Several vaccines can reduce the risk of acquiring and transmitting a disease but do not offer complete protection. Some examples include:
- Influenza vaccine: The flu vaccine's effectiveness varies from year to year because the circulating flu strains can change. Even when the vaccine is well-matched to the circulating strains, some people may still get infected and transmit the virus to others. However, the vaccine can reduce the severity of the illness and the risk of complications.
- COVID-19 vaccines: COVID-19 vaccines, such as Pfizer-BioNTech, Moderna, and AstraZeneca, have shown high efficacy in preventing severe illness, hospitalization, and death. However, breakthrough infections can still occur, and vaccinated individuals may transmit the virus to others, albeit at a reduced rate compared to unvaccinated individuals.
- Pertussis (whooping cough) vaccine: The pertussis vaccine (DTaP for children and Tdap for adolescents and adults) can protect against severe illness, but its effectiveness decreases over time. Vaccinated individuals might still acquire a milder form of the disease and potentially transmit it to others, especially vulnerable populations like infants.
- Varicella (chickenpox) vaccine: The varicella vaccine is effective in preventing severe chickenpox, but some vaccinated individuals might still experience a milder form of the illness (breakthrough varicella) and transmit the virus to others.
These examples underscore the importance of maintaining high vaccination rates within communities to establish herd immunity and protect vulnerable individuals who may not be able to mount a robust immune response to the vaccines or cannot receive them due to specific medical reasons.