Conspiracy theory, with no evidence provided to support the claim. This is part of a disinformation campaign on coronavirus, well documented by both media and governments. Elements of this campaign were widely reported by Russian and international publications, and by the European External Action Service.
NATO pays special attention to the vaccination, NATO forces should have adequate immunity against several known diseases, like Diphtheria, Measles, Pertussis, Polio, Rubella, and Tetanus. And if necessary, should be vaccinated prior to exposure to these diseases: Hepatitis A and B, Japanese Encephalitis, Meningitis, etc. However, NATO soldiers could not have been vaccinated against COVID-19, as there is no vaccine against novel coronavirus. It can take a number of years for a new vaccine to be developed.
This disinformation message appeared in the same article as the claims that COVID-19 is a biological weapon created by Bill Gates, George Soros and the "Deep state", that The most powerful virus has been brought to Italy by Gladio, NATO's secret terrorist network, and that The "operation COVID-19" should have led to the overthrow of three world leaders.