Europe's dream of emerging from the shadow of COVID-19 this summer is fading because of new subvariants of the virus.

The BA.4 and BA.5 subvariants of the Omicron strain of the virus have already become the main cause of new infections in many parts of the world, due to their increased infectiousness, ability to partially evade vaccines and resistance to antibody treatments.

According to research by scientists, the subvariants are responsible for more than 50 percent of new COVID-19 cases in the United States and are a major cause of infections in Australia.

David Ho, director of the Aaron Diamond AIDS Research Center at Columbia University, headed the study. "The virus is continuing to evolve, as expected, and it is not surprising that these new, more transmissible subvariants are becoming more dominant around the world," he told Newswire.

Ho said developing new vaccines will be important.

"Understanding how currently available vaccines and antibody treatments stand up to the new subvariants is critical to developing strategies to prevent severe disease, hospitalizations and deaths," he said.

Ho and his team looked at how well antibodies in people who have had at least three doses of a vaccine stand up to the subvariants.

The study, published in the journal Nature, found that the BA.4 and BA.5 subvariants are at least four times more resistant to existing inoculations than previous strains.

The good news was that, while more people will catch the new strains, most fully vaccinated people are still protected from severe illness.

Experts say that the new wave of COVID-19 infections will cause major disruptions this summer, particularly to people's travel plans, as nations consider reintroducing border controls and demanding that travelers be virus-free and fully inoculated.

Layla Moran, a Liberal Democrat member of the United Kingdom's Parliament and the chairwoman of its All-Party Parliamentary Group on Coronavirus, told The Mirror newspaper, "It is possible that holiday plans will be ruined due to rising COVID rates."

She said nations might now "reintroduce restrictions" that will not only disrupt holidays but put a dent in the international shipping of goods and services.

Additionally, Europe is likely to see an "increase in staff shortages, with more people off sick with the virus", she said.

The recent spike in infections led the UK's Office for National Statistics to record 1.8 million new infections during the week ending June 24, the most in two months.

Spain registered a 62 percent jump in COVID-19 cases in the week ending July 1, compared with two weeks earlier.

In the two-week period ending July 4, France saw a 78 percent jump in infections, taking the nation's total to the highest level since April.

Even Germany, which has done better than most European nations in limiting the spread of the virus, said its COVID-19 cases had reached a two-month high, almost doubling in a two-week period.

Italy, which was hit particularly hard by the initial wave of the pandemic, saw its infections hit a five-month high in the week ending July 4.

And Greece, one of Europe's most virus-ravaged nations and one of its most popular holiday destinations, recently had 1,441 new daily cases of COVID-19 for every 1 million residents-around double the rate of just two weeks before.

Martin McKee, president of the British Medical Association, told Mail Online the rising case numbers clearly show that Europe is "not out of the woods yet".

Reuters noted that the new subvariants were added to the World Health Organization's list of mutations in need of monitoring in March. Since then, they have surged to the fore, with the US Food and Drug Administration now recommending that COVID vaccine makers focus on trying to combat them.

The quick spread, particularly in nations with loose border controls, has put the spotlight back on countries such as China that have maintained relatively strict policies around travel.

Hans Kluge, the WHO's regional director for Europe, said that "countries across the European region have lifted the social measures that were previously in place", and that means "the virus will transmit at high levels over the summer".