On December 18, the US Food and Drug Administration granted the emergency use authorization for Moderna’s COVID-19 vaccine. The vaccine is the second to be approved in the United States, and the first doses were administered on Monday.
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It is not yet clear whether the COVID-19 vaccines will prevent vaccinated people from transporting the new coronavirus without feeling ill and without inadvertently spreading it. It is still important for vaccinated individuals to mask themselves.
This milestone is impressive because the Moderna and Pfizer vaccines were developed at record speed and because they appear to be more than 90 percent effective (at least in clinical trials) in protecting people against the development of symptomatic COVID-19. But one thing that remains unclear is whether the COVID-19 vaccines will also prevent vaccinated people from carrying the new coronavirus without feeling bad and without spreading it to others. This means that, for now, it is important to continue wearing masks, distancing yourself socially and taking other precautionary measures, even if you have been vaccinated.
“It wouldn’t be so far-fetched to have a vaccine that protects you from developing the worst COVID disease, but you could be infected and spread it [without] getting very sick, ”says Jeffrey Bethony, professor of microbiology, immunology and tropical medicine at George Washington University School of Medicine and Health Sciences who works with vaccines for parasitic diseases and HIV. “There is hope that they will avoid transmission, but we just don’t know enough about them yet.”
One of the reasons this new virus – officially called SARS-CoV-2 – has spread so intensely is that people can be contagious for several days before feeling bad and, in some cases, never develop symptoms. This high rate of asymptomatic spread “is not so common in other infections,” says Susanna Naggie, associate professor of medicine at Duke University School of Medicine, specializing in infectious diseases. “With the flu, there is asymptomatic disease, but not at the level we see with SARS-CoV-2.” This makes it particularly important to understand whether COVID-19 vaccines will prevent asymptomatic infections, she says.
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It is not yet clear whether the COVID-19 vaccines will prevent vaccinated people from transporting the new coronavirus without feeling ill and without inadvertently spreading it. It is still important for vaccinated individuals to mask themselves.
Many vaccines – including those for hepatitis A and B, measles, chicken pox and human papillomavirus – prevent people from getting sick and transmitting the pathogen to others. “We generally believe that if you have a vaccine that prevents disease, you are probably also preventing infections, but you cannot assume that this is 100 percent [the case]”Says Naggie.
Some pathogens can infect and reproduce in people vaccinated for short periods of time without making them sick, including the bacteria that cause meningitis and whooping cough or whooping cough. This is also a problem for vaccines under development for parasitic diseases like malaria, schistosomiasis and hookworm infection, says Bethony. “The vaccine protects people against the most serious clinical manifestations of the disease, but it does not completely stop the infection,” says Bethony. “You can still have a person who is slightly infected and is still able to spread the disease.”
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Whether an inoculation will prevent infection depends in part on the vaccine’s mechanism of action. Many COVID-19 vaccines, including those from Moderna and Pfizer, target thorn-shaped proteins on the surface of SARS-CoV-2 that help it bind and enter host cells. “We are talking about the development of antibodies and an immune response directly to the protein spike,” says Naggie. “So the hope is that you can actually prevent the infection.”
Several developers have reported initial data suggesting that their COVID-19 vaccines will reduce asymptomatic infections. During the final stage tests of the vaccine developed by the University of Oxford and AstraZeneca, some participants received weekly COVID-19 tests. One group accidentally received a first low dose of the vaccine followed by the second desired total dose. Asymptomatic infections were less common in this vaccinated group than among those who received a placebo. The researchers are still investigating why that low-dose group did better than the full-dose group in that regard.
In Moderna’s clinical trials, the researchers cleaned the participants before receiving each of the two doses of the vaccine. On December 15, the drugmaker reported that 38 volunteers who received the placebo tested positive without showing symptoms of COVID-19 before the second dose, compared with just 14 in the group that received the vaccine.
“Presumably, this means that it also reduces the risk of transmission, although to prove it will require a lot more work,” says Naggie. “Maybe the vaccine completely prevents the infection, or maybe it really shortens the infection period and someone expands by just a few days … all of these would be very critical pieces to answer that.”
Investigating this issue may become easier as domestic COVID-19 test kits become more common. In follow-up clinical tests, researchers can ask people to clean themselves daily and track how often vaccinated people are positive and whether they transmit the virus to other members of their household, says Naggie.
Several vaccine developers, including Moderna and Pfizer, are planning to test the blood of the trial participants for antibodies that recognize a part of the virus that was not the target of the vaccine. These antibodies would indicate whether a person was infected after being vaccinated.
Another way to find out how well COVID-19 vaccines prevent transmission is to monitor areas where vaccination is prevalent to see if infections also fall among the remaining unvaccinated people, says Bethony. This type of situation occurred after the introduction of the first polio vaccine in 1955; the following year, scientists saw even fewer cases than they expected, because a sufficient number of children had been immunized and the virus had trouble reaching those who did not.
In the United States, COVID-19 vaccines have only become available in recent weeks and are not expected to be distributed to the general public before next spring. It will be a while before we reach the herd’s immunity. It is also unclear what percentage of Americans need to be vaccinated to reach this stage, as collective immunity depends on many factors, including how quickly the virus spreads in various communities and the effectiveness of vaccines in preventing the spread of the virus. new virus.
“We are only having access to the vaccine, and so for a few months … we are probably still examining questions about the vaccine’s role in transmission and the need to continue all these public health measures,” says Naggie. “For now, until we have adequate immunity in our communities and until we know better about transmission, the answer is yes.” So get vaccinated when you can and keep on masking yourself.
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