Yeah, no doubt there'd be casualties, but I think the government would be able to evacuate people fast enough to avert most of them.
Btw, are we talking world-wide pandemic here, or just in America? Because if it's just in the US or something, then the other countries take the chance and blow us to shit with nukes, killing us and the titans. If worldwide, then there probably wouldn't be any nukes launched.
Anyway, assuming we don't just blow everything up with nukes, yes, modern day weapons would be VERY effective against Titans. A person with a strong enough gun could probably blast a titan in the face, and end up killing it by having the bullet reach it's nape and go out the back, lol. In AOT, rifles were able to blind titans if shot in their eyes, by destroying them. Cannons are able to obliterate most titans, other than the armored(since you said no spoilers, I won't use the titans name), and colossal. So it's clear that Titans are susceptible to gunfire. And I think you could take one down with a well placed shot from something like a .44 magnum. I'd be pretty confident with it at least.
With tanks and such though? The titans wouldn't manage to scrape the outsides of their armor, let alone damage the people inside, or withstand machine gun and missile fire from planes and tanks. Now the big three might be able to do some damage, but you center a couple of jets around the colossal, shoot some missiles at the female, and put the armored up against some planes as well, and you're definitely going to bring all three down pretty handily.