The new vaccines will probably prevent you from getting sick with Covid. No one knows yet whether they will keep you from spreading the virus to others — but that information is coming.
Scientists worry that if vaccinated people are silent spreaders of the virus, they may keep it circulating in their communities, putting unvaccinated people at risk.Credit…Max Whittaker for The New York Times
- Published Dec. 8, 2020Updated Dec. 9, 2020
The new Covid-19 vaccines from Pfizer and Moderna seem to be remarkably good at preventing serious illness. But it’s unclear how well they will curb the spread of the coronavirus.
That’s because the Pfizer and Moderna trials tracked only how many vaccinated people became sick with Covid-19. That leaves open the possibility that some vaccinated people get infected without developing symptoms, and could then silently transmit the virus — especially if they come in close contact with others or stop wearing masks.
If vaccinated people are silent spreaders of the virus, they may keep it circulating in their communities, putting unvaccinated people at risk.
“A lot of people are thinking that once they get vaccinated, they’re not going to have to wear masks anymore,” said Michal Tal, an immunologist at Stanford University. “It’s really going to be critical for them to know if they have to keep wearing masks, because they could still be contagious.”
In most respiratory infections, including the new coronavirus, the nose is the main port of entry. The virus rapidly multiplies there, jolting the immune system to produce a type of antibodies that are specific to mucosa, the moist tissue lining the nose, mouth, lungs and stomach. If the same person is exposed to the virus a second time, those antibodies, as well as immune cells that remember the virus, rapidly shut down the virus in the nose before it gets a chance to take hold elsewhere in the body.
The coronavirus vaccines, in contrast, are injected deep into the muscles and stimulate the immune system to produce antibodies. This appears to be enough protection to keep the vaccinated person from getting ill.
Some of those antibodies will circulate in the blood to the nasal mucosa and stand guard there, but it’s not clear how much of the antibody pool can be mobilized, or how quickly. If the answer is not much, then viruses could bloom in the nose — and be sneezed or breathed out to infect others.
“It’s a race: It depends whether the virus can replicate faster, or the immune system can control it faster,” said Marion Pepper, an immunologist at the University of Washington in Seattle. “It’s a really important question.”
This is why mucosal vaccines, like the nasal spray FluMist or the oral polio vaccine, are better than intramuscular injections at fending off respiratory viruses, experts said.
The next generation of coronavirus vaccines may elicit immunity in the nose and the rest of the respiratory tract, where it’s most needed. Or people could get an intramuscular injection followed by a mucosal boost that produces protective antibodies in the nose and throat.
Image A mucosal spray version of the H1N1 vaccine being administered in 2009.Credit…Tannen Maury/EPA, via Shutterstock
The coronavirus vaccines have proved to be powerful shields against severe illness, but that is no guarantee of their efficacy in the nose. The lungs — the site of severe symptoms — are much more accessible to the circulating antibodies than the nose or throat, making them easier to safeguard.
“Preventing severe disease is easiest, preventing mild disease is harder, and preventing all infections is the hardest,” said Deepta Bhattacharya, an immunologist at the University of Arizona. “If it’s 95 percent effective at preventing symptomatic disease, it’s going to be something less than that in preventing all infections, for sure.”
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Answers to Your Vaccine Questions
With distribution of a coronavirus vaccine beginning in the U.S., here are answers to some questions you may be wondering about:
- If I live in the U.S., when can I get the vaccine? While the exact order of vaccine recipients may vary by state, most will likely put medical workers and residents of long-term care facilities first. If you want to understand how this decision is getting made, this article will help.
- When can I return to normal life after being vaccinated? Life will return to normal only when society as a whole gains enough protection against the coronavirus. Once countries authorize a vaccine, they’ll only be able to vaccinate a few percent of their citizens at most in the first couple months. The unvaccinated majority will still remain vulnerable to getting infected. A growing number of coronavirus vaccines are showing robust protection against becoming sick. But it’s also possible for people to spread the virus without even knowing they’re infected because they experience only mild symptoms or none at all. Scientists don’t yet know if the vaccines also block the transmission of the coronavirus. So for the time being, even vaccinated people will need to wear masks, avoid indoor crowds, and so on. Once enough people get vaccinated, it will become very difficult for the coronavirus to find vulnerable people to infect. Depending on how quickly we as a society achieve that goal, life might start approaching something like normal by the fall 2021.
- If I’ve been vaccinated, do I still need to wear a mask? Yes, but not forever. Here’s why. The coronavirus vaccines are injected deep into the muscles and stimulate the immune system to produce antibodies. This appears to be enough protection to keep the vaccinated person from getting ill. But what’s not clear is whether it’s possible for the virus to bloom in the nose — and be sneezed or breathed out to infect others — even as antibodies elsewhere in the body have mobilized to prevent the vaccinated person from getting sick. The vaccine clinical trials were designed to determine whether vaccinated people are protected from illness — not to find out whether they could still spread the coronavirus. Based on studies of flu vaccine and even patients infected with Covid-19, researchers have reason to be hopeful that vaccinated people won’t spread the virus, but more research is needed. In the meantime, everyone — even vaccinated people — will need to think of themselves as possible silent spreaders and keep wearing a mask. Read more here.
- Will it hurt? What are the side effects? The Pfizer and BioNTech vaccine is delivered as a shot in the arm, like other typical vaccines. The injection into your arm won’t feel different than any other vaccine, but the rate of short-lived side effects does appear higher than a flu shot. Tens of thousands of people have already received the vaccines, and none of them have reported any serious health problems. The side effects, which can resemble the symptoms of Covid-19, last about a day and appear more likely after the second dose. Early reports from vaccine trials suggest some people might need to take a day off from work because they feel lousy after receiving the second dose. In the Pfizer study, about half developed fatigue. Other side effects occurred in at least 25 to 33 percent of patients, sometimes more, including headaches, chills and muscle pain. While these experiences aren’t pleasant, they are a good sign that your own immune system is mounting a potent response to the vaccine that will provide long-lasting immunity.
- Will mRNA vaccines change my genes? No. The vaccines from Moderna and Pfizer use a genetic molecule to prime the immune system. That molecule, known as mRNA, is eventually destroyed by the body. The mRNA is packaged in an oily bubble that can fuse to a cell, allowing the molecule to slip in. The cell uses the mRNA to make proteins from the coronavirus, which can stimulate the immune system. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make proteins of their own. Once those proteins are made, our cells then shred the mRNA with special enzymes. The mRNA molecules our cells make can only survive a matter of minutes. The mRNA in vaccines is engineered to withstand the cell’s enzymes a bit longer, so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed.
Still, he and other experts said they were optimistic that the vaccines would suppress the virus enough even in the nose and throat to prevent immunized people from spreading it to others.
“My feeling is that once you develop some form of immunity with the vaccine, your ability to get infected will also go down,” said Akiko Iwasaki, an immunologist at Yale University. “Even if you’re infected, the level of virus that you replicate in your nose should be reduced.”
The vaccine trials have not produced data on how many vaccinated people were infected with the virus but did not have symptoms. Some hints are emerging, however.
AstraZeneca, which announced some of its trial results in November, said that volunteers had been testing themselves regularly for the virus, and that those results suggested that the vaccine might prevent some infections.
Pfizer will test a subset of its trial participants for antibodies against a viral protein called N. Because the vaccines have nothing to do with this protein, N antibodies would reveal whether the volunteers had become infected with the virus after immunization, said Jerica Pitts, a spokeswoman for the company.
Moderna also plans to analyze blood from all its participants and test for N antibodies. “It will take several weeks before we can expect to see those results,” said Colleen Hussey, a spokeswoman for Moderna.
The trials have so far analyzed only blood, but testing for antibodies in mucosa would confirm that the antibodies can travel to the nose and mouth. Dr. Tal’s team is planning to analyze matched blood and saliva samples from volunteers in the Johnson & Johnson trial to see how the two antibody levels compare.
In the meantime, Dr. Bhattacharya said, he was encouraged by recent work showing that people who received an intramuscular flu vaccine had abundant antibodies in the nose. And a study of Covid-19 patients found that antibody levels in saliva and blood were closely matched — suggesting that a strong immune response in the blood would also protect mucosal tissues.
Only people who have virus teeming in their nose and throat would be expected to transmit the virus, and the lack of symptoms in the immunized people who became infected suggests that the vaccine may have kept the virus levels in check.
But some studies have suggested that even people with no symptoms can have high amounts of coronavirus in their nose, noted Dr. Yvonne Maldonado, who represents the American Academy of Pediatrics at meetings of the federal Advisory Committee on Immunization Practices. The first person confirmed to be reinfected with the coronavirus, a 33-year-old man in Hong Kong, also did not have symptoms, but harbored enough virus to infect others.
Vaccinated people who have a high viral load but don’t have symptoms “would actually be, in some ways, even worse spreaders because they may be under a false sense of security,” Dr. Maldonado said.
Dr. Tal said she was concerned by monkey studies showing that some vaccinated animals did not get ill, but still had virus in their nose.
But those monkeys were intentionally exposed to massive amounts of virus and still had less virus than unvaccinated animals, said John Moore, a virologist at Weill Cornell Medicine in New York.
“The more you reduce viral load, the less likely you are to be transmissible,” Dr. Moore said. But “all of these are things where data trumps theory, and we need the data.”