for COVID-19 after receiving just their first dose of the vaccine had lower levels of the virus in their bodies than unvaccinated people who tested positive. Researchers believe the decrease in viral load suggests that vaccinated people who contract the virus will be less infectious because they will have far fewer viruses that could spread to others.

A preprinted study that has not yet been peer reviewed suggests that the Moderna mRNA COVID-19 vaccine may produce anti-coronavirus antibodies in oral and nasal fluid. Since this is where SARS-CoV-2 enters, antibodies in the mouth and nose should prevent the virus from entering the body, effectively providing “sterilizing immunity”. It would also mean that vaccinated people would likely not spread the virus through respiratory droplets.

This evidence is promising. But without more studies, scientists cannot yet conclude that COVID-19 vaccines really protect against all transmission. Studies attempting to answer this question directly with contact tracing are only just beginning: Researchers will be tracking COVID-19 infections among vaccinated and unvaccinated volunteers and their close contacts.

CDC guidelines still ask those who are not yet vaccinated to mask themselves and maintain their physical distance.
Educational Pictures / Universal Pictures Group via Getty Images

Protection and prevention go hand in hand

Vaccines help slow the spread of an infectious disease by breaking the chain of infection. Those who are infected eventually have fewer and fewer unprotected people to pass the virus to. This is how a vaccine increases the immunity of the herd – susceptible and not yet immunized people are surrounded by a “herd” of people who have become immune, either through vaccination or a previous infection. But studies suggest that, for a combination of biological and social reasons, vaccination alone is unlikely to confer herd immunity against COVID-19 and completely contain the coronavirus.

In fact, vaccination alone can take a long time to eradicate a disease. Even diseases that are almost “wiped out” – like chickenpox, measles and pertussis – can resurface with waning immunity and declining vaccination rates.

The recent outbreak of infections among vaccinated New York Yankees shows that vaccinated people can not only be infected, but also transmit the coronavirus to close contacts. Highly tested groups, such as professional sports teams, point out that mild and asymptomatic infections among vaccinees in the general population may in fact be more common than reported. A similar outbreak among airport workers in Singapore shows that even among fully vaccinated variants, newer, more infectious variants can spread quickly.

The CDC’s relaxed guidelines on masking are intended to reassure those vaccinated that they are safe from serious illness. And they are. But the picture is less clear to the unvaccinated who interact with them. Until near collective immunity to COVID-19 is achieved and clear evidence accumulates that vaccinated people do not spread the virus, I and many epidemiologists believe it is best to avoid situations where there are chances of getting infected. Vaccination, coupled with continued masking and social distancing, is always an effective way to stay safer.

[The Conversation’s most important coronavirus headlines, weekly in a science newsletter]

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