The WHO forecasts that people most vulnerable to Covid-19, such as the elderly, will need to get an annual vaccine booster to be protected against variants. Vaccine makers Moderna Inc and Pfizer Inc have been vocal in their view that the world will soon need booster shots to maintain high levels of immunity.The WHO forecasts that people most vulnerable to Covid-19, such as the elderly, will need to get an annual vaccine booster to be protected against variants. Vaccine makers Moderna Inc and Pfizer Inc have been vocal in their view that the world will soon need booster shots to maintain high levels of immunity.