I’m Vaccinated. When Do I Need to Wear a Mask?

Mask guidance continues to change. Here’s what you need to know, depending on who you are, to protect yourself—and, most importantly, others.

WHEN THE CDC announced in mid-May that fully vaccinated people no longer needed to wear masks in most indoor settings, it felt like a milestone to many Americans, indicating that we might be one step closer to the end of the pandemic. It’s understandable, then, that the agency’s decision several weeks ago to bring back indoor mask recommendations even for vaccinated people led to anger, frustration, or confusion for many.

“It is a little bit confusing that the public is told at one point that the vaccine is effective enough that they can pretty much ditch their mask anywhere, and now, this is clearly a different recommendation because of the very high transmissibility of the Delta variant,” Dan Diekema, an infectious disease epidemiologist at the University of Iowa College of Medicine, says. “I think the CDC did the right thing, but it definitely puts members of the public in kind of a difficult situation in terms of making day-to-day decisions.”

But now that the circumstances have shifted, so should our behavior to deal with them.

“The vaccines are highly effective, but we know they’re not perfect, so it’s important to use complementary measures like masking for those areas with higher levels of Covid in the community,” Saskia Popescu, an assistant professor and epidemiologist at George Mason Universit, says.

But that doesn’t mean everyone has to mask up everywhere outside their house, vaccinated or not. Let’s break down when to wear a mask and why, and when you can set it aside.

Why Vaccinated People Still Need to Mask

First, let’s briefly review why the CDC changed their guidance in May, and then again more recently. The clinical trials for the Covid-19 vaccines tested how well the vaccines prevented disease, and they did that remarkably well. Then data in spring revealed the vaccines also appeared to prevent most infections, as in the ability of the virus to begin replicating after getting into the body. That’s unusual—most vaccines don’t prime the body so well that it can dispatch a pathogen before it even begins hijacking cells—but it appeared to be true for the mRNA vaccines. Blocking infection also blocks transmission: If the virus never starts replicating, you never shed it, so you’re not infectious to anyone. Hence the CDC’s advice in May that vaccinated folks can ditch their masks.

Along comes Delta. Though not actually “as contagious as chickenpox,” despite the CDC’s leaked internal document, Delta is about twice as contagious as the original coronavirus strain that swept the nation in 2020. According to a recent study, it has a basic reproduction number (R0) of 5-9, which means a person infected with the Delta variant of SARS-CoV-2 will infect about 5 to 9 other people on average, instead of the 2 to 3 of the previous strains. (Since R0 is an average, some people will infect no one, and others may infect twice as many people.)

Based on the most recent data, it seems Delta is so contagious because it replicates very quickly, producing about 1,000 times more virus particles than the original strain did. That’s partly why people infected with Delta become contagious sooner than with past variants, and it’s possibly why Delta seems to cause more breakthrough infections—but a mask reduces that risk further.

“People with Delta are shedding more virus, and if you’re around them for a long period of time, you’re going to be exposed to the minimum infectious dose in a shorter period of time than you would have otherwise,” Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization-International Vaccine Centre in Saskatchewan, Canada, says. “Wear a mask, reduce the numbers. It’s that simple.”

Since it replicates so quickly—often before vaccinated people’s immune systems can obliterate it—there’s a higher chance that a vaccinated person exposed to Delta might shed some virus during the few days it takes their body to clear the virus. Their body might successfully destroy the virus before the person ever knows they were infected and without causing symptoms, but if their viral load—the total virus particles in their body—was nearly as high as what’s seen in unvaccinated people in the first few days after exposure (as research suggests), they still could have transmitted the virus to others.

The good news is that vaccinated people aren’t as contagious as unvaccinated people, and they’re infectious for a shorter period of time, maybe a few days if they never have symptoms. But that might be all it takes to pass along the virus to someone more medically fragile than they are. Even if you’re healthy and vaccinated and can handle a couple days of feeling crappy while your body beats back a breakthrough infection, those you potentially infect may not be as lucky, especially if they’re immune-compromised or too young to be vaccinated.

Who Should Always Mask

Instead of a blanket recommendation that all vaccinated people should mask everywhere, the CDC identifies a few populations who should always mask up indoors, vaccinated or not, and then what other vaccinated folks should do. If you’re immune-compromised, follow the advice that Dorry Segev, a Johns Hopkins researcher and transplant surgeon, gives his patients: “Get vaccinated, act unvaccinated.”

That means wearing a mask in any indoor setting where you’re around people from outside your household and in any outdoor situations where it’s especially crowded or you’re in very close contact with people for an extended period (15 minutes or more.)

The CDC also advises all students, faculty, staff, and visitors in all schools to wear masks during the school day, a recommendation echoed by the American Academy of Pediatrics. Many students are too young to be vaccinated or otherwise unvaccinated (less than half of eligible teens have gotten the vaccine,) and others may have conditions making them high risk for infection and severe disease. Spending many hours of day together in the same room means it’s safest if everyone wears a mask to lower their likelihood of spewing virus around the classroom.

For Everyone Else

For people with properly functioning immune systems who aren’t in a school, the CDC advises fully vaccinated people to wear masks indoors if they’re around people from outside their household and in an area deemed by the CDC to havewith “substantial” or “high” transmission. Right now, though, that’s nearly the entire U.S. If you’re someone who obsessively checks local transmission levels each day and it drops below “substantial” transmission, there’s probably little enough virus circulating in your area that you’re not risking much by leaving your mask home. You can check your county’s transmission rates here. But with a virus as contagious as Delta, an area can flip from “low” transmission to “substantial” overnight. If you’re not checking local rates daily, it’s wise to assume everywhere in the US has high transmission until the Delta surge passes.

What About Outside?

Fortunately, outdoor transmission appears rare. The CDC doesn’t recommend masking outdoors unless the area has high transmission and it’s particularly crowded or you’re in close contact with others.

“You can think about it like peeing in the pool versus peeing in the ocean,” Rasmussen says. “If you’re peeing in a pool, more people around you are going to feel warmth because it’s a confined space. Obviously, if you pee in the ocean, people probably aren’t going to know. But if you’re in the middle of a huge group of people, like on a raft or something, and you piss, yeah, the people around you will probably be able to detect that.”

Outdoor concerts, for example, often have people tightly packed together for several hours and carry more risk, Popescu says. “Ventilation is important and there’s great ventilation outside, but that can only do so much when you’re shoulder-to-shoulder with hundreds of people for hours, yelling and shouting,” she says.

But I’m Healthy and a Risk-Taker

Aside from the guidelines above, there are two basic factors to think about in deciding whether to wear a mask: protecting yourself and protecting others. Unless you’ve been completely away from all people and had a negative Covid test that morning, you have to assume there’s always a chance you’re infected, and therefore that you could infect others.

If you’ll be around people at high risk for infection or severe disease—such as immune-compromised people, unvaccinated children, older adults, or someone with a high-risk condition—it’s safest to wear a mask to protect them from you. In places like grocery stores and pharmacies, where nearly everyone needs to go even if they’re in a high-risk group, the considerate thing to do is always wear a mask, regardless of local transmission rates, because you don’t know if you’ll be around vulnerable folks.

In places like restaurants, bars, and home get-togethers where you’re not required to wear a mask, your decision depends more on your own level of risk tolerance. How much risk of exposure are you comfortable with in exchange for not wearing a mask?

“There’s a framework of interventions that are important to prevent you from getting Covid, and then there’s people’s risk factors for a bad outcome,” says Anthony Harris, an epidemiologist at the University of Maryland School of Medicine. “If you combine those two hierarchies with someone’s own subjective assessment of risk, that’s how they should make decisions. There’s no black or white.”

Aside from local infection rates, you have several factors to consider:

  • How likely are you to develop severe disease if you have a breakthrough infection? If you’re in your 70s or immune-compromised, you may fare worse with a breakthrough infection even if it doesn’t kill you.
  • Are others around you vaccinated or unvaccinated? (If you don’t know, assume some are unvaccinated.)
  • How close are you to others?
  • How long are you there or how long are you close to others?
  • How big is the area?
  • How well ventilated is the area?

Mask Quality Matters Too

Also keep in mind that not all masks are created equally.

“I encourage people to focus on utilizing a quality mask, which is about fit and filtration,” Popscu says. “Ensuring the quality of masks becomes that much more important indoors.”

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, has advocated for months that Americans wear better protection than cloth masks, whose quality and effectiveness vary greatly. In the first half of 2020, public health experts discouraged the general public from wearing N95, KN95, and similar respirator masks so that healthcare workers had enough. But now, Osterholm says, healthcare workers and other professions who need respirators have plenty. There’s no reason the general public shouldn’t regularly wear these much more effective masks too. If nothing else, pair a cloth mask with a medical mask.

Ventilation, Ventilation, Ventilation

Of the factors above, that last one is among the most important, says Alex Huffman, an atmospheric chemist who studies bioaerosols at the University of Denver. The reason “outdoors is dramatically safer than indoors” is that virus particles exhaled by others don’t have a chance to build up. They just float up and away. Indoors is a different story.

The virus-containing aerosols that an infected person exhales “get mixed into the room and can build up in concentration if the ventilation is insufficient,” Huffman says. In a stagnant room where the aerosols build up, it takes fewer breaths to inhale enough virus to become infected. Room volume matters too, he says.

“The bigger, the better,” Huffman says. “If you breathe out aerosols into a bigger volume, it dilutes more quickly.” His research has found that a room’s height is one of the most influential factors in how much aerosols can build up.

Will Masking Ever End?

It’s easy to feel discouraged, maybe even a bit hopeless, with Delta surging and masks recommended for everyone again. But things will get better again, Harris says.

“It’s been a very long haul for everyone,” he says, but he points out how much better protected vaccinated people are now than a year ago. That’s not nothing. “I view this back-to-masks as a temporary setback, and it’s not going to be the new norm.”


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The effects of exercise therapy on the prognosis of patients with COVID-19

At the end of 2019, a pneumonia caused by a new pneumonia virus declares its fast spread throughout the World, and thus brings a great impact on global public Health, Health care system and economic development. On February 7, 2020, the World Health Organization (WHO) designated COVID-19 as Corona Virus Disease 2019 (COVID-19). Genome sequencing has confirmed that COVID-19 is similar to SARS-CoV and bat coronavirus, but the main source, mode of transmission, and mechanisms associated with human pathogenicity of this pandemic outbreak are unknown. At the beginning, COVID-19 is characterized by fever, dry cough, fatigue, and then dyspnea. In severe cases, it may progress to acute respiratory distress syndrome, septic shock, or even death Pneumonia often affects both lungs and presents mainly in the lower lobe, it is more severe in elderly patients over 70 years of age and in patients with various complications. Most children and young adults with SARS-COV-2 develop mild to moderate influenza-like symptoms and have a good prognosis. In addition to respiratory symptoms, some patients also experience digestive problems such as vomiting and diarrhea. The transmission mode of the virus is to enter the human body through mucous membranes, especially the mucous membranes of the nose and throat, and reach the lungs through the respiratory tract, and quickly replicate and spread. virus can be asymptomatic infection close (2 meters) cough or sneeze droplets spread, this is the main way for the spread of the virus. The fecal-oral route may also be a route of infection, as tests have shown that the virus is present in the feces and urine of COVID-19 patients. The main treatment for COVID-19 is symptomatic treatment, with critical patients receiving organ support. The use of drugs by antiviral drugs, protease inhibitors and a variety of drugs combined application, the purpose is to reduce the patient’s clinical symptoms. Traditional Chinese medicine (TCM) has also been widely used in COVID-19 patients in China. In clinical treatment, combined with conventional symptomatic treatment, good therapeutic effect has been achieved.

Exercise therapy refers to the use of equipment, freehand or patient’s own strength, exercise therapy through some means of movement (active or passive movement, etc.), so that patients get the whole body or local motor function, sensory function recovery training methods. Long-term outcomes for COVID-19 are not fully understood. Based on existing clinical studies, the possible results can be briefly categorized as follows:

  • 1. Lung injury that may develop, especially in severe cases of pneumonia or acute respiratory distress syndrome (ARDS);
  • 2. Complications during intensive care, such as fixation;
  • 3. Possible consequences and complications of neurological symptoms or disease caused by COVID-19;
  • 4. Lack of exercise, changes in eating habits, insomnia and psychological problems during isolation or isolation.

For patient rehabilitation exercise and abdominal breathing training exercise therapy can effectively increase the patient breathe out capacity, improve lung function. Through training exercise therapy in patients with upper limb muscles, lower limb muscles, walking training, breathing training, etc., can reduce patients with dyspnea condition, improve the patients’ pulmonary ventilation, pulmonary ventilation function, reduce the patients’ sputum, cough, improve function of limbs movement, make the patients life self-care ability, the effect of COVID – 19 has a benign prognosis.

Methods and analysis: 

The scheme was systematically reviewed in accordance with the preferred reporting items. We searched the following experimental databases: Cochrane Library, PubMed, EMBASE, Web of Science, China Biomedical Literature Database (CBM), China National Knowledge Infrastructure Database (CNKI), China Science and Wanfang Database. All trials using exercise therapy for rehabilitation of COVID-19 patients in the above database should be considered for inclusion. Relevant randomised controlled trials(RCTS), controlled before and after, interrupted time series and prospective analytic cohort studies regardless of publication date, language and geographic location, will be included. To summarize the therapeutic effect of exercise therapy on COVID-19 patients, high-quality literature was selected for data extraction and analysis. Two reviewers will independently screen titles, abstracts and full-text articles against inclusion criteria; perform data extraction and assess risk of bias in included studies. We will assess the certainty of the overall evidence using the Grading of Recommendations Assessment, Development and Evaluation approach and report findings accordingly.


Since the COVID-19 outbreak in 2020, more than 20 million people worldwide have been diagnosed with COVID-19, and all health care workers are looking for ways to improve the cure rate of the disease. As an important method of rehabilitation therapy, exercise therapy has been proved to improve the level of human function, promote the recovery of diseases, and improve the human immune ability. The main objective of this study was to provide reliable methods and credible evidence for exercise therapy to improve the prognosis of COVID-19 patients.

 December 18, 2020

Qiu, Guorong PhDJi, Yu PhD; Tan, Yajun PhDHe, Benxiang MDTan, Chunfeng BS; Wang, Zhuoling BS Gao, Hongpan BS

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Effects of interrupting prolonged sitting on postprandial glycemia and insulin responses: A network meta-analysis

  • Cardiovascular disease (CVD) is the leading cause of death worldwide. CVD survivors often experience a low quality of life and high cost of medical treatment and rehabilitation, which may cause great psychological and financial burden on patients and their families. Therefore, effective early interventions in the modifiable risk factors for CVD is of great significance to clinical and public health practice. Postprandial hyperglycemia and hyperinsulinemia are considered as independent predictors for the development of future CVD, and thus effective interventions to lower postprandial hyperglycemia and hyperinsulinemia could be important for CVD prevention.
  • Excessive sitting time is widespread and has been shown to be independently associated with the risk of CVD. Since observational studies have shown that interrupting prolonged sitting (PS) is associated with better cardiovascular risk factor profile, many experimental studies have assessed the effects of interrupting PS with physical activity (PA) breaks on postprandial glycemia and insulin responses among various populations. Most, if not all, studies have suggested that interrupting PS with moderate-intensity PA (MPA) to vigorous-intensity PA (VPA) breaks—and even light-intensity PA (LPA) breaks—can lead to positive effects on postprandial glycemia and/or insulin responses. Three pairwise meta-analyses conducted in 2015, 2018, and 2019 synthesized the findings of 6, 20, and 37experimental studies, respectively, and concluded that interrupting PS had positive effects on postprandial glycemia and insulin responses. For the following reason, however, additional research, using a novel network meta-analysis (NMA), is needed to quantitatively review and summarize the latest literature: (1) the conclusions of previous meta-analyses should be revisited given the increased numbers of new publications issued since the meta-analyses were conducted; (2) the optimal strategy for reducing postprandial glycemia and insulin responses among the different interventions should be identified using NMA, which allows for comparing multiple treatments sharing one common comparator treatment that were not directly compared with one another in head-to-head studies; and (3) NMA can integrate evidence retrieved from direct and indirect comparisons and thus has potential to improve the precision of intervention effect estimates.
  • Therefore, our review aims to perform an NMA to systematically evaluate the potential effects of various interventions that interrupt PS with PA on the postprandial glycemia and insulin responses among adults without chronic diseases. Identification of the effect of different characteristics of PA interventions that are optimally, or at least minimally, effective as strategies for postprandial glycemia and insulin control will help narrow the range of intervention strategies employed in future research and practice.
  • Purpose
  • This study aimed to evaluate the effectiveness of physical activity (PA) interrupting prolonged sitting (PS) on postprandial glycemia and insulin responses among adults.
  • Methods
  • PubMed, EMBASE, Cochrane Library, Web of Science, CINAHL, PsycINFO, and the China National Knowledge Infrastructure databases were searched through September 30, 2020. Randomized controlled trials (RCTs) that examined the effect of all forms of PA interrupting PS on postprandial glycemia and/or insulin responses among adults without chronic diseases were included in this study. The risk of bias of included studies was evaluated based on the Cochrane tool. A network meta-analysis was performed to estimate the summary standardized mean differences (SMDs) with 95% confidence intervals (95%CIs) with random effects.
  • Results
  • Thirty crossover RCTs were included in our review. These RCTs included 9 types of interventions that interrupted PS. When compared to PS by itself, light-intensity PA intermittent interrupting (LPA-INT) PS and moderate-intensity PA intermittent interrupting (MPA-INT) PS significantly lowered postprandial glycemia (SMD = –0.46, 95%CI: –0.70 to –0.21; SMD = –0.69, 95%CI: –1.00 to –0.37, respectively) and significantly reduced postprandial insulin response (SMD = –0.46, 95%CI: –0.66 to –0.26; SMD = –0.47, 95%CI: –0.77 to –0.17, respectively). Results of the clustered ranking plot indicated that MPA-INT was the most effective intervention in lowering postprandial glycemia and insulin responses.

July 2021


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Immediate effect of high-intensity exercise on brain-derived neurotrophic factor in healthy young adults: A systematic review and meta-analysis

  • Brain-derived neurotrophic factor (BDNF), a protein member of the neurotrophin family of growth factors, has been associated with the modulation of cognition, neuroplasticity, angiogenesis, and neural connectivity. The role of BDNF in the improvement of metabolic and cardiovascular functions and in delaying the onset of neurodegenerative diseases has received increased attention. Current evidence has pointed out the influence of BDNF levels on structural and functional brain changes, including hippocampal neurogenesis, long-term potentiation, increased hippocampal volume, and survival of new born hippocampal neurons. Thus, higher BDNF levels have been associated with better cognitive performance, attention, and spatial memory. Indeed, reduced BDNF concentrations have been found in patients with dementia, mild cognitive impairment, Alzheimer’s disease, and major depression.
  •  A previous meta-analysis reported that aerobic exercise programs with moderate-to-vigorous intensity in adolescents did not result in a significant increase in BDNF levels. Another systematic review reported a dose response in terms of the frequency and intensity of the programmed sessions in samples including people with a variety of health conditions (i.e., healthy individuals, chronic patients). However, neither of these explored the immediate effect of exercise at different intensities on BDNF levels. Although it is known that exercise intensity is correlated with heart rate (which has been linked to BDNF levels) and that the abovementioned reviews suggest the intensity of exercise is positively related to increases in BDNF levels, there is a lack of evidence about whether or not there is a threshold of exercise intensity from which a significant increase in BDNF concentrations can be observed. This information could be relevant to guide individual exercise prescriptions aimed at improving cognitive performance.
  • Therefore, the aim of the present study was to estimate the immediate changes in BDNF levels after exercise interventions at different intensities based on clinical trials in healthy young adults. Additionally, we explored whether acute changes in BDNF levels varied based on time spent on HIE (i.e., ≥30 or <30 min) or with respect to baseline cardiorespiratory fitness.
  • Background
  • Although brain-derived neurotrophic factor (BDNF) has been identified as a molecular biomarker of the neurophysiological effects induced by exercise, the acute effects of high-intensity exercise (HIE) on BDNF levels are inconclusive. This study aims to estimate the immediate effects of HIE on BDNF levels in healthy young adults.

·        Methods

  • A systematic search was conducted in the MEDLINE, Embase, Cochrane CENTRAL, and SportDiscus databases up to December 2020. Randomized controlled trials (RCTs) and non-RCTs reporting pre–post changes in serum or plasma BDNF after an acute intervention of HIE compared to a control condition were included. Pooled effect sizes (p-ESs) and 95% confidence intervals (95%CIs) were calculated for RCTs using a random effects model with Stata/SE (Version 15.0; StataCorp, College Station, TX, USA). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. PROPERO registration number: CRD42020221047.

·        Results

  • A total of 22 studies with 552 individuals (age range: 20–31 years; 59.1% male) were included. The meta-analysis included 10 RCTs that reported valid outcome data. Higher BDNF levels were observed when HIE interventions were compared with non-exercise (p-ES = 0.55, 95%CI: 0.12–0.98; I2 = 25.7%; n = 4 studies) and light-intensity exercise (p-ES = 0.78, 95%CI: 0.15–1.40; I2 = 52.4%; n = 3 studies) but not moderate-intensity exercise (p-ES = 0.93, 95%CI: –0.16 to 2.02; I2 = 88.5%; n = 4 studies) conditions

Available online 1 September 2021

RubénFernández-RodríguezaCeliaÁlvarez-BuenoIsabel A.Martínez-OrtegaVicenteMartínez-VizcaínoArthur EumannMesasBlancaNotario-Pacheco