Health experts are urging people to get their flu booster jabs to contain the virus during the colder months. The UK Health Security Agency (UKHSA), the government agency responsible for public health, is urging eligible people to get the flu booster jab. They are particularly urging pregnant women and those with underlying health conditions to come forward, but also people from a black Caribbean or black African background, after data suggested that they have had the lowest uptake of the vaccine. While many people aged 65 and over have already come forward for their flu vaccination, exceeding the WHO target of 75%, less than half of those with underlying health conditions have had the flu jab. The UKHSA is aiming to increase that number. The amount of pregnant women opting for the jab is also lower, with only 34.4% vaccinated this season. What date do I need to get the flu jab by to be protected at Christmas? The agency said the vaccine takes 14 days before it provides maximum protection. For those wanting full protection from the virus on Christmas Day - 10 December is the best day to get vaccinated. What the Government said about flu jabs Health and Social Care Secretary, Sajid Javid said: "Getting your winter vaccines – whether that is your flu jab if eligible or your booster jab - is one of the most important things people can do for yourself and your family this winter. "Don’t delay – book your flu vaccine as soon as possible." The UKSHA have stressed the flu is highly infectious and can lead to serious complications for those with a long-term health condition. ‘The threat of flu has not gone away’ Dr Conall Watson, Consultant Epidemiologist at UKHSA, said: "The threat of flu has not gone away – it can cause serious illness and be fatal. Flu vaccination saves lives. If you are eligible, you don’t have to wait to be called up - book your flu vaccine as soon as possible to help protect yourself and your family this Christmas." Who is eligible for a free flu vaccine? In England, more than 35 million people are eligible for a free flu vaccine this winter. This includes people aged 65 and older, pregnant women and those with underlying health conditions. Children aged 2-3 years on the 31 August and school children aged up to 16 are also eligible for a free flu vaccine. Eligible adults can book their flu vaccine through their GP or local pharmacy. Mums-to-be can also get their jab at their maternity service whilst children are being offered a quick and painless nasal flu spray. Frontline health and social care workers should be offered through their employer or for some staff groups, through their GP or pharmacy, the UKSHA says. A version of this article originally appeared on NationalWorld.com