Using a system of time-dynamical equations, we investigate how daily mobility indices, such as the homestay percentage above the pre-COVID normal ($$H\%$$
H
%
; or H-forcing), and the vaccinated percentage ($$V_c\%$$
V
c
%
; or V-forcing) impact the net reproductive rate (R0) of COVID-19 in ten island nations as a prototype, and then, extending it to 124 countries worldwide. Our H- and V-forcing model of R0 can explain the new trends in 106 countries. The disease transmission can be controlled by forcing down $$R0(H,V_c) < 1$$
R
0
(
H
,
V
c
)
<
1
with an enforcement of continuous $$H > 40\%$$
H
>
40
%
in $$93\%$$
93
%
of countries with $$0\%$$
0
%
vaccinated plus recovered, $$V_p$$
V
p
. The required critical $$H\%$$
H
%
decreases with increasing $$V_p\%$$
V
p
%
, dropping it down to $$20\%$$
20
%
with $$25\% V_p$$
25
%
V
p
, and further down to $$8\%$$
8
%
with $$50\% V_p$$
50
%
V
p
. However, the regulations on $$H\%$$
H
%
are context-dependent and country-specific. Our model gives insights into forecasting and controlling the disease’s transmission behaviour when the effectiveness of the vaccines is a concern due to new variants, and/or there are delays in vaccination rollout programs.