The new guidance only applies if it has been at least two weeks since your final dose, no more than three months since that dose, and as long as you do not develop symptoms.
“It is important to note that the CDC is not suggesting that someone who has been vaccinated cannot spread COVID-19 within the first 90 days after being fully vaccinated, nor are we suggesting that the expected protection of COVID-19 vaccines will disappear after 90 days,” says CDC spokesperson Kristen Nordlund told CNN by email. “The three months are in line with what the CDC currently recommends for people with natural infection, and we will continue to evaluate this period as we get more information about the duration of vaccine protection.”
Confused? Don’t worry, you are not the only one.
“Currently, there is limited information about how much COVID-19 vaccines can reduce transmission or how long protection lasts,” said Nordlund.
“However, we know that quarantine can be very harmful to the individual and also to society. The benefits of avoiding unnecessary quarantine, specifically for those who are fully vaccinated, are likely to outweigh the unknown risks of transmission from a vaccinated person.”
Furthermore, this does not mean that you can stop wearing a mask, keep your distance from others and follow other CDC guidelines. You are also not exempt from testing requirements for those returning from abroad.
Although the guidelines imply that vaccinated people may be less likely to transmit the virus, the CDC makes it clear that vaccine testing has largely focused on preventing symptomatic cases of Covid-19. This does not mean that people cannot catch the virus and spread it asymptomatically. But this is significantly more difficult to measure, experts say.
“There is no perfect measure to describe the likelihood that someone will transmit the virus,” said Dr. Megan Ranney, associate professor of emergency medicine at Brown University.
Measure transmission indirectly
Measuring Covid-19 transmission directly is difficult, so researchers use proxies to estimate how likely a person is to transmit the virus.
A potential proxy is viral load – the amount of viruses that people have circulating in their bodies. Research has shown that people with lower viral loads are less likely to transmit the virus.
A recent study in Israel found that people who were infected 12 to 28 days after the first dose of the Pfizer vaccine had viral loads four times less than if they had been infected in the first 12 days. Although the study was not peer-reviewed and does not include data after the second dose, Ranney said the findings were “really exciting”.
“This suggests that you are less likely to pass it on to others even after the first few weeks – even before you are fully immunized,” she said.
Another study on the AstraZeneca vaccine also suggested that it could affect transmission, but it did so using a different measure. The researchers collected nasal swabs from test participants in the UK every week and found that the rate of positive tests dropped by half after two doses of the vaccine.
None of these studies measured transmission directly – for example, tracking contacts from study volunteers to see if they were infected. But they give a positive signal of what the experts had suspected for some time, based on experiences with vaccines for other diseases.
“It is assumed, I think, that vaccines are also disrupting asymptomatic transmission” and preventing the virus from replicating in people’s noses and mouths, said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
“I think it’s probably true,” he said, adding, “I don’t know if we have all the i’s dotted and the crossed t’s.”
Limited data, limited recommendations
More studies that test people vaccinated regularly for Covid-19 will give doctors a better understanding of how vaccines affect transmissibility and for how long, Ranney said.
This is partly why the recommendation only applies for up to three months – because the CDC and vaccine manufacturers do not have much data available any longer after people have been vaccinated. “Certainly the vaccines will last more than three months,” said Hotez.
Ç
DC made similar updates to its quarantine guidelines in August, when it said that people who have recovered from Covid-19 in the past three months do not need to quarantine or be tested again, as long as they do not develop new symptoms. According to the agency, “the available evidence suggests that the majority of recovered individuals would have a degree of immunity for at least 3 months”, and reinfection appears to be unusual during that period.
But the risk is not zero. Still, despite the uncertainties, Hotez and Ranney said the new orientation is a step in the right direction.
“In a way, it is a welcome recommendation because, at some point, we have to start working towards normality and opening up the country,” said Hotez.