Mainly cost/benefit analysis. Using vaccines has a cost, both in dollars and in risk. That cost may be very low (cheap safe vaccines, like measles vaccine), or may be relatively high (smallpox vaccine is relatively risky, with around a 1 in 300,000 chance of moderate to severe side effects); but there is always some cost.

Vaccines may not have any significant benefit. I live in the urban USA; it's unlikely that an Ebola vaccine would offer me any benefit (as of the current situation in 2019). Very few people in 2019 have a significant chance of being exposed to smallpox, since it's extinct in the wild; the benefit of universal smallpox vaccine would be small.

So if the risk of a vaccine is greater than the benefit, delivering the vaccine would be more harmful than good. This calculation is done as a routine, and the vaccines people receive are known to be ones that confer more benefit than risk.

In fact, with vaccines, the benefit needs to be much higher than the risk, because with vaccines the benefit is invisible (nothing happens - you don't die of measles) while the risk is something that happens. Typically, vaccine benefit/cost ratios are very high, for that reason.

Monetary cost is also a factor. It may seem harsh to think that saving a child's life with a vaccine is given a price, but at some point the finite supply of money can be used more effectively elsewhere. If it costs a billion dollars to give a particular vaccine, and it ends up saving one life, is that the best use of money? Could it be better spent on nutrition, sanitation, etc?

This applies to quite a few diseases. There are, in academic labs and in the freezers of pharmaceutical companies, vaccines against a lot of pathogens that are not being used, because the cost is too great for the benefit. That's an equation that changes all the time; it applied to the Ebola vaccines at one point, but in the face of an Ebola outbreak those vaccines -- in those areas -- are now cost-effective.

Finally, there are a handful of pathogens for which a reasonably-priced good vaccine would certainly be cost-effective (HIV, malaria, tuberculosis, for example) but for which reasonably-priced good vaccines don't, because vaccines are sometimes really hard to make.

Mainly cost/benefit analysis. Using vaccines has a cost, both in dollars and in risk. That cost may be very low (cheap safe vaccines, like measles vaccine), or may be relatively high (smallpox vaccine is relatively risky, with around a 1 in 300,000 chance of moderate to severe side effects); but there is always some cost.

Vaccines may not have any significant benefit. I live in the urban USA; it's unlikely that an Ebola vaccine would offer me any benefit (as of the current situation in 2019). Very few people in 2019 have a significant chance of being exposed to smallpox, since it's extinct in the wild; the benefit of universal smallpox vaccine would be small.

So if the risk of a vaccine is greater than the benefit, delivering the vaccine would be more harmful than good. This calculation is done as a routine, and the vaccines people receive are known to be ones that confer more benefit than risk.

In fact, with vaccines, the benefit needs to be much higher than the risk, because with vaccines the benefit is invisible (nothing happens - you don't die of measles) while the risk is something that happens. Typically, vaccine benefit/cost ratios are very high, for that reason.

Monetary cost is also a factor. It may seem harsh to think that saving a child's life with a vaccine is given a price, but at some point the finite supply of money can be used more effectively elsewhere. If it costs a billion dollars to give a particular vaccine, and it ends up saving one life, is that the best use of money? Could it be better spent on nutrition, sanitation, etc?

This applies to quite a few diseases. There are, in academic labs and in the freezers of pharmaceutical companies, vaccines against a lot of pathogens that are not being used, because the cost is too great for the benefit. That's an equation that changes all the time; it applied to the Ebola vaccines at one point, but in the face of an Ebola outbreak those vaccines -- in those areas -- are now cost-effective.

Finally, there are a handful of pathogens for which a reasonably-priced good vaccine would certainly be cost-effective (HIV, malaria, tuberculosis, for example) but for which reasonably-priced good vaccines don't exist, because vaccines are sometimes really hard to make.

Mainly cost/benefit analysis. Using vaccines has a cost, both in dollars and in risk. That cost may be very low (cheap safe vaccines, like measles vaccine), or may be relatively high (smallpox vaccine is relatively risky, with around a 1 in 300,000 chance of moderate to severe side effects); but there is always some cost.

Vaccines may not have any significant benefit. I live in the urban USA; it's unlikely that an Ebola vaccine would offer me any benefit (as of the current situation in 2019). Very few people in 2019 have a significant chance of being exposed to smallpox, since it's extinct in the wild; the benefit of a smallpox vaccine would be small.

So if the risk of a vaccine is greater than the benefit, delivering the vaccine would be more harmful than good. This calculation is done as a routine, and the vaccine people receive are known to be ones that confer more benefit than risk.

In fact, with vaccines, the benefit needs to be much higher than the risk, because with vaccines the benefit is invisible (nothing happens - you don't die of measles) while the risk is something that happens. Typically, vaccine benefit/cost ratios are very high, for that reason.

Monetary cost is also a factor. It may seem harsh to think that saving a child's life with a vaccine is given a price, but at some point the finite supply of money can be used more effectively elsewhere. If it costs a billion dollars to give a particular vaccine, and it ends up saving one life, is that the best use of money? Could it be better spent on nutrition, sanitation, etc?

This applies to quite a few diseases. There are, in academic labs and in the freezers of pharmaceutical companies, vaccines against a lot of pathogens that are not being used, because the cost is too great for the benefit. That's an equation that changes all the time; it applied to the Ebola vaccines at one point, but in the face of an Ebola outbreak those vaccines -- in those areas -- are now cost-effective.

Finally, there are a handful of pathogens for which a reasonably-priced good vaccine would certainly be cost-effective (HIV, malaria, tuberculosis, for example) but for which reasonably-priced good vaccines don't, because vaccines are sometimes really hard to make.

Mainly cost/benefit analysis. Using vaccines has a cost, both in dollars and in risk. That cost may be very low (cheap safe vaccines, like measles vaccine), or may be relatively high (smallpox vaccine is relatively risky, with around a 1 in 300,000 chance of moderate to severe side effects); but there is always some cost.

Vaccines may not have any significant benefit. I live in the urban USA; it's unlikely that an Ebola vaccine would offer me any benefit (as of the current situation in 2019). Very few people in 2019 have a significant chance of being exposed to smallpox, since it's extinct in the wild; the benefit of universal smallpox vaccine would be small.

So if the risk of a vaccine is greater than the benefit, delivering the vaccine would be more harmful than good. This calculation is done as a routine, and the vaccines people receive are known to be ones that confer more benefit than risk.

In fact, with vaccines, the benefit needs to be much higher than the risk, because with vaccines the benefit is invisible (nothing happens - you don't die of measles) while the risk is something that happens. Typically, vaccine benefit/cost ratios are very high, for that reason.

Monetary cost is also a factor. It may seem harsh to think that saving a child's life with a vaccine is given a price, but at some point the finite supply of money can be used more effectively elsewhere. If it costs a billion dollars to give a particular vaccine, and it ends up saving one life, is that the best use of money? Could it be better spent on nutrition, sanitation, etc?

This applies to quite a few diseases. There are, in academic labs and in the freezers of pharmaceutical companies, vaccines against a lot of pathogens that are not being used, because the cost is too great for the benefit. That's an equation that changes all the time; it applied to the Ebola vaccines at one point, but in the face of an Ebola outbreak those vaccines -- in those areas -- are now cost-effective.

Finally, there are a handful of pathogens for which a reasonably-priced good vaccine would certainly be cost-effective (HIV, malaria, tuberculosis, for example) but for which reasonably-priced good vaccines don't, because vaccines are sometimes really hard to make.