Moderna vaccine is nearly 95% effective, but NNTV = 176 to 1370
Dear EditorMODERNA VACCINE IS NEARLY 95% EFFECTIVE, BUT NNTV = 176 TO 1370
Moderna’s phase III trial has shown that, so far, the vaccine is 94.5% effective. (Mahase, BMJ 2020;371:m4471, November 17) As with the Pfizer vaccine news release, few numbers are provided, but we can approximate the absolute risk reduction for a vaccinated individual and the Number Needed To Vaccinate (NNTV): There were 90 cases of Covid-19 illness in a placebo group of 15,000 (0.006) and 5 cases in a vaccine group of 15,000 (0.00033). This yields an absolute risk reduction of 0.00567 and NNTV = 176 (1/0.00567). There were 11 severe illnesses, all in the placebo group, for an absolute risk reduction of 0.00073 and NNTV = 1370. So to prevent one severe illness 1370 individuals must be vaccinated. The other 1369 individuals are not saved from a severe illness, but are subject to vaccine adverse effects, whatever they may be and whenever we learn about them.
How does this compare with other vaccines? Before the measles vaccine became available 90% of children in North America had measles by age 10. Two doses of the vaccine are about 95% effective, so a vaccinated individual’s risk is reduced by 0.855 (0.90 x 0.95), and the NNTV = 1.17 (1/0.855); this is extraordinarily effective……On the other hand, it has been calculated that to prevent a single case of invasive meningococcal disease in North American infants with 3 doses of 4CMenB vaccine at least 33,000 infants must be vaccinated, so NNTV is > 33,000! (Dang et al, BMC Infect Dis 2012;12:202)
Shouldn’t absolute risk reduction be reported so individuals can make fully informed decisions about vaccinations?
ALLAN S. CUNNINGHAM 22 November 2020
Competing interests: No competing interests