I know that there's no immune response/adaptation of some (relatively) new viruses like HIV for which it's estimated that it would take at least 32,000 years for humans to develop a non-pathogenic response similar to that that some monkeys have to SIV.

But for more "run of the mill" viruses like new strains of influenza etc., do doses below the minimum infective dose (MID) sometimes act like a vaccine, i.e triggering immune system adaptation that later helps preventing a pathogenic response to a higher dose (above MID)?

2 Answers 2


There are clearly people who have antibodies to viruses such as SARS-CoV-2 who have no history of clinical symptoms. Presumably, they have been exposed to a low viral load which has been sufficient to trigger an immune response without the virus infecting sufficient cells to cause symptoms.

That is why they are saying that you don't need testing if you have been closer than 2 m to an infected person but have stayed there less than 10-15 minutes ( depending on the hospital issuing that information ).

Close contact can occur while caring for a patient, including:

being within approximately 6 feet (2 meters) of a patient with COVID-19 for a prolonged period of time.

having direct contact with infectious secretions from a patient with COVID-19. Infectious secretions may include sputum, serum, blood, and respiratory droplets. If close contact occurs while not wearing all recommended PPE, healthcare personnel may be at risk of infection.



The answer is NO. It only take one successful viroid particle to start an infection. Then you can always argue about how many particles you need to breath in, in order to ensure (statistically) that one sticks to your cellular lining and membrane to actually start the infection process. That's a different question.

  • 1
    If yo down-vote, please apply the courtesy to explain your decision so I can improve my answer.
    – not2qubit
    Mar 26, 2020 at 20:53
  • I didn't downvote but I think it might be because you didn't add the link sources on which you base your answer. Apr 26, 2020 at 15:48
  • We require references on this site as you should know now. Apr 27, 2020 at 5:53

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