A just-announced policy change from the newly reinvigorated CDC specifies that persons who may have been exposed to COVID-19 no longer need to quarantine if they've been fully vaccinated within the previous 90 days. (People who aren't vaccinated are still supposed to quarantine for 14 days after they have been in close contact with someone who has COVID-19.) The new policy states:
At this time, vaccinated persons should continue to follow current guidance to protect themselves and others, including wearing a mask, staying at least 6 feet away from others, avoiding crowds, avoiding poorly ventilated spaces, covering coughs and sneezes, washing hands often, following CDC travel guidance, and following any applicable workplace or school guidance, including guidance related to personal protective equipment use or SARS-CoV-2 testing.
However, vaccinated persons with an exposure to someone with suspected or confirmed COVID-19 are not required to quarantine if they meet all of the following criteria [bold in original]:
- Are fully vaccinated (i.e., ≥2 weeks following receipt of the second dose in a 2-dose series, or ≥2 weeks following receipt of one dose of a single-dose vaccine)
- Are within 3 months following receipt of the last dose in the series
- Have remained asymptomatic since the current COVID-19 exposure
On the basis of the available evidence, this new policy might be premature.
The clinical trials, which tested the safety and efficacy of vaccines prior to their approval, focused on their ability to stop symptomatic infections. Efficacy was measured as the ability of the vaccine to prevent infection, which was defined as a positive nasal swab test for viral genetic material plus one or more symptoms (lung congestion, fever, loss of sense of smell or taste, etc.). The CDC offers only meager evidence to support the underlying premise of this policy—namely, that a vaccinated person's expected lower likelihood of symptomatic infection or severity of infection significantly reduces in any way his or her ability to spread the disease. As virologist Angela Rasmussen observed in a New York Times op-ed, "It's possible that vaccinated people are protected against COVID-19 themselves, but still spread SARS-CoV-2 to others who are not vaccinated."
CDC itself admits that "the risk of SARS-CoV-2 transmission from vaccinated persons to others is still uncertain." In addition, the prevention of illness or reduction of infectivity from vaccination is never 100%; indeed, in clinical trials, the just-approved Johnson & Johnson COVID-19 vaccine was 66% protective overall, 72% in the U.S.
CDC's rationale, as stated in the policy statement, is, "Although the risk of SARS-CoV-2 transmission from vaccinated persons to others is still uncertain, vaccination has been demonstrated to prevent symptomatic COVID-19; symptomatic and pre-symptomatic transmission is thought to have a greater role in transmission than purely asymptomatic transmission." Some support is lent to that speculation by a preliminary report of an Israeli study published earlier last month which suggests that people who are fully vaccinated and get infected may have less virus in their bodies, and, therefore, may be less likely to transmit an infectious dose to others.
CDC states that the waiver of "quarantine for people with vaccine-derived immunity aligns with quarantine recommendations for those with natural immunity [from having been infected with SARS-CoV-2], which eases implementation." However, a recent study based on a large cohort of UK National Health Service workers concluded, "People who have previously been infected with COVID-19 are likely to be protected against reinfection for several months, but could still carry the virus in their nose and throat and transmit it to others."
Thus, the CDC appears to be putting great stock in speculation that people who have been vaccinated or were previously infected with SARS-CoV-2 may harbor less virus, which, in turn, makes them less likely to spread infection. That seems to us somewhat tenuous, at best.
A DEADLY DISEASE CALLS FOR CONSERVATIVE POLICIES
The CDC offers this overarching rationale for the new guidance: "Additionally, individual and societal benefits of avoiding unnecessary quarantine may outweigh the potential but unknown risk of transmission, and facilitate the direction of public health resources to persons at highest risk for transmitting SARS-CoV-2 to others." But the CDC provides no metrics for defining "unnecessary" quarantines or for measuring the possible costs of the change in policy, which relegates policymaking to the realm of qualitative value judgments instead of hard (or even soft) data..
The CDC also omits any mention of other existing considerations, like the appearance of new SARS-CoV-2 "variants of concern," that might suggest caution before implementing this new policy. For example, a more transmissible—and seemingly deadlier—variant of the coronavirus called B.1.1.7 is becoming increasingly prevalent in the U.S., even as overall case numbers, hospitalizations, and deaths come down. It's not clear whether this variant, along with the South African (B.1.351) or Brazilian (P.1) variants, will cause numbers of infections (and thus hospitalizations and deaths) to surge once again. And although vaccination is effective in preventing illnesses caused by the UK variant, the South Africa and Brazil variants appear "to be better at avoiding immunity created by prior infection and some vaccines."
CDC's own website describes the serious concerns and unknowns raised by the more rapidly and easily transmitted UK, South Africa, and Brazil variants of SARS-CoV-2. In addition, there are other new variants of concern circulating in the United States. One, first identified in and now spreading in California, appears to be more transmissible and to raise patients' risk of admission to the intensive care unit (ICU) and death, according to a preprint reporting lab studies and epidemiological data. Another SARS-CoV-2 variant, B.1.526, currently circulating in New York, needs to be closely monitored because of "its ability to evade both monoclonal antibody and, to a certain extent, the vaccine-induced antibody," according to Dr. Anthony Fauci, a senior White House advisor and the director of the National Institute of Allergy and Infectious Diseases.
The rapid spread of these variants and the costs of the resulting infections suggest that greater, not less, caution may be needed to prevent their spread. The CDC's new, more lenient quarantine policy for people who have been vaccinated or previously infected with COVID-19 despite that risk is cause for alarm.
The CDC should at least caution that its new policy is tentative because further experience and data might indicate that quarantine is, in fact, appropriate for those exposed to SARS-CoV-2, even if they have been vaccinated or previously infected. With so many unknowns remaining about a deadly infectious disease that can spread exponentially, we need to be cautious with aspirational policies that can boomerang.
John J. Cohrssen is an attorney and statistician who served in senior positions for White House agencies including the Office of the Vice President. Henry I. Miller, a physician and molecular biologist, is a Senior Fellow at the Pacific Research Institute. He was the founding director of the FDA's Office of Biotechnology. You can find him online at henrymillermd.org or on Twitter at @henryimiller.