Answer:
About 28,671,342 people
Step-by-step explanation:
This is compound growth problem. This goes by the formula:

Where
F is the future amount (in 3 years)
P is the present amount (28.5 million)
r is the rate of growth (0.4% = 0.4/100 = 0.004)
t is the time in years (3 years)
We first, need to find the rate of growth annually. It is given 0.4% every 2 years, so in 1 year that would be:
0.4%/2 = 0.2% = 0.002
Now, we put the information into formula and solve:

So, around 28,671,342 people will be infected in 3 years.