In the United States, The standard approach to distributing a routine vaccine is based on the assumption that sufficient doses will be available. Ideally, everyone then follows the recommendations of their doctor when it comes to being immunized against the germ in question. In practice, however, these two conditions are rarely fully met. Some people cannot get a vaccine; others refuse. (For the 2019-20 season, the influenza vaccine was distributed to roughly half the US population.) The next best vaccine score is to vaccinate enough people that there are too few along with those who are immune from infection available hosts so that the pathogen is widespread in the population – a situation known as herd immunity.
However, with a brand new disease like Covid-19, achieving herd immunity is especially difficult. It takes time to make enough vaccine to give to anyone who would benefit and then more time to distribute it. And no vaccine completely protects everyone who receives it. Despite these limitations, a vaccine can help. "We don't need a perfect vaccine" to achieve herd immunity, says Eric Toner, lead author of the Guidelines for the Allocation and Distribution of Vaccines created by the Johns Hopkins Bloomberg School of Public Health. But how many people need to be vaccinated to get there depends on how good the vaccine is. The more effective it is, the fewer people will need it. How this number of people turns out and how quickly we reach them also depends on how we decide to use these starting doses.
A previous vaccine shortage has helped highlight the critical importance of sales strategies. In 2009, the H1N1 flu strain known as swine flu emerged unexpectedly, causing production delays. So the C.D.C. had to decide who would come first for the limited doses. Because H1N1 appeared to be far more likely to get the disease in young people than older adults, the agency recommended that health care workers vaccinate as many people between the ages of 6 months and 24 years (as well as other high-risk groups) as possible prior to treatment in older adults. For seasonal influenza, policy at the time was to vaccinate those most susceptible to serious illness or death, including children between 6 months and 18 years old and adults over 50 years of age.
In an article earlier this year in Science, Alison Galvani of Yale University and Jan Medlock of Oregon State University argued that if we didn't just try Um, we could actually prevent more people from getting sick and dying from H1N1 and other flows To protect those most at risk, we have vaccinated those who are most likely to transmit the viruses. "Children aged 5 to 19 are responsible for most of the transmission and spread of infections to their parents' age groups," they wrote. Therefore, they showed that first vaccination would be most effective at protecting “the rest of the population” for people aged 5 to 19, as well as for people roughly the same age as their parents (30 to 39 years). Tens of thousands of infections and deaths would be prevented, as well as billions in economic costs. These findings led the C.D.C. Recommend that everyone aged 6 months and over receive a seasonal flu vaccine annually.