Can you spread Covid-19 after vaccination?

Companies say the investigation is ongoing to determine the answer. Without vaccines, research has suggested that asymptomatic coronavirus transmission caused by Covid is responsible for about a quarter of infections.

The result, experts say, is that precautions will be needed such as wearing masks, socially distancing oneself and avoiding crowded spaces until the country approaches herd immunity, the point at which there are enough people immune to a disease because its spread is unlikely. Some studies have estimated that approximately 75% to 80% of the U.S. population needs to be immune to Covid-19 to achieve herd immunity, but that number is a moving target and could increase as new ones emerge. variants.

“Everyone has to keep putting on masks and we all have to do our part to reduce transmission, so it won’t be that hard to control,” says Marion Pepper, an immunologist and associate professor at the University of Washington in Seattle. “That’s really important.”

There are some indications that vaccination may reduce asymptomatic infection, which reduces transmission. Preliminary tests by Moderna showed that participants in a clinical trial who received the vaccine and who tested Covid between the first and second dose had a reduction of approximately two-thirds in asymptomatic infections. “This means that there is a substantial and substantial reduction in general infections from this first dose,” says Deepta Bhattacharya, an associate professor of immunobiology at the University of Arizona in Tucson.

Experts note that the data set was small and more results are needed. Larry Corey, a virologist at the Fred Hutchinson Cancer Research Center in Seattle, called the data “suggestive,” but said no conclusions should be drawn from limited evidence. Corey leads a federal vaccine testing program that conducts phase 3 clinical trials for multiple Covid-19 vaccines and proposed a study on U.S. university campuses that sought to examine whether Moderna’s vaccine prevents the spread of coronavirus. but the study was halted due to lack of funding and time constraints.

“To date there is very little information,” says Dr. Corey.

The issue of transmission means that those who receive the first vaccines do not change their behavior much. Claritza L. Rios, a 44-year-old emergency medicine physician in Oakland, California, received her first dose of the Pfizer vaccine on Jan. 4. Her husband, also an emergency doctor, received her a week earlier. Both must be paid for the second dose in late January.

But her in-laws, who are in their eighties and live on the streets, have yet to be vaccinated and probably won’t for at least another month. Her two children, ages 6 and 8, will have to wait many more months because vaccine trials in children under 12 have not yet begun.

“It won’t change anything until we’re 100% sure we won’t extend it to others,” Dr. Rios says. “We won’t see our parents and hug them until we’re 100% sure it’s safe to be with them.”

Coronavirus usually enters the body through the nose or mouth, says Dr. Bhattacharya. But the most serious disease of Covid-19 usually occurs in the lungs. Vaccines are injected into the bloodstream and antibodies develop in the blood before passing into the nose to prevent infection. “Antibodies can cross into the lungs a little more easily than into the nose or throat,” says Dr. Bhattacharya. “Therefore, it is much easier to prevent serious or symptomatic diseases” than infection, he explains.

Even after getting vaccinated, if someone is exposed to the virus, the body’s immune response can take a while to control an infection, says Dr. Pepper. The transmission potential depends on how quickly the infection is controlled.

“Most vaccines prevent disease rather than prevent infection,” says Anna Durbin, an international health professor at the Johns Hopkins Bloomberg School of Public Health who works in the AstraZeneca Covid-19 vaccine trial and who previously worked. in the Pfizer vaccine test. He believes that studies on Covid vaccines will eventually show a reduction in asymptomatic transmission, but not a complete elimination.

Even if vaccines don’t completely prevent transmission, they can help populations achieve herd immunity if enough people take it, says Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health who chairs the herd. vaccines of Advisory Committee on related biological products. “We can still achieve a lot even if it is shown that there is still some asymptomatic infection that occurs after vaccination,” says Dr. Mountain.

Significant asymptomatic transmission is unlikely to be exclusive to Covid-19, Dr. Monto says. Other viruses have not been studied so extensively. When the rubella vaccine came out, there were some documented asymptomatic reinfections, Dr. Monto says, but the herd’s immunity was eventually achieved.

One possible problem is whether significant segments of the population decide not to take the Covid-19 vaccine, says John R. Mascola, director of the National Vaccine Research Center for Allergy and Infectious Diseases.

“Until we have a powerful vaccine and the herd’s immunity, we should be thankful that it is possible to be really exposed to the virus of anyone, whether vaccinated or not,” he says. But if the vast majority of people get the vaccine, “some asymptomatic transmission won’t have a big public health implication,” he says.

Write to Sumathi Reddy at [email protected]