Vaccine- are a little bit of the virus that is dead so your body can make antibodies that can fight off the virus.

Zinc Sulphate- a medicine

Formally improved -Approved from the Government 

Medical Benefit- Helping your body fight.

Undoubtedly- probably, definitely 

Spray inhalers - a gas you breathe in through your nose/mouth, think of an asthma inhaler.

benefit/beneficial - mean the same thing

Michael-in 1918 there were no flu vaccines and no medicine that could treat complications from the flu. Breathing in zinc sulphate gas, which was thought to prevent the spread of the disease. The medical benefits didn't make everyone better, it made everyone sick because they were all in the same room helping others but when they are helping others they become sick because they were breathing on each other. After the war everybody was having parties, getting drunk. When they had parties they gave each other the flu/virus.