The New Paper Vaccines may protect for up to 18 months, third jab may be needed Health Ministry's director of medical services Kenneth Mak said another jab could also be required to guard against new variants of the virus. PHOTO: MCI Individuals vaccinated against Covid-19 may be protected for up to 18 months. Beyond that, additional vaccination shots might be needed if a person's immunity to the virus begins to wane, the Ministry of Health's (MOH) director of medical services Kenneth Mak said yesterday. Another jab could also be required to guard against new variants of the virus, he added, in response to a question at a virtual news conference on plans to administer a third dose of the vaccine.