The measurement of the entomological inoculation rate is considered with a certain confidence in the endemic areas. But it is not the case in the areas where the density of Anopheles mosquitoes and/or the sporozoitic index are very low. In this case, it is the sampling error limiting the average value of the inoculation rate which is taken into account. At times, this rate, cannot be calculated and an estimate of transmission is made from all kinds of other bases, parasitological, clinical or immunological. 

In areas where transmission is average, the annual entomological inoculation rate is not enough to characterize transmission: the seasonal transmission dynamics should also be taken into account. By way of theoretical example, two areas are considered where the entomological inoculation rate is 12 bites of infected Anopheles mosquito per capita (PAIH) per annum. In the first area, 1 PAIH is regularly observed in all the months of the year, whereas in the second, 12 PAIH is observed one month and none the other months: in these two areas, the malaria epidemiology is radically different. Transmission determines the intimacy of contact between Man and his parasite, which enables a more or less rapid premunition to be introduced. 
On the contrary, in those areas of very high or very low transmission, the seasonal dynamics are much smaller: a high transmission level is forcibly permanent or sub-permanent, a very low transmission level is obviously occasional.

It is also important to note that the entomological inoculation rate cannot be an exact measurement of transmission. In fact, many bites from Anopheles mosquitoes infected by sporozoites in the salivary glands fail to infect a man totally bereft of anti-malarial immunity. Experimental transmissions have shown that, on average, one volunteer out of two would develop a parasitemia after a single bite from an infected Anopheles mosquito.