Disease & Vaccine Information

Is SARS-CoV-2 Contagious?

Updated September 05, 2022


covid-19

SARS-CoV-2, which causes COVID-19, is contagious and is transmitted through aerosolized particles and respiratory droplets. These particles and droplets can be inhaled or can enter the mouth, nose, or eyes.1

The theories on the mode of transmission of SARS-CoV-2, however, changed several times throughout the pandemic. Prior to early May 2021, the CDC reported that SARS-CoV-2 was primarily spread person to person through respiratory droplets and was most often transmitted when an infected individual sneezed or coughed near another person. This meant that transmission could occur between individuals spaced more than six feet apart and that the virus could linger in the air even after a person had left the area.2

In early May 2021, the CDC updated information regarding SARS-CoV-2 transmission and acknowledged that airborne transmission of the virus was also a primary mode of transmission.3 This acknowledgement, however, occurred nearly three months after leading experts in industrial health, public health, and medicine had 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.4

The CDC also acknowledges that SARS-CoV-2 transmission can occur when a person touches a contaminated object and then touches their mouth, nose, or eyes.5

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 has the potential to cause illness.6 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.7

A study published November 19, 2020 in The Lancet Microbe found that the SARS-CoV-2 virus was most contagious in the first five days after the onset of symptoms. This study also reported that there was no difference in the viral loads among asymptomatic or symptomatic SARS-CoV-2-positive individuals, and research indicated that people without symptoms clear the virus quicker and therefore less contagious.8 Research studies have also found that viral loads among vaccinated and unvaccinated SARS-CoV-2 positive people to be similar.9 10

A study conducted in the UK found that the SARS-CoV-2 virus lost 90 percent of its virulence within 20 minutes of being exhaled. After only 10 minutes, the virus lost 50 percent of its ability to infect. Humidity of the environment was also determined to play a role in the ability of the virus to infect. When the environment had a humidity level of less than 50 percent, the virus lost its ability to infect within 10 seconds.11 12

SARS-CoV-2 Testing

Importantly, persons who test positive for the 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.13

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, and longer than 140 days after testing positive for SARS-CoV-2.14

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.15

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.16 17

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.18

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.19

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.20

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:21

“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.22

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-19.23

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."24

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.25 26 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.27

The CDC has revised testing guidelines for SARS-CoV-2 (COVID-19) multiple times. As of August 28, 2022, the CDC is recommending that persons with symptoms of COVID-19 should be tested. Persons who have been in close contact with an infected person are also being advised to test at least five days after exposure. Persons who may have contact with an individual considered at high-risk for COVID-19 are advised to consider testing before contact, specifically if community transmission of the virus is moderate or high. Testing is not advised for asymptomatic individuals who have recovered from COVID-19 in the previous 30 days. If a person tested positive within 31 to 90 days, antigen testing for COVID-19 is recommended. 28

Antigen testing, frequently completed at home, however, is considered less reliable to diagnose COVID-19. Public health officials report that a single negative antigen test result does not necessarily rule out infection and recommend multiple testing (serial testing), repeated at least 48 hours apart.29

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.30

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.

As of August 24, 2022, the CDC is recommending that individuals who are exposed to SARS-CoV-2 should take immediate precautions. This includes wearing a good quality mask when around others both at home and in public spaces for at least ten days, and self-monitoring for symptoms of infection. COVID-19 testing is recommended on the sixth day after exposure. If the test result is positive, immediate isolation is advised. Precautions are recommended for at least ten days post-exposure even if a COVID-19 test is negative.31

The CDC is recommending that persons who test positive for COVID-19 isolate for at least 5 days if they are asymptomatic or their symptoms are resolving. Mask use when around others is recommended for another 5 days. The CDC also states that if it is not possible to quarantine for 5 days then a person should wear a well-fitted mask for at least 10 days when around others. If antigen testing is available, infected individuals can opt to test at least 48 hours apart until two sequential tests are negative. Should symptoms of COVID-19 return, individuals are advised to restart isolation.32

COVID-19 positive health care workers (HCW) are advised to quarantine for 10 days, or 7 days with a negative test if they have no symptoms or their symptoms are resolving. In the case of staff shortages, HCW may return to work after five days of quarantine if they are asymptomatic or their symptoms are resolving. If staffing is critical, COVID-19 positive HCW are being advised by the CDC that they can return to work if asymptomatic or mildly symptomatic.33

Immunity after SARS-CoV-2 infection

In January 2021, researchers reported that more than 95 percent of people who recovered from SARS-CoV-2 infection had durable immunity to the virus for at least eight months.34 Another study conducted by researchers at the Washington University School of Medicine in St. Louis found that persons who recover from COVID-19 illness, including those with asymptomatic and mild cases, continued to have lasting immunity upon recovery. Study researchers also speculated that immunity following COVID-19 infection would likely endure long-term.35

A study conducted by the Cleveland Clinic Health System in June 2021 involving 52,238 employees found that "Not one of the 1,359 previously infected subjects who remained unvaccinated had a [Covid-19 infection over the duration of the study” and vaccination did not reduce the risk. Study authors concluded that persons previously infected with SARS-CoV-2 were unlikely to benefit from COVID-19 vaccination.36 Another study specific to health care workers in an urban Massachusetts setting between December of 2020 and September of 2021, when the Delta variant was most prominent, also reported no cases of re-infection with SARS-CoV-2 among those previously infected.37

An August 25, 2021 retrospective study of Israel’s second largest HMO, yet to undergo peer review, compared 673,676 vaccinated individuals who had not been previously infected by SARS-CoV-2, 62,883 unvaccinated individuals and 42,099 previously infected individuals with a single vaccine dose. The study found that natural immunity “confers longer lasting and stronger protection against infection, symptomatic disease, and hospitalization caused by the Delta variant.”38

According to a CDC report published in January 2022 on cases and hospitalizations by COVID-19 vaccination status conducted in New York and California between May 2021 and November 2021, unvaccinated individuals with a history of natural SARS-CoV-2 infection had infection rates of between 14.7 and 29 times lower than unvaccinated individuals without prior infection. In contrast, COVID-19-vaccinated individuals with a past history of SARS-CoV-2 infection were noted to have infection rates that were only between 4.5 and 6.2 times lower. Additionally, hospitalization rates among persons with natural immunity were reported to be between 2 and 6 times lower than those who were vaccinated and had no prior infection.39

Over one hundred studies have reported natural immunity to be equal or better than vaccine acquired immunity.40 41

According to the CDC, as of early October 2021, there have been approximately 146.6 million COVID-19 infections in the U.S.42 A survey of blood donor samples completed in December 2021 and updated in February 2022 found that nearly 95 percent of the U.S. population over age 16 have antibodies to COVID-19, either through infection or vaccination.43 In April 2022, health officials estimated that approximately 75 percent of U.S. infants and children from birth to 11 years had previously been infected.44

The CDC has acknowledged that they have no evidence that any person with natural immunity due to past infection has been able to transmit the virus to another individual.45

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.


References:

1 U.S. Center for Disease Control and Prevention. How COVID-19 Spreads. In: COVID-19. Aug. 11, 2022.

2 U.S. Centers for Disease Control and Prevention. How COVID-19 Spreads. In: COVID-19. Oct. 28, 2020.

3 U.S. Centers for Disease Control and Prevention. How COVID-19 Spreads. In: COVID-19. May. 13, 2021.

4 Soucheray S. Experts push CDC, White House to address COVID-19 aerosol spread. CIDRAP News Feb. 17, 2021.

5 U.S. Centers for Disease Control and Prevention. How COVID-19 Spreads. In: COVID-19. Aug. 11, 2022.

6 Soucheray S. Studies show COVID-19 virus likely has multiple infection routes. CIDRAP News. Feb. 19, 2020.

7 Parpia R. Anal Swabs Used to Test for SARS-CoV-2 Virus in China. The Vaccine Reaction Feb. 14, 2021.

8 Van Beusekom, M. COVID-19 most contagious in first 5 days of illness, study finds. CIDRAP News Nov. 20, 2020.

9 Acharya CB, Schrom J, Mitchell AM. et al. No Significant Difference in Viral Load Between Vaccinated and Unvaccinated, Asymptomatic and Symptomatic Groups When Infected with SARS-CoV-2 Delta Variant. medRxiv Oct. 5, 2021.

10 Riemersma KK, Grogen BE, Kita-Yarbro A. et al. Shedding of Infectious SARS-CoV-2 Despite Vaccination. medRxiv Nov. 6, 2021.

11 TVR Staff. Study Finds SARS-CoV-2 Much Less Infectious After 20 Minutes in Air. The Vaccine Reaction Jan. 17, 2022.

12 Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. July 5, 2022;119(27):e2200109119.

13 WebMD. Coronavirus Incubation period. Feb. 3, 2022

14 U.S. Centers for Disease Control and Prevention. Ending Isolation and Precautions for People with COVID-19: Interim Guidance. In: COVID-19. Jan. 14, 2022.

15 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.

16 Lenthang M. Experts: US COVID-19 positivity rate high due to ‘too sensitive’ tests. Daily Mail Aug. 30, 2020.

17 Tom MR., Mina MJ. To Interpret the SARS-CoV-2 Test, Consider the Cycle Threshold Value. Clin Infect Dis. November 2020; 71(16):2252-2254.

18 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.

19 Mandavilli A. Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be. The New York Times Aug. 29, 2020.

20 Cáceres B. Coronavirus Cases Plummet When PCR Tests Are Adjusted The Vaccine Reaction Sept. 29, 2020.

21 Mahase E. Covid-19: the problems with case counting. BMJ Sept. 3, 2020; 370:m3374.

22 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.

23 U.S. Centers for Disease Control and Prevention. Ending Isolation and Precautions for People with COVID-19: Interim Guidance. In: COVID-19. Jan. 14, 2022.

24 WHO. WHO Information Notice for IVD Users 2020/05. Jan. 13, 2021.

25 Payne D. WHO warns of 'false positives' in COVID tests, says some patients might not be 'truly infected'. Just the News Jan. 22, 2021.

26 Cáceres M. WHO Issues New Guidance for Determining PCR Test Results. The Vaccine Reaction Feb. 21, 2021.

27 Lee M. WHO Modifies CCP Virus Test Guidelines, Warns Against Overreliance on PCR Results. The Epoch Times Jan. 26, 2021.

28 U.S. Centers for Disease Control and Prevention. COVID-19 Testing: What You Need to Know. In: COVID-19. Aug. 11, 2022.

29 U.S. Food and Drug Administration. COVID-19 Testing: What You Need to Know. In: COVID-19. Aug. 11, 2022.

30 Hou CY. False positive and false negative coronavirus test results explained The Hill May 7, 2020.

31 U.S. Centers for Disease Control and Prevention. What to Do If You Were Exposed to COVID-19. In: COVID-19. Aug. 24, 2022.

32 U.S. Centers for Disease Control and Prevention. Isolation and Precautions for People with COVID-19. In: COVID-19. Aug. 11, 2022.

33 U.S. Centers for Disease Control and Prevention. Interim Guidance for Managing Healthcare Personnel with SARS-CoV-2 Infection or Exposure to SARS-CoV-2. In: COVID-19. Jan. 21, 2022

34 National Institutes of Health (NIH) Lasting immunity found after recovery from COVID-19. NIH Research Matters Jan. 26, 2021.

35 Washington University School of Medicine in St. Louis. Good news: Mild COVID-19 induces lasting antibody protection. May 24, 2021.

36 Shrestha NK, Burke PC, Nowacki AS. et al. Necessity of COVID-19 Vaccination in Persons Who Have Already Had COVID-19. Clin Infect Dis. Jan 13, 2022. Epub ahead of print.

37 Lan FY, Sidossis A, Iliaki E. et al. Continued Effectiveness of COVID-19 Vaccination among Urban Healthcare Workers during Delta Variant Predominance. BMC Infect Dis. May 12, 2022;22(1):457.

38 Gazit S, Shlezinger R, Perez G, et al. Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections. medRxiv Aug. 25, 2021.

39 León TM, Dorabawila V, Nelson L, et al. COVID-19 Cases and Hospitalizations by COVID-19 Vaccination Status and Previous COVID-19 Diagnosis — California and New York, May–November 2021. MMWR Jan. 28, 2022;71:125–131.

40 Alexander PE. 150 Plus Research Studies Affirm Naturally Acquired Immunity to Covid-19: Documented, Linked, and Quoted. Brownstone Institute Oct. 17, 2021.

41 Attkisson S. Covid-19 natural immunity compared to vaccine-induced immunity: The definitive summary. Mar. 11, 2022.

42 U.S. Centers for Disease Control and Prevention. Estimated COVID-19 Infections, Symptomatic Illnesses, Hospitalizations, and Deaths in the United States. In: Estimated COVID-19 Burden. Aug. 12, 2022.

43 U.S. Centers for Disease Control and Prevention. Nationwide COVID-19 Infection- and Vaccination-Induced Antibody Seroprevalence (Blood donations). Feb. 18, 2022.

44 U.S. Centers for Disease Control and Prevention. Seroprevalence of Infection-Induced SARS-CoV-2 Antibodies – United States, September 2021 – February 2022. MMWR Apr. 29 2022; 71(17): 606-608.

45 Stieber Z. CDC: No Record of Naturally Immune Transmitting COVID-19. The Epoch Times Nov. 13, 2021.

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