In a recent study published in the Nature Human Behaviour journal, a team of researchers proposed a metapopulation model to assess the different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine allocation strategies adopted globally.
To date, the coronavirus disease 2019 (COVID-19) pandemic has caused over 376 million confirmed infections and 5.6 million deaths globally. SARS-CoV-2 vaccines are much needed to curb this spread and reduce public mortality. As of 30 January 2022, a total of 9.9 billion vaccine doses had been administered globally, and yet there is a staggering imbalance in vaccine distribution.
In high-income countries (HICs), over 70% of people are fully vaccinated while in low- and middle-income countries (LMICs), only 4% are fully vaccinated. This global vaccine inequity can lead to long-lasting consequences against public health and worsen the spread of the virus.
About the study
The present study assessed the various SARS-CoV-2 vaccine allocation strategies employed by HICs and LMICs globally and estimated the effect of global vaccine inequity on global vaccine effectiveness.
In this study, countries were classified as HICs and LMICs owing to their abilities to mass-produce vaccines. As per strategies for equitable global allocation of vaccines, four prioritization criteria, namely prevalence, population size, incidence, and mortality rate are utilized to provide vaccines and vaccine-related supplies to all countries, irrespective of their wealth. However, a portion (χ) of the available vaccines are bought by the HICs while the remaining are distributed among the LMICs.
The number of COVID-19 cases emerging under equitable and inequitable vaccine allocation strategies was investigated based on the population size of the countries. The study also assessed the effects of various vaccine donation strategies by countries in which the prevalence of COVID-19 infections was below a specified threshold (Ithr). Furthermore, varied allow-donation vaccine allocation strategies were tested with a focus on larger population countries prioritized for receiving the vaccines. The impact of vaccine donations if HIC donated vaccines to only their geographically neighboring LMICs was also investigated.
The study results showed that inequitable allocation of vaccines led to a rapid decline in COVID-19 incidences in the HICs and a slower decrease in infections in LMICs. This, in turn, caused more infections in the LMICs, thus extending the global duration of the pandemic. Furthermore, in the inequitable vaccine allocation scenario, a rebound of COVID-19 cases in LMICs was observed. HICs also experienced an increase in rebound cases as newer strains emerged in the LMICs.
Although under equitable vaccine allocation strategies, all four criteria led to similar pandemic durations, the researchers noted that prioritizing countries with bigger population sizes for vaccine allocation caused a slight increase in COVID-19 infections and related mortality globally. However, prioritizing vaccines to highly populated countries can reduce the overall prevalence of highly transmissible SARS-CoV-2 strains. Equitable vaccine distribution was found to reduce the global transmission of new viral strains, while allocating a larger share of vaccine supply to HICs led to faster transmission of newer strains globally.
The allow-donation vaccine allocation strategies benefitted all LMICs irrespective of the number of vaccines donated, although donation of more vaccines led to a significant reduction in mortality in LMICs. It was also observed that even small donations of vaccines made by HICs even when the local cases were high can effectively curb the spread of the virus globally. Furthermore, HICs donating vaccines only to their neighboring LMICs notably increased cumulative mortality in the LMICs, while only a small difference was observed in the cumulative mortality in HICs. Without a reduction in LMIC cases, the local epidemic in HICs cannot be fully eliminated due to continuous importations from the LMICs. Thus, HICs can further benefit from donating their excess vaccines to LMICs.
The study results indicated that prioritizing vaccination in countries with higher prevalence and mortality related to COVID-19 infections is necessary to limit the spread of the SARS-CoV-2 within the countries. However, in the case of highly transmissible VOCs, countries with dense populations should be prioritized for vaccine allocation. The increase in transmissibility of newly emerged SARS-CoV-2 strains when vaccines supply was primarily allocated to HICs underlined the disadvantages of inequitable vaccine allocation which led to higher mortality in HICs as well as LMICs.
Altogether, inequity in vaccine allocation provided only short-term benefits to HICs while increasing the number of COVID-19 infections and related deaths in both LMICs and HICs eventually. Equitable global vaccine allocation can effectively reduce the spread and mortality of the disease while also preventing the emergence and transmission of new SARS-CoV-2 strains. Global cooperation in the face of an unprecedented pandemic can be help achieve vaccine equity for both HICs and LMICs.