The COVID-19 vaccine provides protection against the disease as a result of the development of immunity system against the SARS-Cov-2 virus. In this case, the development of immunity system by vaccination means that the risk of the disease and its consequences are reduced. Vaccines do not completely cure the disease and the immune system helps fight the virus if it is exposed.
Getting vaccinated can protect the people around you, because if you protect yourself from infection and disease, you are less likely to infect someone else. There is particular importance is the protection of people with chronic illnesses, health care providers, the elderly, and people with other health conditions from those at high risk for serious illnesses from COVID-19.
An important feature of viruses is their constant occurrence of variant. Further studies are needed to assess the effectiveness of current COVID-19 vaccines against new strains. Current vaccine data and its effectiveness suggest that many vaccines stimulate the immune system to maintain significant efficacy against many strains, especially for serious illness, hospitalization, and death.
Vaccines have a broader immune response to significantly protect against disease, which means that the vaccine cannot be completely ineffective due to viral mutations or mutations. If one of these vaccines is less effective against one or more of these strains, it is likely that the composition of the vaccine will change to protect against each of those strains, however, this will require time, cost and a wide range of vaccination data to fully evaluate. Data collection and analysis of new strains of the COVID-19 virus are ongoing.
The World Health Organization (WHO) will update its guidelines when it learns more about the effects of specific strains on specific vaccines. The World Health Organization is regularly reviewing this evidence. As we learn more, we must do everything possible to stop the spread of the virus to prevent the spread of mutations that can reduce the effectiveness of existing vaccines.
Source : Coronavirus disease (COVID-19): Vaccines
https://www.who.int