Vaccines have the potential to end the COVID-19 pandemic but it may be some time before they can make a major difference according to Data Evaluation and Learning for Viral Epidemics (DELVE), a multi-disciplinary group convened by the Royal Society.

Huge progress has been made through international collaboration with 200 vaccines in development and a number in trials that look promising.  However the report, SARS-CoV-2 vaccine development & implementation; scenarios, options, key decisions highlights the challenges involved, including that the initial vaccines might be only partially effective, might not be effective for some groups, might provide only short lived immunity, and have many problems to be solved around rapid scale-up in manufacture, distribution and acceptability.

Dr Fiona Culley of the National Heart and Lung Institute at Imperial College London and one of the lead authors of the report said: “Vaccines are held up as our best chance of getting our lives back to some sense of normality, but we have to be realistic.  The path to successful vaccines is filled with potential problems in finding vaccines that will work effectively in the ways we need and in being able to roll them out.  Planning now for the different scenarios that might play out will give us the best chance of taking rapid advantage of any vaccines that are proven to be safe and effective.”

Key issues identified in the report include:

• Potential differences in the ability of vaccines to protect against transmission and disease. 
• Likely variability of the effectiveness of vaccines in different populations, such as the elderly. 
• Possible short half-life of immunity provided by vaccines, meaning that multiple doses or boosters might be needed to achieve immunity. 
• Vaccines providing only partial immunity will require higher vaccination rates to achieve the same levels of protection in a population. 
• The need to establish systems for careful data collection to monitor population effectiveness and safety.
• The logistical challenges of manufacturing and delivering a global immunization programme are enormous and some of the most promising vaccine candidates (e.g. RNA vaccines such as the candidate being developed at Imperial College, London) are using technologies that have not been manufactured at scale before.
• Public trust in a vaccine programme will have to be established and maintained.

The report outlines different ways in which vaccines might be used to fight the pandemic. 

• Vaccines could be targeted to high risk groups, such as older people and those with existing health problems, health care workers and other priority groups. This would be the most likely scenario when supplies are limited. In this situation the virus would continue to circulate. Some vaccines might not effective at protecting older people. 
• Vaccinating the wider population. The aim here is to reduce transmission until herd immunity is produced and the virus is largely eliminated, although outbreaks might still occur. This would require a vaccine that was effective and acceptable in the majority of people and ideally gives long lived immunity but would require a large number of doses.
• Vaccines could be targeted as part of a rapid response to sporadic outbreaks. This would require a vaccine that offers rapid protection against disease or spread of the virus.  It would also require; continuous and effective testing and strong community engagement; and rapid administration and sufficient doses.

The report concludes that, should effective and safe vaccines be developed; global coordination of vaccine purchase, production and distribution is needed; availability, uptake, effectiveness and long term safety must be closely monitored; financial support must be maintained for the development of a second generation of vaccines; the SARS-CoV-2 virus must be closely monitored for vaccine-escape mutations; and that global collaboration to invest in research training and the infrastructure to deliver vaccine programmes is maintained to ensure preparedness for future pandemics. 

See more from Data Evaluation and Learning for Viral Epidemics (DELVE).