What is desirable from a SARS-CoV-2 vaccine to stop Covid-19 pandemic?
Our goals for the effective management of Covid-19 pandemic are:
1. Prevent an epidemic
2. Extinguish an ongoing epidemic
To achieve these goals, we need to study two parameters for any vaccine:
1. Efficacy (probability of preventing infection)
2. Coverage (% of the population vaccinated)
Additional intervention (parameter):
Non- vaccine interventions, like social distancing
First, to prevent an epidemic:
Vaccine efficacy should be > 70% when the vaccination covers > 75% population. (In the absence of other interventions)
Second, to extinguish an ongoing epidemic and remove the need for other measures eg. social distancing:
The vaccine should have an efficacy > 80% with a 75% vaccine coverage.
Link: Vaccine Efficacy Needed for a COVID-19 Vaccine as the Sole Intervention to Prevent or Stop an Epidemic (American Journal of Preventive Medicine, 15 July 2020. Click here to read it.
COVID-19 vaccine trials including the WHO Solidarity Vaccines Trial
Requirements from a vaccine:
[1] A successful vaccine should reduce the risk by 50%, with sufficient precision to conclude that the true vaccine efficacy is > 30%.
[2] A vaccine with 50% efficacy could appreciably reduce COVID-19 incidence in vaccinated persons and might provide useful herd immunity.
[3] A rapidly introduced COVID-19 vaccine could lead to widespread deployment of a weakly effective vaccine (eg, reducing COVID-19 incidence by only 10–20%).
[4] If the trials are not of sufficient size and duration, we may also miss assessing whether the vaccine can make COVID-19 more hazardous (eg. disease enhancement).
[5] For a vaccine that halves risk the main result on short-term efficacy should emerge within 3–6 months. Placebo-controlled follow-up then continues until at least month 12.
Link: The Lancet, 27 Aug 2020
COVID-19 vaccine trials should seek worthwhile efficacy. Click here to read
