4 ms·

> ...R0 of 3 meant you needed 66%. This would mean it'd need to be even higher - the article says 82% For anyone curious, R0 = 3 means iff 2 in 3 people (66.6

> ...R0 of 3 meant you needed 66%. This would mean it'd need to be even higher - the article says 82% For anyone curious, R0 = 3 means iff 2 in 3 people (66.66%) [0] are immune would R0 drop to 1 [1]. So, when R0 = 5.7 (the value proposed by tfa for SARS-CoV-2), 4.7 in 5.7 (82.45%) would need to be immune for it to drop to 1 [1]. Why should R0 drop to 1 [1]? It means each case leads to only 1 successful transmission of the infection. This implies constant incidence over time. If a greater proportion are immune, then incidence will decline. Why "herd immunity" isn't enough? ...problems arise because herd immunity is not the same as biologic (immunologic) immunity; individuals protected only by indirect herd effects remain fully susceptible to infection, should they ever be exposed. This has advantages, in protecting individuals with contraindications to vaccination or those who for other reasons miss vaccination, but it also has its disadvantages. Measles and mumps outbreaks among university students, and pertussis in adults, are among examples of the consequences of accumulation of susceptible individuals who have not been protected by vaccination, and escaped infection because of a herd immunity effect earlier in their lives... This means that there is a need for immunization programs to maintain high vaccine coverage, together with surveillance and outbreak response capabilities, as numbers of susceptible individuals accumulate in older age groups. From: https://academic.oup.com/cid/article/52/7/911/299077 https://academic.oup.com/cid/article/52/7/911/299077 [0] This assumes a 100% effective vaccine (E = 1) in ((R0 − 1)/R0)/E. If, for a given vaccine, E < (R0 - 1)/R0, it'd be impossible to eliminate the infection through that vaccine. (R0 − 1)/R0 is known as the "herd immunity threshold." [1] What I really mean is R0 x S = 1. See: https://en.wikipedia.org/wiki/Endemic_(epidemiology) https://en.wikipedia.org/wiki/Endemic_(epidemiology)

zodiac 7y ago
Nitpick: changes in the number of immune people change R, not R0
- ignoramous 7y ago
  Yes, thanks. R or R-eff is more like it, but for the sake of simplicity I chose to instead leave a footnote about inaccurate usage of R0.
ineedasername 7y ago
Your comment belies the inaccuracy of your user name :)
hanniabu 7y ago
Would a greater percent of the population being immune lead to a greater chance for mutation since we're creating a higher barrier for survival of the virus?
- salawat 7y ago
  Nope. Viruses can only evolve within a host. I.e. while they are infected. If you've go the right vaccine, there won't be enough time for a virus to get a strong enough foothold to make that evolutionary leap, since mutations are always a shoot of the dice. Remember, there is no intelligence to evolution. Only happy coincidence. An immune population has the same probability of having a virus mutate in a particular infection, but has many, many fewer cranks on the mutation slot machine lever before the virus is eradicated. Where you run into problems is with things like dengue fever, where multiple strains can all provoke a single immune reaction, but the other strains aren't crippled as much by the antibodies as the original, and can actually use the immune response to increase the severity of the infection. I've read no papers that suggest that is a factor here.

zodiac 7y ago

Nitpick: changes in the number of immune people change R, not R0

ignoramous 7y ago
Yes, thanks. R or R-eff is more like it, but for the sake of simplicity I chose to instead leave a footnote about inaccurate usage of R0.

ineedasername 7y ago

Your comment belies the inaccuracy of your user name :)

hanniabu 7y ago

Would a greater percent of the population being immune lead to a greater chance for mutation since we're creating a higher barrier for survival of the virus?

salawat 7y ago
Nope. Viruses can only evolve within a host. I.e. while they are infected. If you've go the right vaccine, there won't be enough time for a virus to get a strong enough foothold to make that evolutionary leap, since mutations are always a shoot of the dice. Remember, there is no intelligence to evolution. Only happy coincidence. An immune population has the same probability of having a virus mutate in a particular infection, but has many, many fewer cranks on the mutation slot machine lever before the virus is eradicated. Where you run into problems is with things like dengue fever, where multiple strains can all provoke a single immune reaction, but the other strains aren't crippled as much by the antibodies as the original, and can actually use the immune response to increase the severity of the infection. I've read no papers that suggest that is a factor here.