How many days are you contagious with delta

• NEWS
• 19 August 2021

People infected with the Delta variant generally do not have COVID-19 symptoms until two days after they start shedding the coronavirus.

1. Smriti Mallapaty

   1. Smriti Mallapaty is a senior reporter in Sydney, Australia.

People in Qingdao, China, are tested for COVID-19.Credit: AFP via Getty

People infected with the Delta variant of SARS-CoV-2 are more likely to spread the virus before developing symptoms than are people infected with earlier versions, suggests a detailed analysis of an outbreak in Guangdong, China1.

“It is just tougher to stop,” says Benjamin Cowling, an epidemiologist at the University of Hong Kong and a co-author of the study, which was posted on a preprint server on 13 August.

Cowling and his colleagues analysed exhaustive test data from 101 people in Guangdong who were infected with Delta between May and June this year, and data from those individuals’ close contacts. They found that, on average, people began having symptoms 5.8 days after infection with Delta — 1.8 days after they first tested positive for viral RNA. That left almost two days for individuals to shed viral RNA before they showed any sign of COVID-19.

A dangerous window

An earlier study2 and an unpublished analysis by Cowling and others estimate that before Delta emerged, individuals infected with SARS-CoV-2 took an average of 6.3 days to develop symptoms and 5.5 days to test positive for viral RNA, leaving a narrower window of 0.8 days for oblivious viral shedding.

In the latest work, the researchers also found that those infected with Delta had higher concentrations of viral particles, or viral load, in their bodies than did people infected with the original version of SARS-CoV-2. “Somehow the virus is appearing quicker and in higher amounts,” says Cowling.

As a result, 74% of infections with Delta took place during the presymptomatic phase — a higher proportion than for previous variants. This high rate “helps explain how this variant has been able to outpace both the wild-type virus and other variants to become the dominant strain worldwide”, says Barnaby Young, an infectious-disease clinician at the National Centre for Infectious Diseases in Singapore.

COVID vaccines slash viral spread – but Delta is an unknown

The researchers also calculated Delta’s ‘basic reproduction number’, or R0, which is the average number of people to whom every infected person will spread the virus in a susceptible population. They estimated that Delta has an R0 of 6.4, which is much higher than the R0 of 2–4 estimated for the original version of SARS-CoV-2, says Marm Kilpatrick, an infectious-disease researcher at the University of California, Santa Cruz. “Delta moves a bit faster, but is much more transmissible.”

A small number of study participants experienced ‘breakthrough infections’ with Delta after receiving two doses of an inactivated-virus COVID-19 vaccine. But the vaccine reduced participants’ viral loads at the peak of infection.

Vaccinated individuals were also 65% less likely than unvaccinated individuals to infect someone else, although the estimate was based on a very small sample size. This reduction “is significant and reassuring that COVID-19 vaccines remain effective and a vital part of our response to the pandemic”, says Young.

The study has not yet been peer reviewed.

References

1. Kang, M. et al. Preprint at medRxiv https://doi.org/10.1101/2021.08.12.21261991 (2021).

2. Xin, H. et al. Clin. Inf. Dis. https://doi.org/10.1093/cid/ciab501 (2021).

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Isolation and Precautions for People with COVID-19

Isolation and Precautions for People with COVID-19

Isolation and Exposure Calculator

A tool to help you determine if you need to isolate or take other steps to prevent spreading COVID-19.

If you have COVID-19, you can spread the virus to others. There are precautions you can take to prevent spreading it to others: isolation, masking, and avoiding contact with people who are at high risk of getting very sick. Isolation is used to separate people with confirmed or suspected COVID-19 from those without COVID-19.

These recommendations do not change based on COVID-19 Community Levels. If you have COVID-19, also see additional information on treatments that may be available to you.

This information is intended for a general audience. Healthcare professionals should see Ending Isolation and Precautions for People with COVID-19. This CDC guidance is meant to supplement—not replace—any federal, state, local, territorial, or tribal health and safety laws, rules, and regulations.

Regardless of vaccination status, you should isolate from others when you have COVID-19.

You should also isolate if you are sick and suspect that you have COVID-19 but do not yet have test results. If your results are positive, follow the full isolation recommendations below. If your results are negative, you can end your isolation.

IF YOU TEST

Negative

You can end your isolation

IF YOU TEST

Positive

Follow the full isolation recommendations below

When you have COVID-19, isolation is counted in days, as follows:

If you had no symptoms

• Day 0 is the day you were tested (not the day you received your positive test result)
• Day 1 is the first full day following the day you were tested
• If you develop symptoms within 10 days of when you were tested, the clock restarts at day 0 on the day of symptom onset

If you had symptoms

• Day 0 of isolation is the day of symptom onset, regardless of when you tested positive
• Day 1 is the first full day after the day your symptoms started

If you test positive for COVID-19, stay home for at least 5 days and isolate from others in your home.

You are likely most infectious during these first 5 days.

• Wear a high-quality mask if you must be around others at home and in public.
• Do not go places where you are unable to wear a mask. For travel guidance, see CDC’s Travel webpage.
• Do not travel.
• Stay home and separate from others as much as possible.
• Use a separate bathroom, if possible.
• Take steps to improve ventilation at home, if possible.
• Don’t share personal household items, like cups, towels, and utensils.
• Monitor your symptoms. If you have an emergency warning sign (like trouble breathing), seek emergency medical care immediately.
• Learn more about what to do if you have COVID-19.

End isolation based on how serious your COVID-19 symptoms were. Loss of taste and smell may persist for weeks or months after recovery and need not delay the end of isolation.

If you had no symptoms

You may end isolation after day 5.

If you had symptoms and:

Your symptoms are improving

You may end isolation after day 5 if:

• You are fever-free for 24 hours (without the use of fever-reducing medication).

Your symptoms are not improving

Continue to isolate until:

• You are fever-free for 24 hours (without the use of fever-reducing medication).
• Your symptoms are improving. 1

If you had symptoms and had:

Moderate illness (you experienced shortness of breath or had difficulty breathing)

You need to isolate through day 10.

Severe illness (you were hospitalized) or have a weakened immune system

• You need to isolate through day 10.
• Consult your doctor before ending isolation.
• Ending isolation without a viral test may not be an option for you.

If you are unsure if your symptoms are moderate or severe or if you have a weakened immune system, talk to a healthcare provider for further guidance.

Regardless of when you end isolation

Until at least day 11:

• Avoid being around people who are more likely to get very sick from COVID-19.
• Remember to wear a high-quality mask when indoors around others at home and in public.
• Do not go places where you are unable to wear a mask until you are able to discontinue masking (see below).
• For travel guidance, see CDC’s Travel webpage.

After you have ended isolation, when you are feeling better (no fever without the use of fever-reducing medications and symptoms improving),

• Wear your mask through day 10.

OR

• If you have access to antigen tests, you should consider using them. With two sequential negative tests 48 hours apart, you may remove your mask sooner than day 10.

Note: If your antigen test results1 are positive, you may still be infectious. You should continue wearing a mask and wait at least 48 hours before taking another test. Continue taking antigen tests at least 48 hours apart until you have two sequential negative results. This may mean you need to continue wearing a mask and testing beyond day 10.

After you have ended isolation, if your COVID-19 symptoms recur or worsen, restart your isolation at day 0. Talk to a healthcare provider if you have questions about your symptoms or when to end isolation.

[1] As noted in the Food and Drug Administration labeling for authorized over-the-counter antigen tests, negative test results do not rule out SARS-CoV-2 infection and should not be used as the sole basis for treatment or patient management decisions, including infection control decisions.

Isolate and take precautions if you have or suspect you have COVID-19

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