The third dose mostly refers to the third dose of the Neocollins vaccine. It is still possible to be infected after the third dose, but the probability is relatively low or the likelihood of becoming seriously ill is reduced. Even if you have completed the third dose of the Neocollins vaccine, it does not mean that you will not be infected by Neocollins 100% of the time, and there is still a possibility that you will be infected by Neocollins. Because of the mutation of the new coronavirus, the old vaccine is unable to prevent it completely. Meanwhile, due to the different immunity and physical fitness of different groups of people, the number and titer of antibodies that can be formed after vaccination are also different, thus affecting the effectiveness of protection to a certain extent. However, after receiving the third vaccination, the probability of infection by the new coronavirus can be significantly reduced, and even if infection occurs, the probability of becoming seriously ill is significantly lower than that of people who have not received the third vaccination.