Is SARS-CoV-2 contagious?
SARS-CoV-2, which causes COVID-19, is contagious; however, health experts are still uncertain about the exact mode of transmission. The CDC reports that SARS-CoV-2 can spread person to person through respiratory droplets. This may occur when an infected individual sneezes or coughs near another person.1 This means that transmission can occur between individuals spaced more than six feet apart and that the virus can linger in the air even after a person has left the area.2
Additionally, a study published November 19, 2020 in The Lancet Microbe, the SARS-CoV-2 virus is most contagious in the first five days after the onset of symptoms. This study also found that there was no difference in the viral loads among asymptomatic or symptomatic SARS-CoV-2-positive individuals, and research indicates that people without symptoms clear the virus quicker and are therefore less contagious.3
Airborne transmission of the virus, however, appears to play a significant role in virus transmission. On February 15, 2021, leading experts in industrial health, public health, and medicine sent a letter to the CDC and White House officials requesting that airborne, or inhalation, transmission of the SARS-CoV-2 virus be promptly addressed and emphasized that ensuring that frontline workers were provided with appropriate respirators and ventilation strategies to reduce the risk of infection and control the spread of the virus. These experts also noted that France, Germany, and Austria had recently mandated N95 filtering facepiece respirators (FFRs) for all frontline workers to reduce virus transmission.4
During a press conference referencing the letter, Dr. Donald Milton, MD, PhD, stated:
"Government officials must fully recognize inhalation exposure as a major way COVID-19 spreads and take immediate action to control and limit this exposure," and "For months the scientific evidence has been clear: Aerosol transmissions are a major way this virus spreads."5
Virus transmission may also occur when a person touches a contaminated object and then touches their mouth, nose, or eyes.6
There is also evidence that the virus can be spread through the fecal-oral route, which supports the recommendation for frequent handwashing. Infected feces can contaminate food, surfaces, and hands and potentially lead to illness.7 In China, health officials have begun using anal swabs to test for SARS-CoV-2 and report their accuracy to be superior to nasal and throat swabs. Anal swabbing was initiated after research noted that traces of the virus can remain longer in the anus than in the respiratory tract.8
Importantly, persons who test positive for SARS-CoV-2 virus may not go on to develop COVID-19 illness. On average, individuals exposed to SARS-CoV-2 will begin to develop COVID-19 symptoms within five days. Most people who develop symptoms will do so within 12 days. Rarely, symptoms may begin within two days or after 14 days.9
Persons that do go on to develop COVID-19 illness may experience mild to moderate symptoms and are generally no longer considered infectious 10 days after the onset of initial symptoms. Persons who develop severe COVID-19 illness are not likely to be infectious after 20 days post-symptom onset; however, persons who are severely immunocompromised may be capable of shedding the virus for longer than 20 days.10
The reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) test used to identify individuals infected with the SARS-CoV-2 virus uses a nasal swab to collect RNA from deep within the nasal cavity and is then reverse transcribed into DNA and amplified through cycles. Results from a PCR test are reported as a simple “yes” or “no” answer to the question of whether someone is infected.11
However, the validity of COVID-19 testing has continually been questioned by some health experts. There are reports that the PCR testing for SARS-CoV-2, the virus associated with COVID-19 illness, is too sensitive and adjustments are needed to distinguish people who have insignificant amounts of harmless viral material in their system versus people who are clinically infected with live virus. The most significant concern is that the number of detection cycles for the test is so high that it reports a positive result for people who have infectious live virus as well as a positive result for people who have only a few genetic fragments left over from a past infection and no longer pose a risk to others.12 13
A New York Times review published on August 29, 2020 reported on three sets of testing data that included cycle thresholds (CT) values compiled by officials in Massachusetts, New York and Nevada. The review found that “up to 90 percent of people testing positive barely carried any virus” and experts stated that tests using high CT values may be detecting not only live virus, but also genetic fragments; “leftovers from an infection that pose no particular risk” for contagiousness. The review reported that most tests used a CT value of 40, and noted the CDC’s acknowledgment that samples with a CT value above 33 cycles were unlikely to detect live virus.14
According to the U.S. Food and Drug Administration (FDA), cycle threshold ranges used to determine who is positive are set by commercial manufacturers and laboratories.15
A positive RT-qPCR test does not confirm whether a person is currently ill or will become ill in the future, whether they are infectious or will become infectious, whether they are recovered or recovering from COVID-19, or whether the RT-qPCR test identified a viral fragment from another coronavirus infection in the past. The RT-qPCR test is only capable of reporting that a person has come into contact with coronavirus RNA.16
Carl Heneghan, the director of the Centre for Evidence Based Medicine at the University of Oxford and editor of BMJ Evidence-Based Medicine has expressed concerns regarding the use of PCR testing to confirm a case of COVID-19 and noted:17
“In any other disease we would have a clearly defined specification that would usually involve signs, symptoms, and a test result… We are moving into a biotech world where the norms of clinical reasoning are going out of the window. A PCR test does not equal COVID-19; it should not, but in some definitions it does.”
A systematic review published in December 2020 in Clinical Infectious Diseases focused on COVID-19 viral cultures from PCR samples and assessed their infectious potential. A key finding from this review noted that the data suggests that complete live viruses are necessary for transmission of COVID-19, and not fragments that may be identified by PCR tests utilizing a high CT value. The review also estimated that the recovery of live virus from specimens with a CT value greater than 35 was only 8.3 percent, with five studies in the review reporting no growth in specimens with a CT value ranging from 24 to 35. The review also found that infectious potential declined after day 8, including cases with ongoing high viral loads.18
The CDC also reports that a person who has recovered from COVID-19 may have low levels of virus in their bodies for up to three months after diagnosis and may test positive, even though they are not spreading COVID-19.19
Addressing the controversial CT value aspect of COVID-19 PCR tests, on January 13, 2021, WHO issued a medical product alert and stated that persons who interpret results for specimens tested using PCR methodology should be aware that "careful interpretation of weak positive results is needed."20
A specimen may be considered weak if a high number of cycles are performed prior to virus detection. This may also mean that the person who provided the specimen might not be infectious.21 22 WHO is advising that a positive PCR test that is not consistent with the clinical presentation of COVID-19 should be confirmed through retesting of a new specimen.23
The CDC has revised testing guidelines for SARS-CoV-2 (COVID-19) multiple times and as of March 17, 2021 advised persons with symptoms of COVID-19 to get tested and stated that COVID-19 vaccination would not affect test results. Also noted was testing to screen asymptomatic persons when community risk or transmission levels are high, such as testing in the workplace and before travel.24 The CDC also recommends use of antigen testing when confirmatory testing is required. This guidance also recommends isolation individuals with positive test results, and interviewing and notification of close contacts for purposes of quarantine.25
Relating to negative test results, the CDC recommends that the unvaccinated continue to test and quarantine when exposed to SARS-CoV-2, however, states that the vaccinated do not need to test or quarantine when exposed to the virus.26
Like all testing, SARS-CoV-2 testing is not 100 percent accurate and false-positive and false-negative results can occur. False results are generally attributed to human error in processing, specimen contamination, or to the test’s sensitivity and specificity in accurately detecting the virus.27
Isolation and Quarantine after SARS-CoV-2 Virus Exposure
Since the declaration of the COVID-19 pandemic the CDC has recommended isolation and quarantine measures to limit the spread of SARS-CoV-2 infections. CDC quarantine guidelines have also been revised several times during the course of the declared pandemic.
Quarantine recommendations are intended for individuals who may have been exposed to the virus through close contact to a person with COVID-19. Close contact is defined as being withing six feet of an infected person for at least 15 minutes; caring for an infected individual at home; direct physical contact with an infected individual, such as kissing and hugging; droplets from an infected individual’s sneeze or cough getting on you; or sharing food utensils with an infected individual.28
Isolation is recommended for infected individuals and in simple terms means to stay away from others when you are ill.29
Guidance published on March 12, 2021 by the CDC updated quarantine guidelines and stated that persons in close contact to a COVID-19 positive person do not need to quarantine, if they have tested positive for SARS-CoV-2 within the previous three months, have recovered, and are asymptomatic. Additionally, persons who are considered fully vaccinated and who have received the vaccines in the past three months are not required to quarantine as long as they are asymptomatic. Persons in close contact with an infected individual are advised to stay at home for 14 days, and to isolate themselves while ill.30
Immunity after SARS-CoV-2 Infection
Researchers report that more than 95 percent of people who recover from SARS-CoV-2 infection had durable immunity to the virus for at least eight months.31
IMPORTANT NOTE: NVIC encourages you to become fully informed about covid-19 and the covid-19 vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.
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1 U.S. Centers for Disease Control and Prevention. COVID-19 How COVID-19 Spreads. Oct. 28, 2020.
2 U.S. Centers for Disease Control and Prevention. COVID-19 How COVID-19 Spreads. Oct. 28, 2020.
3 Van Beusekom, M. COVID-19 most contagious in first 5 days of illness, study finds. CIDRAP News Nov. 20, 2020.
4 Soucheray S. Experts push CDC, White House to address COVID-19 aerosol spread. CIDRAP News Feb. 17, 2021.
5 Soucheray S. Experts push CDC, White House to address COVID-19 aerosol spread. CIDRAP News Feb. 17, 2021.
6 U.S. Centers for Disease Control and Prevention. COVID-19 How COVID-19 Spreads. Oct. 28, 2020.
7 Soucheray S. Studies show COVID-19 virus likely has multiple infection routes. CIDRAP News Feb. 19, 2020.
8 Parpia R. Anal Swabs Used to Test for SARS-CoV-2 Virus in China. The Vaccine Reaction Feb. 14, 2021.
9 WebMD. Coronavirus Incubation period. Apr. 20, 2020.
10 U.S. Centers for Disease Control and Prevention. Interim Guidance on Duration of Isolation and Precautions for Adults with COVID-19. Feb. 13, 2021.
11 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.
12 Lenthang M. Experts: US COVID-19 positivity rate high due to ‘too sensitive’ tests. Daily Mail Aug. 30, 2020.
13 Tom MR., Mina MJ. To Interpret the SARS-CoV-2 Test, Consider the Cycle Threshold Value. Clin Infect Dis. 2020 May 21:ciaa619.
14 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.
15 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.
16 Cáceres B. Coronavirus Cases Plummet When PCR Tests Are Adjusted The Vaccine Reaction Sept. 29, 2020.
17 Mahase E. Covid-19: the problems with case counting. BMJ. 2020 Sep 3;370:m3374.
18 Jefferson T, Spencer EA, Brassey J, et al. Viral cultures for COVID-19 infectious potential assessment – a systematic review. Clinical Infectious Diseases December 2020; ciaa1764: https://doi.org/10.1093.
19 U.S. Centers for Disease Control and Prevention. COVID-19 Duration of Isolation and Precautions for Adults with COVID-19. Feb. 13, 2021.
20 WHO. WHO Information Notice for IVD Users 2020/05 Jan. 13, 2021.
21 Payne D. WHO warns of 'false positives' in COVID tests, says some patients might not be 'truly infected'. Just the News Jan. 22, 2021.
22 Cáceres M. WHO Issues New Guidance for Determining PCR Test Results. The Vaccine Reaction Feb. 21, 2021.
23 Lee M. WHO changes CCP Virus Test Criteria in Attempt to Reduce False Positives The Epoch Times Jan. 23, 2021.
24 U.S. Centers for Disease Control and Prevention. COVID-19 – Testing Overview: Key Points. Mar. 17, 2021.
25 U.S. Centers for Disease Control and Prevention. COVID-19 – Testing Overview: Test Types. Mar. 17, 2021.
26 U.S. Centers for Disease Control and Prevention. COVID-19 – Testing Overview: Test Types. Mar. 17, 2021.
27 Hou CY, False positive and false negative coronavirus test results explained The Hill May 7, 2020.
28 U.S. Centers for Disease Control and Prevention. COVID-19 – When to Quarantine. March 12, 2021.
29 U.S. Centers for Disease Control and Prevention. COVID-19 – When to Quarantine. March 12, 2021.
30 U.S. Centers for Disease Control and Prevention. COVID-19 – When to Quarantine. March 12, 2021.
31 National Institutes of Health (NIH) Lasting immunity found after recovery from COVID-19 NIH Research Matters Jan. 26, 2021.