My parents are both infected with the delta variant of COVID-19 and I have searched for the incubation period for that particular string. But I couldn't find any answer. Delta variant is highly contagious and it takes less time to show symptoms but what that time is,... No clue... Please help me cause I can't get a test because I'm not sick and I want to figure out if I can possibly be infected or not. So actually the question should be: from what time (starting when you just got infected) can you infect other people with COVID-19 delta. They are both fully vaccinated (2 shots) and I ame as well Sorry it's difficult to explain in English


1 Answer 1


You're asking for two (or three) slightly different (but closely related) things

The period between exposure and infection is called 'latent period', since the pathogen is present in a 'latent' stage, without clinical symptoms or signs of infection in the host.

The period between exposure and onset of clinical symptoms is called 'incubation period'.

The host may become infectious (i.e. able to transmit the pathogen to other hosts) at any moment of the infection. This moment will vary per pathogen.

For Delta, based on the Guangzhou outbreak this summer, the latent period (to PCR detection) has been estimated at 3-5 days interquartile range, fairly centered at 3.7 days average. (Mainstream press coverage here; that press article also says the incubation period is 4-6 days, but there's no clear source of data cited for that. It might come from China CDC, which has been quoted in the Chinese press as saying that the average incubation time was 4.4 days for the Guangdong outbreak.)

Public health England has put the Delta incubation period (exposure to onset of symptoms) to 2-6 days (interquartile range) with a median of four days for household exposure and to 3-6 days IQR (also with median of 4 days) for non-household exposure.

Whether someone whose infection is detectable by PCR (at low levels) also capable of transmitting the virus to other is slightly more contentious (and harder to test), but it's probably reasonable to assume the the capability to infect tracks closely the thresholds mentioned above.

Aside: a recent study from the UK has highlighted that protection against mere infection (with Delta) from a known "close and prolonged" exposure inside the household to a previously confirmed index case is less than what people might have hoped for (34% to 52% vaccine effectiveness, for a mixture of vaccines; most of those that had such breakthroughs had been vaccinated with the AZ one, but that's probably just a reflection of the UK's vaccine rollout structure.)

  • Thank you. I now have a much better understanding of it.
    – jessica
    Nov 1, 2021 at 14:55

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