Meningococcal vaccine refers to any vaccine used to prevent infection by Neisseria meningitidis. Different versions are effective against some or all of the following types of meningococcus: A, B, C, W-135, and Y. The vaccines are between 85 and 100% effective for at least two years. They result in a decrease in meningitis and sepsis among populations where they are widely used. They are given either by injection into a muscle or just under the skin.The World Health Organization recommends that countries with a moderate or high rate of disease or with frequent outbreaks should routinely vaccinate. In countries with a low risk of disease, they recommend that high risk groups should be immunized. In the African meningitis belt efforts to immunize all people between the ages of one and thirty with the meningococcal A conjugate vaccine are ongoing. In Canada and the United States the vaccines effective against four types of meningococcus (A, C, W, and Y) are recommended routinely for teenagers and others who are at high risk. Saudi Arabia requires vaccination with the quadrivalent vaccine for international travellers to Mecca for Hajj.Meningococcal vaccines are generally safe. Some people develop pain and redness at the injection site. Use in pregnancy appears to be safe. Severe allergic reactions occur in less than one in a million doses.The first meningococcal vaccine became available in the 1970s.
Proliferative vitreoretinopathy (PVR) is a disease that develops as a complication of rhegmatogenous retinal detachment. PVR occurs in about 8–10% of patients undergoing primary retinal detachment surgery and prevents the successful surgical repair of rhegmatogenous retinal detachment. PVR can be treated with surgery to reattach the detached retina but the visual outcome of the surgery is very poor. A number of studies have explored various possible adjunctive agents for the prevention and treatment of PVR, such as methotrexate, although none have yet been licensed for clinical use.PVR was originally referred to as massive vitreous retraction and then as massive periretinal proliferation. The name Proliferative vitreo retinopathy was provided in 1989 by the Silicone Oil Study group. The name is derived from proliferation (by the retinal pigment epithelial and glial cells) and vitreo retinopathy to include the tissues which are affected, namely the vitreous humor (or simply vitreous) and the retina. Predisposing factors
Predisposing factors for Postoperative PVR are preoperative PVR, aphakia, high levels of vitreous proteins, duration of retinal detachment before corrective surgery, the size of the retinal hole or tear, intra-ocular inflammation, vitreous hemorrhage, and trauma to the eye. An equation to calculate the patients risk for acquiring PVR is:

PVR score = 2.88 × (Grade C PVR)+ 1.85 × (Grade B PVR) + 2.92 × (aphakia) + 1.77 × (anterior uveitis) + 1.23 × (quadrants of detachment) + 0.83 × (vitreous haemorrhage) + 23 × (previous cryotherapy)1 is added if the risk factor is present and 0 if the risk factor is absent.