COVID-19 Data Dispatch

Tag: isolation

  • Answering reader questions: Incubation period, vaccines coming this fall, nasal sprays

    I received a couple of reader questions in recent weeks that I’d like to answer here, in the hopes that my responses will be more broadly helpful. As a reminder, if you ever have a COVID-19 question that you’d like to ask, you can email me at betsy@coviddatadispatch.com, or send it anonymously through this Google form.

    COVID-19’s incubation period

    One reader asked:

    I’d love to learn more about COVID’s incubation period. I have read that it’s 2 to 14 days … but the median time seems to be on the low end (and could be as low as 24 hours?) How likely is it that it’s more like 14 days? I’d love to better understand this so that I know how to better handle exposures… Should I avoid someone who has had an exposure for two full weeks?

    This is a tricky question for two reasons. First, the incubation period—or the time between exposure to COVID-19 and starting to show symptoms of infection—does indeed vary a lot. One review of studies on this topic, posted as a preprint in May, found a range from two to seven days, though it can be even longer. The CDC recommends precautions for up to ten days after exposure.

    Second, the incubation period has changed as the coronavirus has mutated. The virus is constantly evolving to keep infecting us even as people build up immunity; shortening the incubation period is one of its strategies. Omicron has a notably shorter period than past variants; Katherine Wu at The Atlantic wrote an article about this in December 2021 that I think is still informative.

    The preprint I cited above found that Omicron had an average incubation period of 3.6 days, shorter than other variants. I think it’s reasonable to assume that this period has continued to get shorter as Omicron has evolved into the many lineages we’re dealing with now. But the pace of research on this topic has slowed somewhat (with less contact-tracing data available for scientists to work with), so it’s hard to say for certain.

    So, with these complexities in mind, how should one handle exposures? My personal strategy for this (noting that I’m not a doctor or qualified to give medical advice, just sharing my own experience) is to rely on a combination of timing, testing, and symptom monitoring. For the first couple of days after exposure, you wouldn’t be likely to have a positive test result even if you are infected, as it takes time for enough virus to build up in the body for tests to catch it. So, for those days, I’d just avoid people as much as possible.

    After three to four days, PCR tests would start to be effective, and after five to six days, rapid tests would be. So at that point, I’d start testing: using a mix of PCR and rapid tests over the course of several days, up to two weeks after exposure. Studies have shown that the more tests you do, the more likely you are to catch an infection (and this applies to both PCRs and rapids). Daily is the best strategy, but less frequent regimens can still be useful if your access to tests is limited. At the same time, I’d keep track of any new symptoms, as that can be a sign of infection even if all tests are negative.

    I’d personally be comfortable hanging out with someone who has had an exposure but consistent negative test results and no symptoms. But others who are less risk-tolerant than I am might avoid any contact for two weeks. The type of contact matters, too: a short, outdoor meeting or one with masks on is safer than a prolonged indoor, no-mask meeting.

    Vaccine effectiveness

    Another reader asked:

    Is there any information on the effectiveness of the latest vaccines, including vaccines that combine Covid and RSV, and are there similarities between these viruses (related?)

    As we head into respiratory virus season in the U.S., there will be, for the first time, vaccines available for all three major diseases: COVID-19, the flu, and RSV. I’ll talk about effectiveness for each one separately, because they are all separate vaccines for separate viruses. There’s no combined COVID-RSV vaccine on the market.

    COVID-19: We know the fall boosters will target XBB.1.5, a variant that has dominated COVID-19 spread in the U.S. recently. There isn’t much data available on these vaccines yet, because the companies developing them (Pfizer, Moderna, Novavax) have yet to present about their boosters to the FDA and CDC, as is the typical process. The CDC’s vaccine advisory committee is meeting this coming Tuesday to talk fall vaccines, though, so it’s likely we will see some data from that meeting.

    Also worth noting: some early laboratory studies suggest that vaccines based on XBB.1.5 will provide good protection against BA.2.86, despite concerns about differences between these variants. (More on this later in today’s issue.)

    Flu: Every year, scientists and health officials work together to update flu vaccines based on the influenza strains that are circulating around the world. Effectiveness can vary from year to year, depending on how well the shots match circulating strains.

    This week, we got a promising update about the 2023 flu vaccines: CDC scientists and colleagues studied how well these shots worked in the Southern Hemisphere, which has its flu season before the Northern Hemisphere. The vaccine reduced patients’ risk of flu-related hospitalization by 52%, based on data from several South American countries that participate in flu surveillance. This is pretty good by flu vaccine standards; see more context about the study in this article from TIME.

    RSV: There are two new RSV vaccines that will be available this fall, both authorized by the FDA and CDC in recent months. These vaccines—one produced by Pfizer, one by GSK—both did well in clinical trials, reducing participants’ risks of severe RSV symptoms by about 90% (for the first year after infection, with effectiveness declining over time).

    Both vaccines were authorized specifically for older adults, and Pfizer’s was also authorized for pregnant people as a protective measure for their newborns. We’ll get more data about these vaccines as the respiratory virus season progresses, but for now, experts are recommending that eligible adults do get the shots. This article from Yale Medicine goes into more details.

    Nasal sprays as COVID-19 protection

    Another reader asked:

    I’m thinking of researching what foods and supplement are anti-viral anti-COVID. I’m wondering if anyone has done any research on that?

    I haven’t seen too much research on about foods and supplements, since dietary options are usually not considered medical products for study. Generally, having a healthy diet can be considered helpful for reducing risk from many health conditions, but it’s not something to rely on as a precaution in the same way as you might rely on masking or cleaning air.

    Another thing you might try, though, would be nasal sprays to boost the immune system. I have yet to try these myself, but have seen them recommended on COVID-19 Safety Twitter and by cautious friends. The basic idea of these nasal sprays is to kill viruses in one’s upper respiratory tract, essentially blocking any coronavirus that might be present from spreading further. People take these sprays as a preventative measure before potential exposures.

    A couple of references on nasal sprays:

    https://twitter.com/Clean_Air_Club_/status/1685790242681331713

  • Sources and updates, October 16

    • New paper outlines the CDC’s COVID-19 data failures: A new study by researchers at Johns Hopkins and Stanford, published this week in PLOS One, outlines missing and poor-quality epidemiological data that hindered the U.S.’s response to COVID-19. The researchers reviewed hundreds of reports by the CDC and other health agencies, finding that public data couldn’t answer key questions ranging from how long immune system protection lasts after an infection to which occupations and settings face the highest COVID-19 risk. (H/t Amy Maxmen.)
    • White House pushes for improvements to indoor air quality: This week, the White House hosted a summit event on indoor air quality while launching new resources to help building owners improve their air. The summit featured talks by government officials and leading experts, discussing why indoor air quality is important—especially in public facilities like schools—and providing recommendations. (For more details, see this Twitter thread by Jon Levy.) Biden officials are calling on building owners to participate in the “Clean Air in Buildings Challenge,” which includes bringing in more clean outdoor air and enhancing filtration. While these are important steps for health improvements, some experts would like to see the federal government go further by mandating clean air.
    • Voters do actually support safety measures, poll shows: New polling data from the left-wing think tank Data for Progress suggests that, contrary to popular narratives, a majority of Americans understand that COVID-19 still poses risks and support safety measures. For example, 74% of likely voters support the federal government requiring schools and workplaces to improve indoor air quality, and 70% of likely voters understand that certain groups (disabled people, seniors, etc.) remain at high risk from COVID-19.
    • New study demonstrates long-term risks of infection: Another notable new paper from this week: researchers in Scotland used health records and surveys to follow about 33,000 people who tested positive for COVID-19, compared to 63,000 who did not. The patients were all surveyed at six, 12, and 18 months post-infection; between the six- and 18-month surveys, about 6% of the cohort had not recovered while 42% reported only partial recovery. As one of the biggest studies to date that doesn’t rely solely on health records, this paper shows how Long COVID can be devastating long-term for patients.
    • Further research backs up testing out of isolation: And one more study I wanted to highlight this week: researchers at the University of California San Francisco examined how long people remained contagious after a coronavirus infection. The study included over 60,000 people who were tested at community sites in San Francisco. Five days after symptoms started, the researchers found, about 80% of patients infected during the Omicron BA.1 period were still positive on rapid tests—suggesting that, as other studies have found in the past, five days is an inadequate isolation period. Rapid testing out of isolation is the way to go.

    All featured sources
  • The CDC’s isolation guidance is not based on data

    The CDC’s isolation guidance is not based on data

    A study published in the CDC’s own journal indicated that about half of people infected with Omicron are still contagious 5-10 days after their isolation period starts. Chart via CDC MMWR.

    Maybe it’s because I’m a twenty-something living in the Northeast, but: quite a few of my friends have gotten COVID-19 in the last couple of weeks. The number of messages and social media posts I’m seeing about positive rapid tests isn’t at the level it was during the Omicron surge, but it’s notable enough to inspire today’s review of the CDC’s isolation guidance.

    Remember how, in December, the CDC changed its recommendations for people who’d tested positive for COVID-19 to isolating for only five days instead of ten? And a bunch of experts were like, “Wait a second, I’m not sure if that’s sound science?” Well, studies since this guidance was changed have shown that, actually, a lot of people with COVID-19 are still contagious after five days. Yet the CDC has not revised its guidance at all.

    (Also, to make sure we’re clear on the terms: isolation means avoiding all other human beings because you know that you have a contagious disease and don’t want to infect others. Quarantine means avoiding other humans because you might have the disease, due to close contact with someone who does or another reason for suspicion.)

    The current CDC guidance still says that, if you test positive: “Stay home for 5 days and isolate from others in your home.” Yet, in recent weeks, I’ve had a couple of friends ask me: “Hey, so it’s been five days, but… I’m not sure I’m ready to rejoin society. Should I take a rapid test or something?”

    Yes. The answer is yes. Let’s unpack this.

    Studies indicating contagiousness after five days

    As this NPR article on isolating with Omicron points out, the CDC guidance was “largely based on data from prior variants.” At the time of this five-day recommendation, in late December, scientists were still learning about how Omicron compared to Delta, Alpha, and so on, particularly examining the mechanisms for its faster spread and lower severity.

    But now, almost four months later, we know more about Omicron. This version of the coronavirus, research suggests, is more capable of multiplying in the upper respiratory tract than other variants. People infected with Omicron are able to spread the virus within a shorter time compared to past strains, and they are able to spread it for a higher number of days—even if their symptoms are mild.

    One study that demonstrates this pattern is a preprint describing Omicron infections among National Basketball Association (NBA) players, compared to cases earlier in 2021. Researchers at Harvard’s and Yale’s public health schools, along with other collaborators, compared 97 Omicron cases to 107 Delta cases. NBA players are a great study subject for this type of research, because their association mandates frequent testing (including multiple tests over the course of a player’s infection).

    The big finding: five days after their Omicron infections started, about half of the basketball players were still testing positive with a PCR test—and showing significant viral load, indicating contagiousness. 25% were still contagious on day six, and 13% were still contagious on day seven. These patients also saw less of a consistent pattern in the time it took to reach their peak contagiousness than the players infected with Delta.

    From the NPR article:

    “For some people with omicron, it happens very, very fast. They turn positive and then they hit their peak very quickly. For others, it takes many days” – up to eight or even 10 days after turning positive, says the study’s senior author, Dr. Yonatan Grad, an associate professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health.

    While this NBA study is a preprint, other research has backed up its findings. One study from Japan, shared as a “preliminary report” in January, found that people infected with Omicron had the highest levels of viral RNA—indicating their highest levels of contagiousness—between three and six days after their symptoms started. The researchers saw a “marked decrease” in viral RNA only after ten days.

    Another preprint, from researchers at the University of Chicago (and antigen test proponent Michael Mina), examined Omicron infections among healthcare workers at the university medical center. Out of 309 rapid antigen tests performed on 260 healthcare workers, 134 (or about 43%) were positive results received five to ten days after these workers started experiencing symptoms.

    The highest test positivity rate for these workers, according to the study, was “among HCW returning for their first test on day 6 (58%).” In other words, more than half of the workers were still infectious six days after their infection began, even though the CDC guidance would’ve allowed them to return to work.

    Later in February, a study in the CDC’s Morbidity and Mortality Weekly Report (MMWR)—or, the CDC’s own journal—shared similar results. The report, authored by CDC researchers and practitioners at a healthcare system in rural Alaska, looked at antigen test results from hundreds of infections reported to this health system during the Omicron wave.

    The main finding: between five and nine days after patients were diagnosed with COVID-19, 54% (396 out of 729 patients) tested positive on rapid antigen tests. “Antigen tests might be a useful tool to guide recommendations for isolation after SARS-CoV-2 infection,” the authors wrote.

    Following this, an early March preprint from researchers at Massachusetts General Hospital, MIT, Harvard, and other collaborators analyzed infections among 56 people during the Delta and Omicron waves. This study used viral cultures to examine contagiousness directly, rather than simply looking at test results.

    Like past research, this study found that over half of patients (with both Omicron and Delta) were still contagious five days into their infections. About one-fourth were still contagious at day eight.

    Guidance for people testing positive

    All of the above studies suggest similar conclusions: about half of people infected with Omicron will still be contagious five days after their positive test results or the start of their symptoms, despite what the CDC’s guidance says. If you get infected with BA.2 in the coming surge, the best way to figure out whether you’re contagious after day five is by taking a rapid antigen test.

    In fact, for the highest accuracy (and peace of mind), I’d recommend taking two antigen tests, two days in a row. If both are negative, then you’re probably good to return to society—but maybe don’t travel to visit an elderly relative just yet.

    This two-rapid-test guidance comes from the U.K. Health Security Agency, which recommended in December that Brits could isolate for seven days instead of ten if they tested negative on days six and seven of their isolation. (The U.K.’s guidance has since become more lenient, but this is still a good rule for reference—more based in science than the CDC’s guidance.)

    What else should you do if you test positive? Here are a few recommendations that I’ve been giving friends and family:

    • Be prepared to isolate for a week or two, even if you may be able to leave isolation after a shorter period (with rapid tests).
    • After leaving isolation, wear a good mask (i.e. an N95 or KN95) in all public spaces.
    • Look into treatment options near you. The HHS has a database of publicly available COVID-19 therapeutics, while some localities (like New York City) have set up free delivery systems for these drugs.
    • There’s also the HHS Test to Treat program, which allows people to get tested for COVID-19 and receive treatment in one pharmacy visit. This program has faced a pretty uneven rollout so far, though.
    • Rest as much as possible, even if you have mild symptoms; patient advocates and researchers say that this reduces risk for developing Long COVID.

    More testing data