While infection risks for vaccinated people have shown to decrease substantially after vaccination, certain variants have already been found to have mutated enough to decrease the vaccine's efficency
The latest study, which has not yet been peer reviewed, was conducted on 10 mutations, which are characteristic of the variant known as B117 identified in Britain.
The new method successfully detected the British variant in sewage samples in Beersheba.
The world faces around 4,000 variants of the virus that causes COVID-19, prompting a race to improve vaccines, Britain said on Thursday.
Despite the higher risk, evidence showed that both vaccines being used in the country were effective against it.
The British mutation has likely spread much more rapidly across the country. It could impact the lockdown timetable.
The four cases are from two separate chains of infection - one from an individual who returned from South Africa and another who was infected by one of the person's family members.