Who should get vaccinated first?

Vaccination no doubt creates hope for a rapid recovery of our severely impacted economy and resumption of normal life from the long painful fight against the pandemic. The questions that concern most of us are which vaccine is more effective and whether the side effects are tolerable. Moreover, of greater interest to the policymakers is who should get vaccinated first, and which order of priority would result in the shortest time to herd immunity and/or the use of minimum resources. The point is that we don't have to vaccinate the weak or more vulnerable groups in order to protect them, but rather to vaccinate the spreaders in the community and hence protect the entire community. An elderly person could safely live in her nursing home if there were no infected caretakers or visitors!

In February 2021, Hong Kong government began offering free vaccine to the more vulnerable groups, including the elderly, medical and healthcare workers, and then teachers, taxi drivers, restaurant workers, etc., the rationale being the need for protection. However, taking a more scientific approach, the entire community is actually a network of people. Each individual has his or her own contacts. Some have more and some have less. An elderly person living in a nursing home under intermediate care would typically meet with three or four people (mostly caretakers or a couple of family visitors) daily. On the other hand, a cashier working in a convenience store could be in contact with hundreds of customers per day. In terms of the likelihood of spreading the virus, people having more contacts (technically called "degree" in a network) should more likely be the key spreaders.

A more effective approach may be to classify different groups according to the statistical average of the contact links per day. For instance, a taxi driver carries an average of 300 passengers a day; a restaurant waiter serves an average of 100 patrons a day; a teacher interacts with 50 students a day; and so on. Then, if we prioritize our order of vaccinating different groups in our community according to the average contact number of the groups, we should theoretically reach the nerd immunity state much quicker.

This is a research topic worth studying!

March 22, 2021