Map of life expectancy at birth from Global Education Project.

Tuesday, May 04, 2021

About this herd immunity concept . . .

You have no doubt read, or heard on the teevee, that experts are now saying we are unlikely to achieve herd immunity to the Covid-19 virus. Many people take this to be terrible news, a cause of despair, and even a reason not to bother to be vaccinated.

No, no, and no. The fact is the term herd immunity was bandied about far too much, and far too irresponsibly, from the beginning. It isn't even a sharply definable concept, as a matter of fact. The idea is that if enough people are immune, whether from vaccination or having been infected, the virus will not find enough susceptible hosts for trains of transmission to be maintained and then even people who are not immune are unlikely to be exposed, so we can forget about the virus. However, this was never a realistic prospect because the proportion of people who are immune will vary enormously from place to place for the foreseeable future. And places include places outside of the U.S. Furthermore, transmissibility and the required proportion of immune people also varies, depending on factors such as populations density, household structure, the kinds of work people do, and so on. 

What this means is that no matter what the proportion of immune people in the U.S. population overall, there will always be the possibility of an infectious person showing up, whether it is a visitor from abroad, someone who has taken a trip abroad, or a pocket within the U.S. where circulation continues. Right now in much of the world, where the epidemic is raging, only a tiny percentage of the population has been vaccinated. Here in the U.S., thanks to some evil politicians and liars on television, something like 30% of the population doesn't want to be vaccinated. Meanwhile, the virus mutates and more transmissible strains are circulating, putting the threshold for herd immunity even higher. 

However, this is not a disaster. People who are properly vaccinated are very safe for now, and as the proportion of people who are vaccinated rises, transmission will slow even if it doesn't stop entirely. As the most vulnerable people are most likely to be vaccinated, the stress on the health care system and the death rate will continue to decline. In time, we can hope that nearly all young children will have been vaccinated, or been infected while they are at very low risk of severe disease, and that some degree of immunity will be long lasting. Unfortunately we don't yet know about the latter proposition, and it matters a lot. If that does happen, Covid-19 will go the way of common childhood diseases that pose little threat. If not, we may need to get booster shots every year or two, but once we don't have to try to vaccinate the entire population all at once that can be handled as all vaccinations are now provided routinely.

In other words, this probably won't go away, but it will become manageable. Getting vaccination to low and middle income countries has to be a priority for the rich countries -- it's in our interest. And Tucker Carlson needs to eat shit and take a vow of silence. Here's a discussion at the NYT, if the paywall stops you Digby has pulled an excerpt.

1 comment:

Dr Porkenheimer said...

I believe that more people will warm up to the vaccines when they have had more real world beta testing. Remember, most of the vaccines used in the US are using a new technology.

Confidence is high.