During a press conference Feb. 23, Gov. Phil Scott announced the state had decided to lift Vermont’s travel quarantine for people who had received both doses of the Covid-19 vaccine, and also allow them to gather with members of another household — the first easing of gathering restrictions since the holidays.
A key reason for loosening the gathering rules, Scott suggested, is that the Centers for Disease Control’s guidance says the vaccine stalls transmission of the virus from person to person.
“We’re doing this because the CDC guidance changed earlier this month,” Scott said. “Because they concluded that not only do vaccines protect you from Covid-19, but they also prevent you from spreading it, which is very encouraging news.”
That’s not entirely true.
While a developing body of evidence suggests that vaccines do significantly lessen Covid-19 transmission, the specific guidance Scott was citing highlights uncertainty about how effective immunizations are in preventing the virus’s spread from person to person. The federal agency urges vaccinated people to stay cautious.
“While mRNA Covid-19 vaccines have demonstrated high efficacy at preventing severe and symptomatic Covid-19, there is currently limited information on how much the vaccines might reduce transmission and how long protection lasts,” says the CDC guidance, last updated on Feb. 10. “In addition, the efficacy of the vaccines against emerging SARS-CoV-2 variants is not known.”
Vaccinated people should continue to be cautious in their behavior, too, by “wearing a mask, staying at least 6 feet away from others, avoiding crowds, avoiding poorly ventilated spaces, covering coughs and sneezes, washing hands often,” the CDC guidance says.
However, several recent studies suggest the CDC’s description of how effective vaccines are in curbing transmission is more conservative than their findings. On its face, Scott’s statement that vaccines prevent people from spreading the virus appears solid, those early studies suggest.
A widely reported Cambridge University study of vaccinated UK hospital workers released last week, for example, found that the Pfizer vaccine could significantly reduce transmission after just one dose.
A separate UK study, released a few days prior, indicated that a single vaccine dose was up to 70% effective in reducing cases. Two shots of the Pfizer or Astrazeneca vaccine boosted that figure to 85%.
The studies are promising. But it’s still too early — and the data too raw — to say definitely how effective vaccines are in limiting Covid-19 transmission, experts say.
“There's a growing body of evidence that suggests that the vaccine greatly reduces your chances of both getting infected, and likely passing the virus on,” said A. Marm Kilpatrick, an infectious disease biologist at the University of California, Santa Cruz. “But the data for both of those parts are limited, a little bit incomplete, and not quite the gold standard kind of data we'd like to have. They’re enough for a ballpark estimate, but not a super precise one.”
Most importantly, Kilpatrick said, the data appear clear on one thing: The vaccine does not provide 100% assurance against catching Covid-19.
“So if you get vaccinated, and it’s just you and the people around you aren’t vaccinated, there’s certainly a non-trivial chance that you could get infected and pass it on to that person,” he said, echoing a message Dr. Anthony Fauci delivered on CNN last week.
While it takes a conservative track on identifying how effective vaccines are in limiting transmission, the CDC guidance does explain that vaccinated people may be suited for different treatment than the rest of the population in some cases.
An earlier passage of the guidance, for instance, states that people who’ve received the vaccine need not quarantine if they come into contact with someone who has the virus.
That passage — a shift from the agency’s earlier quarantine policy — was what Scott intended to cite in his comments explaining the state’s policy change, said his press secretary, Jason Maulucci.
“With the CDC changing its guidance to no longer require quarantine for fully vaccinated individuals who are a close contact to someone with Covid-19, along with studies indicating vaccines significantly reduce transmission, the governor’s restart team … felt it was appropriate to make the initial changes for travel and small gatherings, and believe we can methodically take additional steps forward,” Maulucci said in an email to VTDigger.
“Like all the state’s guidance changes, this decision was made with input and sign-off from Health Commissioner Mark Levine and State Epidemiologist Patsy Kelso,” he added.
Scott has received praise throughout the pandemic for his adherence to science, as he has led Vermont through one of the nation’s more successful Covid-19 responses. Fauci called Vermont a “national model” in how to navigate the pandemic when he joined the governor’s press conference in November.
Guidance about the proper ways people should act once they’ve gotten their shots has not always been clear as the vaccine rolls out around the country.
With a lack of solid data on the virus’s transmissibility among vaccinated people, and months to go before the country’s entire population is vaccinated, Kilpatrick offered a message he acknowledges people are weary of hearing: that better times are just around the corner and even people who’ve gotten shots should exercise caution until consequences of particular behaviors come into sharper focus.
That doesn’t mean that people who’ve gotten the vaccine can’t enjoy some of the activities they may have avoided for the past year, he said.
“The way I try to think about it is to imagine tiers of things you would have done with varying risk levels,” Kilpatrick said. “I think being vaccinated allows you to move up a tier, but not throw away the whole risk table.”
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