Spend DNA within the current round that you are playing. You cannot bring it over from round to round. To earn more DNA, at the start of a new game do not purchase any transmissions, resistances, and symptoms. Afterwards, set the game to double speed and wait between 10 to 20 minutes. Pop the yellow DNA bubbles and let the DNA collect on its own until you have about 400. After that, begin buying transmissions then go back in to collect more DNA. When you DNA collection slows down, buy transmissions again. When done, buy the symptoms and start spreading your virus. Infecting new country will let you get DNA. DNA becomes easier to collect once you see people start dying in a new country. Yellow DNA bubbles will randomly pop up from any country you already attacked while red DNA bubbles will pop up from a country that has not been infected before, especially after a red ship or plane arrives. Turn off your device's auto-lock feature to collect DNA without having to check your device.
Easy infection
Wait until you have lots of transmission. Because the cure will speed up once you start purchasing symptoms, wait until you have possible way to transmit your virus into different country around the world before you begin purchasing additional symptoms. The more symptoms you purchase, the faster you can spread the virus however this will also make your disease easier to control by the authorities. Begin spreading your virus in difficult to reach countries, such as Greenland, New Zealand, Madagascar, etc. These are island countries with only few transportation routes. You can then move to infecting as many people as possible by targeting India, Russia, the United States, and Brazil because of their large populations and transportation options.
Gems
Wait for DNA to build up, then buy lots of transmissions and watch how the infections will attack. After you have unleashed a successful attack of infection globally, wait for a green pop up bubble to appear. Tap it to get a gem. You can repeat this trick every round to get free gems. Note: This happens more often under the Hard difficulty setting.
Gene Obfuscation
Wait until the cure is over 50% before purchasing Gene Obfuscation. This modification will lessen the cure percentage of a certain disease. The longer you wait before using it, the more useful its effect will be.
General strategies
The cure will begin to spread even before you can upgrade for more symptoms. You need to purchase infection modifications, starting with purchasing the resistances. Try getting hot and cold resistances as well as water resistances early. You can use the Easy difficulty setting to get past a particularly troublesome level. To unlock next level, you do not need to complete it under a higher difficulty. As you make progress and unlock more pathogens and genes you will eventually be able to complete those difficult levels. You can usually play in double speed without any bad consequences. Tap the fast forward icon to do so. However, always play at normal speed if you have just purchased a large quantity of transmission modifications or you will have trouble keeping up with the red pop-ups. Each pop-up bubble has specific function. For red DNA, you will get one DNA per drop when a new country is infected. The yellow DNA pop-ups appear randomly to any country that has already been infected. There Blue cure pop-ups will slow down the cure percentage. Follow the routes of the red and blue ships and planes to know in advance where an infection or cure will be appearing next.
Genes
Genes are much easier to unlock than pathogens, however there is a limited amount of them. As you complete the game, new genes will be available. Play the game under the easy difficulty setting and complete it to unlock them quickly. You can also unlock additional genes after using the "Get Rare Genes" option by spending gems. Decrease the visibility of your disease by using genes for a more effective attack. This will slow the process for that disease to be cured. Stack two, three or even four visibility decreasing genes together.
Pathogens
When you first start, you will have the opportunity to select what pathogen you want to use (for example, a bacteria or virus). As you use different pathogens to infect the world, the more effective it will become. Your goal should be to continue unlocking pathogens until all of them are available for use in infections. Win a level with the most recently unlocked pathogen under the medium or hard difficulty settings to unlock new pathogens.