Infectious diseases are caused by microorganisms such as bacteria, viruses, fungi, and parasites. These microorganisms can spread from one person to another through various modes of transmission. While the options (a), (b), and (c) are all modes of transmission that can lead to the spread of infectious diseases, option (d) - vaccination of diseases - is not a cause for the spread of infectious diseases. Let's discuss each option in detail:

a) By vectors and carriers:
Vectors are organisms (typically insects) that can transmit infectious diseases from one host to another. For example, mosquitoes can transmit diseases like malaria, dengue fever, and Zika virus. Carriers, on the other hand, are individuals who are infected with a pathogen but do not show any symptoms. They can unknowingly transmit the disease to others. For example, carriers of hepatitis B virus can spread the disease through blood or bodily fluids.

b) By air directly or as droplets:
Airborne transmission occurs when infectious agents are present in the air and can be inhaled by others. This can happen when an infected person coughs, sneezes, or talks, releasing respiratory droplets containing the pathogens. Diseases like tuberculosis and influenza can spread through airborne transmission.

c) By intimate contact:
Intimate contact refers to close physical contact with an infected person or their bodily fluids. This can include activities such as kissing, sexual contact, or sharing personal items like toothbrushes or needles. Sexually transmitted infections like HIV/AIDS and herpes can be transmitted through intimate contact.

d) By vaccination of diseases:
Vaccination is a preventive measure against infectious diseases. It involves administering a vaccine that contains weakened or killed pathogens or their parts to stimulate the immune system to produce an immune response. This helps the body recognize and fight against specific pathogens, providing immunity to the disease. Vaccination does not cause the spread of infectious diseases; instead, it helps prevent their spread by providing immunity to individuals.

In conclusion, option (d) - vaccination of diseases - is not a cause for the spread of infectious diseases. Instead, it is a preventive measure that helps control the spread of infectious diseases by providing immunity to individuals.